ICES Symposium on

Brackish Water Ecosystems

Helsinki, 25-28 August 1998

ABSTRACTS OF ORAL PRESENTATIONS

1. Biochemical monitoring of brackish water ecosystems
Alina Agatova, Nataliya Lapina, Nadezhda Torgunova and Konstantin Kirpichev

2. Ecological aspects of the biochemical studies in the Black Sea coastal waters
Alina Agatova and Victor Sapozhnikov

3. Currents in the entrance of the Gulf of Finland in 1994
Pekka Alenius

4. The ecosystem modelling of the Baltic Sea and estimation of cod larvae transport from the main spawning ground in the southern Baltic
E. Aro, R. Tamsalu, K. Myrberg and K. Keto

5. Fish production and fishery in the northern Baltic
Paula Böhling and Petri Suuronen

6. Long-term changes in the soft bottom macrofauna of the Gulf of Riga
Hans Cederwall and Vadims Jermakovs

7. Current state of zoobenthos in two estuarine Bays of the Barents and Kara Seas
N. Denisenko, H. Sandler and S. Denisenko

8. New aspects of investigations of the relict Mogilnoe Lake ecosystem
Svetlana S. Drobysheva, Leonid I. Serebrov, Mikhail Yu. Antsiferov and Natalia F. Plotiszyna

9. The structure of the nanophytoplankton community in the Marsdiep basin of the Wadden Sea (North Sea) during the winter and spring periods
E.I. Druzhkova and N.V. Druzhkov

10. The submarine seepage of fresh water: disturbance in hydrological and chemical structure of the water column in the Gdansk deep
Lucyna Falkowska and Halina Piekarek-Jankowska

11. Towards optimal sea ice monitoring in the Baltic Sea
Hannu Grönvall and Ari Seinä

12. Seasonal and long-term control of the bottom water oxygen deficiency in a stratified shallow water coastal system
Hans Peter Hansen, Hanna C. Giesenhagen and Gerda Behrends

13. Long-distance nutrient transport and eutrophication in the Archipelago Sea, northern Baltic: a 3-D hydrodynamic model study
H. Helminen and P. Laihonen

14. Five-year monitoring experience at the high-frequency station in the Gulf of Riga, Baltic Sea
Anda Ikauniece, Mikelis Mazmachs and Baiba Kalveka

15. Phytoplankton assemblages in relation to an arctic fjord environment in summer
Alexander Keck, Józef Wiktor, Ryszard Hapter and Rune Nilsen

16. Gas bubble concentrations measured acoustically in the Baltic Sea
Zygmunt Klusek and Jaromir Jakacki

17. Small scale distribution of zooplankton around drifting buoy in central Baltic
Alexandr Korshenko

18. Is Prymnesium parvum toxic for copepods? - Grazing, egg production and egestion of a calanoid copepod Eurytemora affinis in mixtures of ‘good’ and ‘bad’ feed
Marja Koski, Mirja Rosenberg, Markku Viitasalo, Sanna Tanskanen and Ulla Sjölund

19. Phytoplankton - the main factor responsible for transport of PAHs from water to sediments in the southern Baltic ecosystem
Grazyna Kowalewska

20. Vertical distribution of heavy metals in sediments of the Gulf of Riga and of the mouths of Daugava and Lielupe
Irina Kulikova and Zinta Seisuma

21. Influence of hydrography on microbial dynamics in the river Guadiana in southern coast of Portugal
Jorma Kuparinen, Helena Galvão, Ana Barbosa, Pedro Mendes and Margarida Reis

22. Role of the temperature factor for the intensiveness of production-destruction processes in brackish water ecosystems of south and arctic seas
Nataliya Lapina and Alina Agatova

23. Seasonal fluctuations in growth, metabolism and chemical composition of some important macrozoobenthos species in the Gulf of Riga
Kari Lehtonen, Hans Cederwall and Vadims Jermakovs

24. Distribution and massbalances of metals in surface sediments of the Gulf of Riga (the Baltic Sea)
Mirja Leivuori, Irina Kulikova, Zinta Seisuma, Valter Petersell, Kestutis Jokšas, Birger Larsen, Britta Pedersen and Heldur Keis

25. Operational environment monitoring and information system for the Gulf of Finland, the Baltic Sea
Juha-Markku Leppänen, Eija Rantajärvi, Seija Hällfors, Mikaela Ahlman and Urmas Lips

26. The structure of benthic littoral communitites of West Estonian Archipelago Area as a reflection of unique ydrodynamical conditions
Georg Martin and Henn Kukk

27. Winter flounder (Pleuronectes americanus) from the anthropogenically-impacted western Long Island Sound, NY (USA): respiratory responses and adaptations to hypoxia
Maryann McEnroe and Don Krozlowitz

28. Dynamic of river plumes in the Pomeranian Bight
V. Mohrholz, H.U. Lass and A. Mutzke

29. Chlorophyll in the White Sea
Nataliya Mordasova

30. Modelling the physical processes of the Gulf of Finland by using two-and three-dimensional hydrodynamic models
Kai Myrberg

31. Food consumption by clupeids in the central Baltic: Is there evidence for Top-down control?
C. Möllmann and W.F. Köster

32. Production-destruction processes in the White Sea
Irena Naletova and Victor Sapozhnikov

33. Recent changes in the Gulf of Riga ecosystem as compared to the previous two decades
H. Ojaveer, A. Lankov, A. Lumberg, A. Turovski, I. Kotta, J. Kotta and M. Eero

34. The Puck Bay (southern Baltic) - fisheries management in a very specific brackish water system
Wojciech Pelczarski

35. Fate of organic matter and nutrients along the estuarine gradient in the eastern Gulf of Finland, Baltic Sea
Heikki Pitkänen, Anna-Stiina Heiskanen, Vesa Gran and Jouni Lehtoranta

36. Several peculiarities of the vertical hydrochemical structure of the Baltic Sea
Victor Sapozhnikov and Irena Naletova

37. Sedimentation processes in the jet flow of river-lake contact zones
B. Shteinman, Y. Kamenir, T. Bergstein Ben-Dan, A. Hochman and O. Itzhak

38. Northern Caspian Sea water pollution with Volga run-off in 1993-1995
Andrei Skorokhod and Lidia Lisitzyna

39. Nutrient limitation in the Archipelago Sea: experimental and nutrient-ratio approaches
Janne Suomela, Harri Helminen, Kauko Häkkilä, Teija Kirkkala, Helmi Kotilainen and Pasi Laihonen

40. Denitrification, pore water profiles and nitrogen fluxes in the sediment of the northern Baltic Sea
Liisa Tuominen, Kalervo Mäkelä, Hannu Haahti, Kari Lehtonen, Susanna Hietanen and Jorma Kuparinen

41. Relation between dispersal and nursery areas
Lauri Urho

42. Concentrations of heavy metals in fishes from coastal waters around the Baltic Sea
Heinz-Rudolf Voigt

43. Relations between runoffs, salinity and zooplankton in the Baltic Sea, from monitoring towards prediction
Ilppo Vuorinen and Jari Hänninen

44. Salinity, suspensions and sedimentation gradients influence on Arctic tidal flat benthos
Jan Marcin Wêslawski, Maria Szymelfenig, Marek Zajczkowski and Alexander Keck

45. Primary production and decomposition of organic matter in the epipelagic zone of the Gulf of Gdañsk, an estuary of the Vistula River
Zbigniew Witek, Stanislaw Ochocki, Jan Nakonieczny, Beata Podgorska, Aleksander Drgas and Alfred Grelowski

 

1. Biochemical monitoring of brackish water ecosystems
Alina Agatova, Nataliya Lapina, Nadezhda Torgunova and Konstantin Kirpichev

Organic matter (OM) is an integral and liable parameter, which reflects all changes in the marine ecosystem. Methods for determination of the concentrations of total dissolved and particulate organic carbon (DOC and POC) and main biochemical components, i.e. proteins, carbohydrates, lipids, and nucleic acids on board have been developed and tested. A comparative analysis of the efficiency of the UV and persulfate oxidation and high temperature catalytic oxidation on TOC-500 (HTCO) for determination of dissolved organic carbon (DOC) has bee performed. The universality of the HTCO against DOC is shown on the examples of two seas.

Rates of OM transformation are determined by assessment of activity of different enzymes (protease, phosphatase, cellulase, and enzymes of oxidation and reduction). These methods have been used in biochemical monitoring of shelf and deep waters ecosystems in the Black and White Seas. Main differences and similarities in OM content, biochemical composition and rates of transformation have been found for ecosystems of shelf and deep waters both in the same and between the two seas. For the ecosystems of brackish waters of the Black and White Seas, seasonal and interannual variability of the parameters has been found. It is especially vivid in the bays of the White Sea. The river input of DOC and POC is assimilated by the marine ecosystem rather fast. The area of river and seawaters interaction is characterized by the increased activity of hydrolyzes and enzymes of oxidation and reduction processes in microplankton and microbenthos.

Alina Agatova, Nataliya Lapina, Nadezhda Torgunova and Konstantin Kirpichev: Russian Federal Research Institute of Fisheries and Oceanography, 17-a V. Krasnoselskaya, 107140 Moscow, Russia.

2. Ecological aspects of the biochemical studies in the Black Sea coastal waters
Alina Agatova and Victor Sapozhnikov

The biohydrochemical regime in the coastal Black Sea was studied at the Caucasus, Crimea, and Bulgarian coasts. A macroscale decrease in the concentrations of dissolved organic matter (OM) was observed from the north-western shallow waters and the Danube river-mouth, along the Romania, Bulgaria, and then Turkey and the Caucasus up to the South Crimea. The maximal values of primary production, chlorophyll and contaminations were also observed at the north-western shallow waters, with the concentrations gradually declining towards the Caucasus coasts. Eutrophia in the coastal waters drives a phytoplankton bloom which could be equal to a "red tide". The intensity and products of metabolism of this microflora determine whether the ecosystem overcome the antropogenic pressing.

Thus, in the summer of 1989, the phytoplankton biomass made 103.7 g/m³ in the coastal zone of Varna Bay. Then the dominating species was Goniaulax polyedra. The biohydrochemical analysis of the reasons of the harmful algae bloom showed an intensive accumulation of the products of glykolytic splitting of sugars (the high activity of the lactat-dehydrogenase enzyme) and the hydrolytic splitting of phosphorus organic compounds (the high activity of alkaline phosphatase) on the Bulgarian shelf (Varna Bay). Mean while, the activity of the enzymes of electron transport system (ETS) which oxidize the destruction products to CO2 equaled analytical zero.

As a result of the accumulation of the products of half-destruction of OM a strong eutrophication of the waters occurs with the perediniums shift to the heterotrophic feeding, which is the reason of the "red tide". During the "red tide" the ETS enzymes grow active, a rapid regeneration of nutrients as a result of the OM intensive oxidation and a rapid growth in the autotrophic biomass of phytoplankton.

The mechanisms of back-ties between Goliaulax polyedra development at the low-molecular OM, and on nutrients are discussed.

Alina Agatova and Victor Sapozhnikov: Russian Federal Research Institute of Fisheries and Oceanography, 17-a V. Krasnoselskaya, 107140 Moscow, Russia.

3. Currents in the entrance of the Gulf of Finland in 1994
Pekka Alenius

Current measurements were done at five stations along a section from Hanko peninsula to Osmussaar in the entrance of the Gulf of Finland in the Baltic Sea. The stations were evenly distributed across the mouth of the Gulf of Finland. Two current meters, one at 8 m depth and the other at 45 m depth were used at each mooring. Measurements were done with 10 min intervals from 10th of May to 18th of October. Mean current speed was rather low at each station, between 8 and 11 cm/s. The average speed was larger near the coasts and slower in the middle of the gulf. Near the coast of Finland the current was more often directed towards west than towards east. Near the coast of Estonia the distribution of current directions to into the gulf and out from the gulf direction was more even. In the middle of the gulf the current direction was more variable than near the coasts.

Pekka Alenius: Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland.

4. The ecosystem modelling of the Baltic Sea and estimation of cod larvae transport from the main spawning ground in the southern Baltic
E. Aro, R. Tamsalu, K. Myrberg and K. Keto

The latest version of coupled three dimensional hydrodynamic and ecosystem model FinEst has been used to simulate seasonal ecological events in the Baltic Sea and as well as cod larvae transport outside the main spawning ground in the Bornholm Basin. Seasonal succession of the biomass of five autotroph and five heterotroph size glasses has been calculated for the whole Baltic Sea Main Basin. The ecosystem simulations showed the seasonal pattern of spring and late summer blooms of plankton biomass by size groups. The late summer plankton bloom in the nutrient poor upper layer was limited by the nutrient transport from the nutrient rich lower layer. The interaction between these layers showed a significant coupling in the intensity of the bloom. The cod larvae transport was simulated both by using an eulerian approach, where number of drifters were released at the Bornholm Basin and their trajectories were calculated and by lagrangian co-ordinate system releasing the larvae patches in the Bornholm Basin at depths of 35 m and 45 m. The simulations for larvae drift were done for August 1991 and July-August in 1994. These experiment showed a high non-linear nature of the current system. After one month simulation period there were significant differences in the final position between drifters launched at a small area. There were pronounced differences between the trajectories in simulations, where the initial dept of the drifters was 35 m and 45 m. These results indicate a need of a high vertical resolution for a hydrodynamic models.

E. Aro: Finnish Game and Fisheries Research Institute, P.O. Box 6, FIN-00721 Helsinki, Finland.

R. Tamsalu: Estonian Marine Institute, Paldiski Str. 1, EE0001 Tallinn, Estonia.

K. Myrberg and K. Keto: Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland.

5. Fish production and fishery in the northern Baltic
Paula Böhling and Petri Suuronen

The northern Baltic Sea with its wide coastal areas, archipelagoes and rivers descending into it support a high fish production. Due to the salinity gradient the fish community is composed of both freshwater and marine species. The relative abundances of the fish species, the production and the status of the stocks are influenced by environmental factors, fishing and stocking.

The biomass of the stocks of Baltic herring is large. Herring is the most important target species for the professional fishery and especially the stocks in the Bothnian Sea are efficiently utilized. If the fishing pressure remains at the 1997 level, the biomass will decline in the northern Baltic. The stocks of Baltic cod have decreased due to overfishing and unfavorable environmental conditions in the spawning areas. As there is little cod in the sea, the stocks of sprat are exceptionally large.

Many of the spawning rivers of Baltic salmon, anadromous whitefish and sea-trout have been dammed and the reproduction areas partially destroyed. The natural production is low and the fishery highly based on stocking. The offshore fishery and most of the coastal fisheries exploit both wild and reared populations. The wild stocks are overfished.

Pike-perch has benefited from the eutrophication of coastal waters and the stocks have greatly strengthened during the past three decades. There is too much fishing pressure on young fish which reduces the productivity of the stocks. The stocks of pike, perch and vendace are also abundant and effectively utilized.

Assurance of the natural fish production requires sustainable fishery. Fishing efficiency has to remain at a level which ensures the maintenance of an adequate spawning stock for the renewal of the stock. When natural reproduction has been weakened or completely prevented and feeding areas are still available, fishing can be maintained by stocking.

Paula Böhling and Petri Suuronen: Finnish Game and Fisheries Research Institute, P.O. Box 6, FIN-00721 Helsinki, Finland.

6. Long-term changes in the soft bottom macrofauna of the Gulf of Riga
Hans Cederwall and Vadims Jermakovs

Studies of Gulf of Riga macrozoobenthos 1993-1996, compared with earlier studies, shows that significant changes has taken place.

Total abundance was about the same as during the 80s, but only 70 % of the 70s. Total biomass of the 90s was slightly higher than during the 70s, but only about half of the 80s.

Abundance and biomass of Monoporeia affinis have decreased with 50-70 % during the last decade. This decrease was extreme in deeper areas, while in shallower areas the species increased. Pontoporeia femorata, important in the deep areas during the 70s, decreased during the 80s, and still showed very low figures.

Macoma balthica, showed higher abundance and biomass figures during the 80s than during the 70s. Since then abundance has increased slightly, while the biomass has nearly doubled.

During the 70s and 80s annelids made up less than 25 % of the abundance and 1 % of the biomass. The arrival of Marenzelleria viridis, in 1988, changed that dramatically. It is now the most abundant species, found all over the gulf. It also has the next highest mean biomass. The annelid part of the abundance and biomass has increased to 42 and 12 %, respectively.

The decrease of M. affinis and increase of M. viridis, has reduced crustacean abundance from 56 to 34 and biomass from 14 to 9 %.

Annual production of macrozoobenthos in the gulf was estimated to 15 tons for 1985-89, but only 7 tons for 1993-96. Community annual turnover rates were estimated to ca 0.5 for both the 80s and the 90s.

Hans Cederwall: Department of Systems Ecology, University of Stockholm, S-106 91 Stockholm, Sweden.

Vadims Jermakovs: Institute of Aquatic Ecology, Latvian University, Miera str. 3, LV-2169 Salaspils, Latvia.

7. Current state of zoobenthos in two estuarine Bays of the Barents and Kara Seas
N. Denisenko, H. Sandler and S. Denisenko

At the beginning of 1990s, Finnish Institute of Marine Research in cooperation with Murmansk Marine Biological Institute, within the framework of the Finnish-Russian Offshore Technology Working Group, initiated the research program to study the natural environment and biota of the Barents and Kara Seas. The aim of the studies was to build up a reliable database on the spatial distribution and taxonomic structure of the benthic communities in study areas. These data can be used as the baseline information for monitoring the water environment and biota changes due to multiannual climatic fluctuations, oil and gas production impacts and increasing navigational activities, etc.

A part of the studies was carried out in two large bays, completely different in morphology, but influenced by strong fresh water outflow. One of them is the Pechora Bay, located in the Pechora Sea (south-eastern part of the Barents Sea), and another one is the Ob Bay in the Kara Sea. In the first case the material was collected in 1995, and the station net covered the whole area with depth more than 6 m. In the Ob Bay, the samples were collected in 1993 and 1996, and the stations were situated mostly to the North from the Taz Bay both in fresh water and estuarine zones.

The numbers of stations in the Pechora and the Ob Bays were 24 and 22 correspondingly. The material was collected with 0.1 m² van Veen grab in 3-5 replications and processed according recommendations of Paris Commission (1988), including, in addition, species biomass (alcohol weight) determination. The dominating role of different species in zoobenthos communities at the stations was determined by calculation the values of relative species production. These values were used to estimate the similarity between samples according to Czekanovsky index. The clusters were determined with original QU-Basic program.

More than 150 different taxa were recorded in the samples from both Bays. The number of taxa in each sample varies from 10 to 52 in the Pechora Bay and from 5 to 43 in the Ob Bay. The Shannon diversity changed within the interval 0.47-2.73 in the Pechora Bay and 0.5-3.2 in the Ob Bay. Biogeographical composition of the bottom fauna in the Ob Bay had more Arctic character and changed along the meridian direction more strictly than in the Pechora Bay.

The total abundance ranged from 350 to 10000 ind./m² in the Pechora Bay and from 100 to 3000 ind./m² in the Ob Bay. The variations of biomass were of the similar order in both Bays, but in the Pechora Bay its values ranged between 2.57 and 212.2 g/m², while in the Ob Bay it ranged between 0.4 and 120.0 g/m². The highest values of the total abundance and biomass in the Pechora Bay were registered in its southern and central part correspondingly, in the Ob Bay - in the northern part.

Clusterization allowed to determine in both bays several communities, which have mostly brackish and freshwater characters. Locations of the communities demonstrate strong dependence on environmental conditions in both study areas, especially of freshwater out flow and grain-size composition of bottom sediments.

Our investigations essentially complement the information that has been available concerning taxonomic composition, abundance, biomass and formation of zoobenthos communities both the in Ob and the Pechora Bays. The results can be used, not only for monitoring studies, but also for estimation the productivity of benthos feeding fish in Arctic estuarine zones.

N. Denisenko and S. Denisenko: Murmansk Marine Biological Institute, 183010, 17 Vladimiskaya str. Russia.

H. Sandler: Finnish Institute of Marine Research, P.O. Box 33, 00931 Helsinki, Finland.

8. New aspects of investigations of the relict Mogilnoe Lake ecosystem
Svetlana S. Drobysheva, Leonid I. Serebrov, Mikhail Yu. Antsiferov and Natalia F. Plotiszyna

The Unique, with no analogues in the world, the relict Mogilnoe Lake is situated on the Kildin Island in the Barents Sea. From the sea strait it is separated by some kind of isthmus which is the medium for filtration and replenishment of the lake with sea water. The upper layer of the lake down to 4 m is brackish and has salinity of 3.7 p.s.u. The lower waters salinity is 30 p.s.u. At depth from 10 m down waters are saturated with hydrogen sulphide. Freshwater and marine organisms inhibit the lake, including Gadus morhua kildensis Derjugin, cod subspecies.

Investigations of 1997 were conducted following more than 20 years break. They showed stable structure of the lake waters. Biomass of marine and freshwater zooplankton per 1 m³ of the Mogilnoe Lake was 10 and 125 times higher than that in the adjacent sea and freshwater lake, respectively. Cod biomass per unit area of the Mogilnoe Lake was a triple amount of that in the Barents Sea and 10 times as high as total mean fish biomass of tundra freshwater lakes. All the above along with high content of biogenic compounds indicate the increased bioproductivity of the Mogilnoe Lake.

Svetlana S. Drobysheva, Leonid I. Serebrov, Mikhail Yu. Antsiferov and Natalia F. Plotiszyna: Polar Research Institute of Marine Fisheries and Oceanography (PINRO), 6 Knipovich Street, Murmansk, 183763, Russia.

9. The structure of the nanophytoplankton community in the Marsdiep basin of the Wadden Sea (North Sea) during the winter and spring periods
E.I. Druzhkova and N.V. Druzhkov

The nanophytoplankton (2-20 pm) were studied on the station of long-term coastal monitoring (Netherlands Institute for Sea Research, Texel, Den Burg) in the Marsdiep basin of the Wadden Sea (the southern North Sea) from October 1993 to May 1994. The study was carried out using the methods of the epifluorescence microscopy. By the end of the growth period (late October), the biomass of the nanoplanktonic algae fell rapidly from 200 down to 50 mg dm (wet weight). During the winter (November-March) it was rather low (20-80 mg dm). The steady increase of biomass stated in the early April and lasted till the end of sampling in the late May. By this time the number of autotrophic flagellates reached up 3.5 x 10 cells dm³, and the biomass 300 mg dm. One of the most prominent peculiarity of the nanophytoplankton biomass dynamics was the succession of equilibrium stages (45-50 days long) at which the biomass rested relatively stable. These stages were separated by the periods of rapid jump-like changes in the biomass lasting for a few days. Recently, the cyclicity of such a type has been described for the coastal ecosystem of the Barents Sea (Druzhkova et al., 1992). Unfortunately, till now the nature of this phenomenon is essentially unclear, although it seems correlated to the synoptic cycles of major nutrients.

Elena I. Druzhkova and Nikolay V. Druzhkov: Murmansk Marine Biological Institute, 17 Vladimirskaya str., 183010 Murmansk, Russia.

10. The submarine seepage of fresh water: disturbance in hydrological and chemical structure of the water column in the Gdansk deep
Lucyna Falkowska and Halina Piekarek-Jankowska

Certain anomalies were observed in the thermohaline and chemical stratification of water column in the Gdansk Basin. The disturbances showed off in the decline of salinity and an increase of sea water temperature in the near bottom layer. The authors are of the opinion that the disturbances were caused by fresh groundwater, drainage from Cretaceous water bearing horizons. Turbulent convection zones were found straight over the seepage area, with Rayleigh thermohaline number in the range 10e15-10e16. Due to very strong thermohaline convection, the pycnocline was forced and an intrusion of more saline water ascended into the surface, less saline, water layers. Simultaneous to the observed convection effects, redistribution of nutrients, accumulated below the pycnocline, was observed in the water column and an improvement of oxygen conditions in the near bottom water.

Lucyna Falkowska and Halina Piekarek-Jankowska: University of Gdansk, Institute of Oceanography, Ave. J. Pilsudskiego 46, 81-378 Gdynia, Poland.

11. Towards optimal sea ice monitoring in the Baltic Sea
Hannu Grönvall and Ari Seinä

In 1996-98 CEC funded project "Operational Sea Ice Monitoring by Satellites In Europe" (OSIMS) the consortium of NERSC, FIMR and DMI have studied the solutions for optimal use of EO data in sea ice monitoring by analysing possibilities and user requests of technical feasibility of missions, instruments and ground structure including better communication means. FIMR made contributions for the Baltic Sea.

The two most heavily marine operated areas in the word, where the seasonal sea ice plays an important role in the navigation, are the Gulf of St. Lawrence in Canada and the Baltic Sea in Europe. The Baltic Sea has a seasonal ice cover lasting up to half a year. The maximum annual ice cover in the Baltic Sea ranges 12-100 % of 420,000 sq. km. This means that sea ice makes navigation difficult at least in Finland, Sweden, Russia and Estonia. Winter navigation is made possible by the use of icebreakers, ice-strengthen vessels and by restricting the navigation. All this makes winter navigation extremely expensive. Considerable saving could be made by e.g. optimising the use of satellite based ice monitoring.

OSIMS made recommendations for better ice monitoring system, including the need for a sea ice monitoring missions, improvement of ground segment, streamlining of analysis and interpretation of SAR data, secure access to EO data, more effective dissemination, fully digitised information systems onboard ships, need for new communication systems, strengthening of regional co-operation, and a need for a European sea ice forum.

Hannu Grönvall and Ari Seinä: Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland.

12. Seasonal and long-term control of the bottom water oxygen deficiency in a stratified shallow water coastal system
Hans Peter Hansen, Hanna C. Giesenhagen and Gerda Behrends

The seasonal development of oxygen concentrations in the deep water of a nearly permanently stratified station in the Kiel Bight is investigated. The deep water originates from Great-Belt/Kattegat inflows while the surface water represents mixed Baltic-Sea/Kiel-Bight water. The bottom water oxygen situation of an individual year is characterized by the apparent oxygen consumption rate from day 90 to 270. The influence of within year production and decomposition processes (phytoplankton/zooplankton/bacteria) on the bottom water oxygen deficiency is compared with effects of long-term changes of the nutrient budget. The bottom water oxygen deficiency poorly correlates with pelagic variables of the same year (winter-nutrient-concentrations, primary-productivity, etc.). For the period 1986 to 1996 good correlations were found between the deep water oxygen consumption rates and the nutrient loads of the respective previous year (expressed by precipitation and runoff). This indicates that a considerable part of a years production is transferred into the next year as particulate organic pool, accumulated in, or on top of, the sediment rather than dissolved organic substances or inorganic nutrients in the water column.

Hans Peter Hansen, Hanna C. Giesenhagen and Gerda Behrends: Institute for Marine Research Düsternbrooker Weg 20 24105 Kiel, Germany.

13. Long-distance nutrient transport and eutrophication in the Archipelago Sea, northern Baltic: a 3-D hydrodynamic model study
H. Helminen and P. Laihonen

Nutrient concentrations have raised in the Archipelago Sea during recent years. This is presumably caused by growth in the loads from agriculture, air deposition, fish farming and inflow from the Baltic Proper. The Archipelago Sea acts like a filter between the Baltic Proper and the Bothnian Sea ingesting a part of the inflowed nutrients. Previously only rough estimates on the amount of this background load have been given. In this study the amount of phosphorus and nitrogen transport from the Baltic Proper was estimated for the years 1993-1997 with the aid of a 3-D hydrodynamic model. Our model suggested that the role of background nutrient load may in certain situations be decisive in eutrophication process. On an average as much as 50 % of total phosphorus and nitrogen loads into our study area originates from the Baltic Proper and the Gulf of Finland. Yet, nutrient inflow seemed to vary a lot during open water seasons implying the use of the model in real time. By including all other local loading sources into the dynamic nutrient balance model we can calculate nutrient load and surplus at any given time concerning the Archipelago Sea.

H. Helminen and P. Laihonen: Southwest Finland Regional Environment Centre, P.O. Box 47 FIN-20801 Turku, Finland.

14. Five-year monitoring experience at the high-frequency station in the Gulf of Riga, Baltic Sea
Anda Ikauniece, Mikelis Mazmachs and Baiba Kalveka

Since 1992 the sampling of pelagic parameters was started at the high-frequency station of the Latvian national marine monitoring in the central part of the Gulf of Riga. The period of five-year work - 1992-1997 - gave us a possibility to ask, test and try to answer - could this station be a representative one for the hydrobiological parameters of the Gulf. The obtained data sets on phytoplankton, chlorophyll a and mesozooplankton were compared with data from other 8-10 monitoring stations. Simultaneously sampled hydrological and hydrochemical parameters were also included in the analysis.

Analogous hydrological conditions and distribution of hydrochemical variables over the whole Gulf were characteristic for winter season, except the station under obvious influence of Baltic seawater inflow. The environment situation during other seasons differed in various parts of the Gulf.

The phytoplankton biomass distribution mostly followed the pattern of abiotic parameters although species composition did not fluctuate considerably. The statistical analysis of mesozooplankton abundance data did not show any significant differences in spatial distribution in the open parts of the Gulf.

Thus, veritable results of phytoplankton species composition and mesozooplankton for the open part of the Gulf can be obtained from the high-frequency station. However, the coastal zone (up to 12 m depth) pronounced differences for all parameters.

Anda Ikauniece, Mikelis Mazmachs and Baiba Kalveka: Institute of Aquatic Ecology, University of Latvia, 8 Daugavgrivas str. LV-1007 Riga, Latvia.

15. Phytoplankton assemblages in relation to an arctic fjord environment in summer
Alexander Keck, Józef Wiktor, Ryszard Hapter and Rune Nilsen

Phytoplankton composition, abundance and distribution were studied in summer 1996 along a transect in Kongsfjorden, a high arctic fjord located at the north-west coast of Spitsbergen (79° N). Kongsfjorden is an open fjord influenced by temperate oceanic waters from the North-east Atlantic as well as freshwater and sediment discharges from adjacent glaciers. A major impact is caused by Kongsvegen, a retreating tidewater glacier at the south-west head of the fjord.

At outer and intermediate fjord locations the phytoplankton composition was dominated by the chrysophycean Dinobryon balticum reaching abundances of 2-4 * 106 cells/dm³. Associated phytoplankton, with a share of 15-20 % and typically for summer, consisted mainly of dinophyceans, cryptophyceans and indetermined flagellates, the latter of which probably with a significant part of heterotrophs. Diatoms occurred in appreciable amounts only at the outermost of the studied fjord sites (2 * 105 cells/dm³). Close to the front of Kongsvegen all of the encountered higher taxa showed strongly reduced abundances while chrysophyceans were missing. At more distant sites from the glacier (mainly inner fjord basin) the numbers of flagellated groups were comparable to those of the outer fjord area except for D. balticum which contributed a much smaller share here.

Examination of taxa abundances by cluster analyses and MDS ordination revealed that similarities between sites and depths could not be ascribed to the effects of meltwater turbidity (measured as beam attenuation) or PAR (photosynthetically available radiation) transmission.

Alexander Keck, Józef Wiktor and Ryszard Hapter: Institute of Oceanology, Polish Academy of Sciences, Powstanców Warszawy 55, PL-81-712 Sopot, Poland.

Rune Nilsen: Bodø College, Bodø, Norway.

16. Gas bubble concentrations measured acoustically in the Baltic Sea
Zygmunt Klusek and Jaromir Jakacki

Subsurface bubbles are now recognised as one of the main factor in the process of gas exchange between the atmosphere and the oceans. Rising bubbles induce a flotation process and complicate the environmental conditions in the sea surface microlayer. The level of salinity and chemical composition of sea water influence the bubble formation and must be accounted for in extrapolating results observed for salt oceanic water vs. the low saline Baltic Sea water.

Experimental data are presented on the concentration of air bubbles and their statistical distribution with respect to size obtained during a study of bubbles at depths of 1-6 m and a wind speed of 0-11 m/s. The measurements were performed in the spring periods of 1995, 1997 and 1998 in the Gdansk Deep area.

Bubbles in three size ranges, with the radii around 25, 50 and 100 micrometers were measured by a multifrequency acoustical system which has been applied to make in situ registration of underwater gas bubble populations.

A dependence of the averaged in the subsurface layer bubble concentrations on the wind have been estimated and a correlation with wind speed was established.

The results suggest not only a coupling with the wind but with other mixing processes, such as Langmuir circulation or inertial currents that distribute patches of the bubble populations.

An entrainment depth of bubbles and a function of the gas bubble concentration with respect to the depth were also determined.

Zygmunt Klusek and Jaromir Jakacki: Institute of Oceanology, Polish Academy of Sciences, ul. Powstañców Warszawy 55, PL-81-712 Sopot, Poland.

17. Small scale distribution of zooplankton around drifting buoy in central Baltic
Alexandr Korshenko

About thirty stations were made around drifting buoy in the Central Baltic during one day at summer time (22.07.1988). The buoy was used as a movable centre of co-ordinate for stations placed around in the regular spiral grid. The distance between stations varied about 1-2 n.m. Zooplankton samples were taken by Juday net with 160 mkm mesh size from upper layer 0-3m and below up to thermocline observed at horizons 18m. Bosmina was the dominant in the community. Their concentration in the surface layer were in average few times more then below. Different age stages of Acartia, cladocerans Evadne and Pleopsis, and larvae of benthic invertebrate were the subdominants. All this groups were slightly more abundant in the lower level. Horizontal distribution were very "patchy" practically for all groups of zooplankters in both layers. The "patches", with abundance of certain group 3-5 times higher then around, usually occupied in space few n.m. The "patches" of different groups overlaped only partly. Very often the animals of one group distributed in a different manner in upper and lower layers. It seems that correlation in abundance and formation of "patches" of many groups except adult crustaceans caused by local dynamical processes.

Alexandr Korshenko: State Oceanographic Institute, Kropotkinski per., 6, 119838 Moscow, Russia.

18. Is Prymnesium parvum toxic for copepods? - Grazing, egg production and egestion of a calanoid copepod Eurytemora affinis in mixtures of ‘good’ and ‘bad’ feed
Marja Koski, Mirja Rosenberg, Markku Viitasalo, Sanna Tanskanen and Ulla Sjölund

The potentially toxic, bloom-forming prymnesiophyte Prymnesium parvum was offered to copepod Eurytemora affinis as sole food and in mixtures with green algae Brachiomonas submarina and chrysophycean Pseudopedinella sp. Filtration, ingestion and egg and fecal pellet production were measured. In addition, copepods were videofilmed to check their condition and possible changes in feeding behaviour due to different food species.

With both B. submarina and Pseudopedinella sp. as sole food, filtration, ingestion, egg production and egestion of E. affinis were relatively high, and mortality low. With P. parvum as the only food, egg production and egestion of E. affinis were near zero, animals were feeding inactively and mortality was high. However, when P. parvum was mixed with other species (1:1), egg production was equally high (P. parvum + Pseudopedinella sp.), or even higher (P. parvum + B. submarina) than with Pseudopedinella sp. and B. submarina alone. Also mortality of E. affinis in mixtures of food was low.

It is concluded that P. parvum is harmful for E. affinis if it is ingested in large amounts. However, if P. parvum is added to a single species diet it may even increase the production of E. affinis. This may be due to P. parvum containing certain nutritionally important components, lacking from e.g. green algae.

Marja Koski, Markku Viitasalo and Sanna Tanskanen: Tvärminne Zoological Station, FIN-10900 Hanko, Finland / Department of Ecology and Systematics, Division of Hydrobiology, University of Helsinki, Box 17, FIN-00014 University of Helsinki, Finland.

Mirja Rosenberg: Finnish Institute of Marine Research, P.O. Box 33, FIN-00931, Helsinki, Finland.

Ulla Sjölund: Tvärminne Zoological Station, FIN-10900 Hanko, Finland.

19. Phytoplankton - the main factor responsible for transport of PAHs from water to sediments in the southern Baltic ecosystem
Grazyna Kowalewska

Twelve unsubstituted polynuclear aromatic hydrocarbons (PAHs) and phytoplankton pigments were determined by a diode-array HPLC method in samples of plankton and recent (0-1, 1-5 and 5-10 cm surface layer) sediments collected at 12 stations of the different regions of the southern Baltic and at 3 stations in the Oder Estuary (Szczecin Lagoon), in the years 1994-1996. Comparison of the correlation coefficients for PAHs concentration with phytoplankton pigments and organic carbon in the altic sediments indicate that phytoplankton is the factor principally responsible for the transport of PAHs from the water to sediments. In addition, the results for the Oder Estuary suggest that PAHs are scavenged from the water column mainly by living phytoplankton cells.

Analyses of plankton samples show that PAHs are selectively sorbed from water by phytoplankton, depending not only on their physico-chemical properties like solubility but also on their molecular structure. All these conclusions prove that phytoplankton plays a decisive role in transport and distribution of PAHs in the southern Baltic ecosystem.

Grazyna Kowalewska: Marine Pollution Unit, Institute of Oceanology, Polish Academy of Sciences, ul.Powstañców Warszawy 55, PL-81-712 Sopot, Poland.

20. Vertical distribution of heavy metals in sediments of the Gulf of Riga and of the mouths of Daugava and Lielupe
Irina Kulikova and Zinta Seisuma

Sediments can reflect the current quality of an environment as well as provide a history of the chemical parameters. In the Gulf of Riga the sediment cores was sampled during spring, summer and autumn in 1994 and 1996, but in the mouths of Daugava and Lielupe in 1996.

For estimation of heavy metal concentrations atomic absorption spectrophotometry was used. Different parts of the Gulf represented the next stations: stations under the impact of the inflow of the river estuaries, stations, where bioturbations change the original geochemistry, stations which are in the central part of the gulf.

The concentrations of Hg, Cd, Pb, Cu, Zn, Ni, Mn in sediments of the Gulf of Riga and of the rivers mouth show decrease from the top of core towards to the down. The distribution of heavy metals in cores of the Gulf of Riga and of mouths of Daugava and Lielupe is different. Only in cores from central part of the gulf every metal has high correlation with other metals. Total C correlate very good with Hg, good with Cu, Zn and with Cd and Pb significant only on level 0.05. Total N correlate good with Hg, but with Cu and Zn correlate significant only on level 0.05 In sediments of the other part of the gulf and mouths of rivers correlation between metals, metals and C are weak.

The each heavy metal has seasonal changes that are different in the Gulf of Riga and river mouths. The regional changes of heavy metals in sediments are connected with pollution sources that each place has and type of sediment.

Irina Kulikova and Zinta Seisuma: Institute of Aquatic Ecology, University of Latvia, 3 Miera Str, Salaspils, LV-2169, Latvia.

21. Influence of hydrography on microbial dynamics in the river Guadiana in southern coast of Portugal
Jorma Kuparinen, Helena Galvão, Ana Barbosa, Pedro Mendes and Margarida Reis

The Guadiana is a Mediterranean river that is part of the border between Portugal and Spain. Its basin is the fourth largest one in the Iberian Peninsula (ca. 67 000 km²). Monthly mean river flow varies markedly depending on the season and on the year. River flow 60 km upstream can reach 200 to 600 m³/s in the winter and decrease to 0.1-20 m3/s in the summer depending on rainfall. Thus, the toe of the saltwedge can oscillate between 60 km upstream and river mouth. In drought years, extensive cyanobacteria blooms have developed during summer in freshwater and have been linked to fish mortality.

Hydrographic conditions create distinct biological zonation along the river reach. Preliminary observations suggested a predominance of pigmented nanoflagellates in the river mouth and a mixture of diatoms and colony-forming cyanobacteria in the freshwater zone, some 30 km upstream. The turbidity maximum was characterized by heterotrophic processes with high bacterioplankton standing stocks and low growth efficiency. The short term variability studies suggest that bacterioplankton process variability is linked with the spatial scale of mixing rather than seasonal or geographical (study area) scales. The preliminary observations emphasise of the strong physical forcing on microbial ecology in the narrow and relatively shallow river Guadiana, the tidal phase determining the amplitude of mixing and rainfall (season) the spatial appearance of maximum mixing along the river (e.g. maximum turbidity area). The different scales of physical forcing in the mouth area and in the river reach sets constrains for the sampling strategy and data assimilation.

Jorma Kuparinen: Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland.

Helena Galvão, Ana Barbosa, Pedro Mendes and Margarida Reis: Universidade do Algarve, P-8000 Faro, Portugal.

22. Role of the temperature factor for the intensiveness of production-destruction processes in brackish water ecosystems of south and arctic seas
Nataliya Lapina and Alina Agatova

Biochemical studies of the marine ecosystems comprise aspects of spatial and temporal variability of dissolved and particulate organic matter (OM), as well as estimation of the rates of OM changes and regeneration of nutrients. The rates of OM changes were estimated by the activity of enzymes of various classes of mezo- and microplankton.

Our comparative studies of brackish water ecosystems in the south seas (the Black and Caspian Seas) and arctic seas (the White Sea) have shown a considerable variability in the activity of both hydrolytic, and oxidation and reduction enzymes under temperature in situ deviation in a narrow range. This effect has been observed for the enzyme of alkaline phosphatase, which catalyzes the hydrolytic splitting of phosphate from phosphorus organic compounds, and for the enzymes of the electron-transport system (ETS), which drive the reaction of oxygen consumption.

Studies of temperature dependence of the rates of reactions catalyzed by these enzymes in the south seas have shown that during the summer period, the dependence follows the Arrenius rule in the range of 10-25 °C, and the value of energy activation (Ea)of the reactions, catalyzed by the mentioned enzymes, varies within 12-14 kcal/mole, while in winter, significant deviations from the rule occur due to the dramatic drop of the Ea values. In the arctic seas, it is possible to observe regular deviations from the Vant-Goff rule (Q10=2). The Ea values were low (Ea= 3-6 kcal/M) which drove active metabolism of hydrobiota in cold waters.

Thus, the Ea decline of a whole range of reactions due to the change of the activity of respective enzymes could be treated as a universal mechanism of hydrobiota adaptation to the temperature changes in the habitat.

Nataliya Lapina and Alina Agatova: Russian Federal Research Institute of Fisheries and Oceanography, 17-a V. Krasnoselskaya, 107140 Moscow, Russia.

23. Seasonal fluctuations in growth, metabolism and chemical composition of some important macrozoobenthos species in the Gulf of Riga
Kari Lehtonen, Hans Cederwall and Vadims Jermakovs

Seasonal and spatial variations in growth, productivity and the physiological condition of some dominant zoobenthic species in the Gulf of Riga (Monoporeia affinis, Pontoporeia femorata [Crustacea], Marenzelleria viridis [Polychaeta] and Macoma balthica [Mollusca]) were investigated. Compared to a deeper offshore location (G5) inhabited by P. femorata, M. affinis at a shallower nearshore location (G1) exhibited slower growth, lower individual weight and a lower ammonia excretion rate throughout the year, indicating poor availability of high-quality food. Furthermore, variability in seasonal dynamics in chemical constituents (lipids, carbon and nitrogen) of the animals indicated different nutritional conditions between the study locations. At station G5, lateral transport of particulate organic matter from adjacent areas is likely to extend the period of quality food availability, while the benthos at G1 seems to be primarily fuelled by sedimentation of the spring bloom. Growth and production of M. viridis at stations G1, G5 and another offshore station (T3) took place mainly during summer-autumn, being highest at station T3. During that period, the older generations increased their individual weight more than 4 times at station G1, while the oldest M. affinis barely doubled their weight; this suggests that M. viridis is a better competitor for food. M. balthica collected from 5 stations around the gulf showed substantial variability in body composition. As a common feature, the clams contained high lipid levels, especially in the western part of the gulf. The results obtained give indications of the generally eutrophicated state of the Gulf of Riga benthic environment

Kari Lehtonen: Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland.

Hans Cederwall: Department of Systems Ecology, Stockholm University, S-10691 Stockholm, Sweden.

Vadims Jermakovs: Institute of Aquatic Ecology, Latvian University, Miera str. 3, LV-2169 Salaspils, Latvia.

24. Distribution and massbalances of metals in surface sediments of the Gulf of Riga (the Baltic Sea)
Mirja Leivuori, Irina Kulikova, Zinta Seisuma, Valter Petersell, Kestutis Jokšas, Birger Larsen, Britta Pedersen and Heldur Keis

In the Gulf of Riga 16 sites in the accumulation areas and surface sediments from 58 sites in the non-deposition areas north of 58 N were sampled during 1993-1996 to study the part of sediments on heavy metals accumulation. Samples were analyzed for total content of carbon, cadmium, lead, copper, zinc and mercury. Additional sediment data of 64 stations from Lithuania were incorporated from 1991. Distributions of elements are discussed for data of 0-5 cm sediment samples and for massbalances only the topmost first centimeter is considered. The relative highest concentrations of mercury are found in the deepest mud accumulation bottoms and in the southern near-shore areas. Distribution of cadmium is scattered having the relative high values in the coastal areas and deepest areas of the Gulf. Lead seems to be widespread over the depth range 40-50 m, while zinc and copper are quite evenly distributed over the Gulf. The concentrations of metals in the surface sediments of the offshore in the Gulf of Riga are low and comparable to those found in the rest of the Baltic Sea in similar settings. Estimations of massbalances indicates that cadmium, zinc, copper and mercury are the most mobile elements to transport outside of the Gulf, while almost half of lead loads seem to retained into the bottom sediments of the Gulf. The main uncertainty of the budgets seems to be the uncertainty in the concentrations in the water-exchange with the Baltic Sea.

M. Leivuori: Finnish Institute of Marine Research, P.O. BOX 33, FIN-00931 Helsinki, Finland.

I. Kulikova and Z. Seisuma: Institute of Aquatic Ecology, University of Latvia, 3 Miera Street, Salaspils, LV2169, Latvia.

V. Petersell: Geological Survey of Estonia, 80/82 Kanaka tee, Tallinn EE0026, Estonia.

K. Jokšas: Institute of Geography, Akademijos 2, Vilnius 2600, Lithunia.

B. Larsen: Geological Survey of Denmark and Greenland, Thoravej 8, DK 2400 Copenhagen NV, Denmark.

B. Pedersen: Danish National Environmental Research, P.O. BOX 358, DK 4000 Roskilde, Denmark.

H. Keis: Institute of Physical Chemistry, University of Tartu, Jacobi 2, EE2400 Tartu, Estonia.

25. Operational environment monitoring and information system for the Gulf of Finland, the Baltic Sea
Juha-Markku Leppänen, Eija Rantajärvi, Seija Hällfors, Mikaela Ahlman and Urmas Lips

Environmental conditions in the brackish-water ecosystem of the Gulf of Finland are affected by various factors. The fresh-water input, especially into the easternmost part, and the input of saline water to the westernmost part, create dynamic salinity patterns. The area has eutrophied during the last decades with large regional variation. Plankton biomass has increased and toxic phytoplankton blooms are common. At the same time alien species have invaded the area. Some of them may form a potential risk to the ecosystem and for the economic use of the sea.

Three countries, Finland, Estonia and Russia regularly monitor the state of the Gulf ecosystem. The traditional monitoring programmes have proved to be unreliable in detecting rapid changes in the ecosystem, e.g. toxic blooms of phytoplankton and marked regional variations. A new, effective, interdisciplinary, and target oriented monitoring programme has been created combined with an rapid information exchange network to provide comprehensive information on the state of the Gulf of Finland for environmental management purposes.

In the current paper, the monitoring and information system will be presented with examples.

Juha-Markku Leppänen, Eija Rantajärvi and Seija Hällfors: Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland.

Mikaela Ahlman: Uusimaa Regional Environment Centre, P.O. Box 360, FIN-00521 Helsinki, Finland.

Urmas Lips: Estonian Marine Institute, Paldiski Str. 1, EE0001 Tallinn, Estonia.

26. The structure of benthic littoral communitites of west Estonian archipelago area as a reflection of unique hydrodynamical conditions
Georg Martin and Henn Kukk

The inner sea area of west Estonian archipelago is characterised by unique geomorphologic and hydrodynamic conditions. The relatively high fluctuations of salinity as well as nutrient levels are caused by wind induced movements of water masses between three different water bodies: highly eutrophied Gulf of Riga, "Oligotrophic" Baltic Proper and the Gulf of Finland. The shallowness of the area enables of the development of autorophic benthic communities all over the Väinämeri area while the dominating soft bottoms put a certain limit of distribution of submerged macrovegetation. Benthic littoral communities of this area are characterised by very low species diversity of both macrovegetation and macrofauna with relatively high biomass and production. Unique complex of environmental conditions have forced the development of specific adaptations such as loos forms of macrovegetation. During last four years, the benthic littoral communities of the inner sea of west Estonian archipelago were studied intensively in terms of species composition and biomass distribution of both benthic algal and animal communities. Obtained results show great differences of functional and qualitative structure of benthic communities in comparison with other areas of the Baltic Sea. Results of multivariate statistical analyse point to the highly dynamic hydrological regime of the area to be the cause of the specific structure and morphological adaptations of benthic biota in the area.

Georg Martin and Henn Kukk: Estonian Marine Institute, Rävala 8, EE0001 Tallinn, Estonia.

27. Winter flounder (Pleuronectes americanus) from the anthropogenically-impacted western Long Island Sound, NY (USA) : respiratory responses and adaptations to hypoxia
Maryann McEnroe and Don Krozlowitz

Juvenile winter flounder, Pleuronectes americanus, utilize hypoxia-prone nearshore habitats as nursery and feeding areas yet little is known about their reactions to hypoxia, nor the consequences for habitat utilization. We investigated the respiratory and behavioral responses of juvenile (YOY) winter flounder to progressive hypoxia. The measurements included: a) opercular ventilation rate; b) frequency of aquatic surface respiration; c) frequency of air gulping; d) swimming activity, in horizontal and vertical planes; e) percent time spent at the surface. Fish were maintained in aquaria with typical summertime conditions. Oxygen concentration of the water was gradually lowered by bubbling N2 into the tank, from normoxic levels to 1 mg O2/l. Flounder ventilation rates increased steadily as DO declined, but when DO fell below 2 mg O2/l ventilation rate declined. In moderate hypoxia, about 4 mg O2/l, flounder were restive and characteristically raises their heads off the bottom. As hypoxia progressed, flounder frequently swam up to the surface and exhibited air gulping behavior. Swimming activity changed little from normoxia down to 4 mg O2/l. At 3 mg O2/l and lower, a sequence of response was initiated: at 3 mg O2/l the amount of swimming activity increased (perhaps an escape response), at 2 mg O2/l fish started to gulp air, and at 1 mg O2/l the flounder had become pale, were ventilating heavily, and had become quiescent. The possible adaptive significance will be discussed in relation to the respiratory needs and survival of small flounder in nearshore habitats of the Sound.

Maryann McEnroe and Don Krozlowitz: Division of Natural Sciences, Purchase College Purchase, NY 10577-1499, USA.

28. Dynamic of river plumes in the Pomeranian Bight
V. Mohrholz, H.U. Lass and A. Mutzke

In contrast to the ocean where river plumes are controlled by tide currents and the coriolis force mainly, we have investigated the dynamic of river plumes in a tideless and wind forced estuary of the Baltic Sea. The Oder is the main source of fresh water in the western Baltic. Due to the buffering of river discharge in the Stettin lagoon the pulslike inflow of fresh water into the Pomeranian Bight produced well separated plumes. The structure of the plumes is mainly controlled by geostrophical adjustment and the water exchange regime between the Lagoon and the Bight, whereas the direction of the plume propagation depends on the wind forced coastal dynamic.

CTD- and ADCP-measurements were carried out in the Pomeranian Bight during the TRUMP-Expeditions from 1993 to 1996. Basically differences were observed in the development of river plumes for westerly and easterly wind forcing. The freshwater was transported in a small stripe at the polish coast with westerly winds. During east wind situations stable plumes were established in the western part of the Bight. With the estimation of geostrophical current components from the observed density field the ADCP-current measurements were splitted in wind- and density driven currents. The influence of topographical features was described.

Numerical modelations with a 3D-hydrodynamical model were carried out for typical forcing conditions. The results were compared with the observations.

Volker Mohrholz, Hans Ulrich Lass and Andreas Mutzke: Baltic Sea Research Institute, Warnemünde, P.O. Box 30 10 38, D-18119 Warnemünde, Germany.

29. Chlorophyll in the White Sea
Nataliya Mordasova

Studies of the phytopigment content in the White Sea are scarce, in some bays the data are restricted to only several stations. During the complex expedition on the R/V Ivan Petrov (June-July, 1991), studies of oceanological parameters were supplemented by measurements of chlorophyll "a", "b", "c", and phaeophytin "a". The chlorophyll "a" concentrations were measured continuously with the help of the fluorometer "Aquatraka" attached directly to the oceanological zonde "Neil Brown" at 140 stations. Chlorophyll "a" was determined on the intensity of fluorescence in live cells. At complex stations, the spectrophotometry was used to determine the content of chlorophyll "a", "b", "c", and phaeophytin "a" at the sea surface and at the horizons with extreme characteristics, according to the data of the zonde.

Detailed study of the spatial distribution of phytopigments both in bays, and in open sea showed that during the period of studies, the chlorophyll content was several times higher than that obtained by other workers for the same period. The measured values (>1 mg/m³), as a rule, significantly exceeded the chlorophyll content characteristic for the highly productive waters of the World ocean. The maximum content of chlorophyll "a" was observed in Dvina Bay where the values made up to 15.5 mg/m³ in the surface layer, and, in the photic layer of 2-5 m, the total value was 40-50 mg/m². The minimum content (0.9 mg/m³) occurred in Onega Bay. According to the zonde data the vertical distribution of chlorophyll "a" had two maxima with one of them outside the photic layer. Both maxima were areas of live cells accumulation; the content of phaeophytin "a", product of chlorophyll "a" destruction, made up 50-60 % of their summed content.

The chlorophyll concentrations obtained on using the zonde equipment in the summer of 1991 allow us to determine the White Sea as a eutrophic basin.

Nataliya Mordasova: Russian Federal Research Institute of Fisheries and Oceanography, 17-a V. Krasnoselskaya, 107140 Moscow, Russia.

30. Modelling the physical processes of the Gulf of Finland by using two-and three-dimensional hydrodynamic models
Kai Myrberg

Two-and three-dimensional models have been used for the studies of the physics of the Gulf of Finland. The model simulations have been especially focused on studying salinity and temperature, but also currents, water levels and the thickness of the upper mixed layer have been included. The simulated years, for which verification material exists, are 1992 and 1994-1995. The monthly mean simulations of salinity (for 1992) by the two-dimensional model showed the highly baroclinic nature of the Gulf, with large related horizontal gradients of salinity (frontal areas). The accuracy of the model simulations was good and the location of the fronts was correct. The seasonal time evolution of the upper layer temperature was forecast quite accurately. The current simulations showed the strong coupling between flow field and high salinity gradients, supporting the idea of a baroclinic circulation. The use of the space-dependent wind and temperature fields from the atmospheric HIRLAM (High Resolution Limited Area Modelling) model clearly reduced the errors in the prognosed surface salinity compared with simulations, in which the atmospheric forcing was derived from observations from a single station. The surface temperature simulations did not show a corresponding improvement in the case of HIRLAM forcing due to the inaccuracies in the atmospheric temperature field. The control simulation for 1994-1995 showed that the two-dimensional model can reproduce surface salinity accurately during the spring-autumn period. The temperature simulations showed, however, that the spring and autumn cases, when the mixed layer is developing, cannot be described accurately by the two-layer model. The three-dimensional model results were more accurate than these results of the two-dimensional model. The present resolution of the sea model as well as of the meteorological models should be improved. Then, such features as upwelling, the dynamics of small-scale vortices and coastal-open sea interaction can be modelled. The sea model also needs high-resolution measured data for verifications of these meso-scale processes. The sea models’ capability to accurately simulate physical processes is important for ecological models too, as these need detailed physical forcing. Hence measurements, modelling and up-to-date knowledge of the sea-area studied must be closely linked.

Kai Myrberg: Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland.

31. Food consumption by clupeids in the central Baltic: Is there evidence for Top-down control?
C. Möllmann and W.F. Köster

There have been considerable changes in the pelagic ecosystem of the central Baltic Sea during the last decade. Due to a combination of anthropogenic influence (high fishing pressure) and climate induced variations in the physical environment (lacking inflows from the North Sea), the cod (Gadus morhua) stock as the Top-predator in the system was reduced from high levels in the early 1980ies to its lowest stock size on record in 1992. The preferred prey species sprat (Sprattus sprattus) showed a significant increase in population size since the late 1980ies to highest levels on record in most recent years, indicating a Top-down control within this gadoid/clupeid interaction. On the contrary, herring (Clupea harengus) did not show any evidence for a similar response to cod stock fluctuations.

The present study investigates whether fluctuations in stock sizes of clupeids cascade down to the trophic level of mesozooplankton, being their main food item. On basis of the International database on stomach contents of herring and sprat in the Baltic, individual daily rations were estimated using an exponential gastric evacuation model incorporating actual ambient temperatures. In combination with stock sizes derived by Multispecies Virtual Population Analysis (MSVPA), daily consumption rates by both clupeid populations were calculated for the period from 1978 to 1990. The analysis was performed for ICES subdivisions 26 & 28 separately and allowed an investigation of possible seasonal and interannual influences of clupeid predation on species composition and standing stocks of mesozooplankton.

Necessary future actions to investigate these Top-down control processes are identified and discussed.

C. Möllmann and F.W. Köster: Institute of Marine Sciences, Dept. of Fishery Biology, Düsternbrooker Weg 20, D-24105 Kiel, Germany.

32. Production-destruction processes in the White Sea
Irena Naletova and Victor Sapozhnikov

The primary production (PP) and destruction processes (apparent utilization of oxygen) were determined during the complex expedition on board the R/V "Ivan Petrov" in June-July, 1991. The measurements were made with the dark bottles method with oxygen modification at 29 stations over the White Sea basin. In June-July, the values of PP varied in the broad range of 0.3-2.8 g C/m²day. The oversaturation with oxygen was also high (103-107 %). The photic layer was depleted in nutrients, therefore the most intensive production occurred in the frontal zones and the dynamically active areas. The maximum PP values (2.2-2.7 g C/m²day) were observed at the frontal zone between the sea and brackish waters of the Dvina Bay and decreased elsewhere. A high water transparency and the width of the photic layer of 12-14 m characterized the Kandalaksha Bay, therefore the PP attained 1.2-14 g C/m²day there. The maximum PP was observed in the cyclonic eddy in the center of the bay. By the values of PP, the Onega Bay lagged behind the other bays of the White Sea. The PP values did not exceed 0.6-0.8 g C/m²day over the largest part of the bay. On the average, the summer primary productivity totalled 1.1 g C/m²day.

Our estimations showed that the winter nutrient stocks in the photic layer provided for almost 4 % of the annual production, while the flux of nutrients resulted from the oxidation of organic matter could sustain about 60 % of the annual PP. The nutrient flux from the underlying layers and the input from the terrestrial run-off provided for 36 % of the annual production. The average annual production of 200 g C/m² day estimated on the results of our measurements allowed us to conclude that only less than a half of PP was the new synthesized organic matter, the only substance and energy base for the development of hydrobiota of higher trophic layers.

Irena Naletova and Victor Sapozhnikov: Russian Federal Research Institute of Fisheries and Oceanography, 17-a V. Krasnoselskaya, 107140 Moscow, Russia.

33. Recent changes in the Gulf of Riga ecosystem as compared to the previous two decades
H. Ojaveer, A. Lankov, A. Lumberg, A. Turovski, I. Kotta, J. Kotta and M. Eero

Decline in riverine inflow, increase in severity of winters and summer water temperatures, together with remarkable increase in water salinity in the mid 1990s, characterize the abiotic environment of the Gulf in the 1990’s. These changes are generally opposite to those observed in the 1970s and 1980s.

Successful development of newcomers Cercopagis pengoi and Marencelleria viridis point to a still continuing microevolution of the Baltic biota.

The abundance and biomass of warm-water nektobenthic Neomysis relicta sharply increased (ca. 4-5 times) in the second half of the 1980s and have generally retained high values. Certain changes have also occurred in development of cold-water preferring Mysis spp. population.

Since 1974, important changes in the abundance of several fish stocks have taken place in the Gulf of Riga. Decrease in the abundance and extermination of some marine demersal and cold-water fishes has caused notable impoverishment of the fish community mostly in deeper parts of the basin from the end of the 1970’s. Changes in the abundance of freshwater fish stocks were less pronounced and some of them have recently increased in size. Compared to that during the 1980’s, the size of pelagic fish stocks (gulf herring population, sprat, sticklebacks) has improved.

Fish parasites of marine origin, especially Helminthes, Crustacea and Protozoa, dominated in fish parasitofauna during the second half of 1970’s and the first half of the 1980s. The share of parasites of freshwater origin, especially Monogenea and Ciliophora, increased during the 1980s. New increase in infestation by parasites of marine origin was recorded during the end of the 1980s and beginning of the 1990s. The characteristic features of fish parasitofauna during the 1990s are: continued depression of Monogenea and domination of larvae of helmints of birds and seals as final hosts.

Based on our recent investigations (in addition to the above-given, fish feeding and zooplankton data) it is suggested here that the Gulf of Riga ecosystem is at the moment in the transitional stage from the long-lasted stagnation period towards more marine conditions at to some extent lowered trophic level.

H. Ojaveer, A. Lankov, A. Lumberg, A. Turovski, I. Kotta, J. Kotta and M. Eero: Estonian Marine Institute, Lai Str. 32, Tallinn EE0001, Estonia.

34. The Puck Bay (southern Baltic) - fisheries management in a very specific brackish water system
Wojciech Pelczarski

The Puck Bay, the shallowest part of the Gulf of Gdansk, through limiting mixing of water masses as well as particular salinity and temperature patterns substantially differs from the rest of the Gulf. Estuarine character of the Puck Bay contributes to the great biodiversity of ichtiofauna - altogether there are at least 57 marine, freshwater, anadromous and catadromous fish species and many of them spawn there. The Puck Bay as the only sheltered part of Polish coast, was used to mariculture salmonids. The vicinity of big urban agglomeration (over 1 million inhabitants) causes that the influence of anthropogenic activities (mainly, fishing pressure and pollution) on the ecosystem is heavy and multidirectional. That implies that fisheries management must be adjusted to these specific conditions.

The amount of catches and their species composition since the 20’s as well as fisheries management with emphasis on stocking strategies for such endangered species as whitefish, sea trout and sturgeon, are examined. The present catches already indicate positive effects of stocking, nevertheless, that process should be continued in the following years.

As an example of changes of in the ecosystem, the spreading of goby Neogobius melanostomus, a new species in the Puck Bay, probably introduced from the Black Sea, is presented.

Wojciech Pelczarski: Sea Fisheries Institute, ul.Kollataja 1, P.O. Box 345, 81-332 Gdynia, Poland.

35. Fate of organic matter and nutrients along the estuarine gradient in the eastern Gulf of Finland, Baltic Sea
Heikki Pitkänen, Anna-Stiina Heiskanen, Vesa Gran and Jouni Lehtoranta

The concentrations of suspended N and P in the dissolved and particulate fractions and the downward flux of particulate matter were studied in relation to hydrography along the estuarine gradient from the river Neva to the open Gulf of Finland (GoF) during three cruises in 1995-1997. In addition, concentrations of N and P in the sediment cores and porewater, and denitrification activity in the sediment surface were measured. The total deposition and the potential diffusive load of N and P from the sediments as well as the loss of N through denitrification in the estuary and in the open eastern GoF were estimated for the spring (May), late summer (August) and winter (December) periods.

The non-conservative decline of total-N and the high settling rates of particulate organic nitrogen (PON) indicated that N was effectively lost by sedimentation in the estuary. The high settling rates of particulate total phosphorus (PTP) indicated effective deposition of P in the inner estuary, although the conservative behaviour of total-P along the estuarine salinity gradient suggested less effective trapping. While the sedimentation rates of organic matter, PON and PTP generally decreased from the inner estuary towards the open GoF, the concurrent enrichment of settled material by N in relation to P (decrease of N:P ratio) suggested more effective sedimentary loss of N than P. These results support the previously demonstrated pattern of a shift from P-limitation in the inner estuary to N-limitation in the outer estuary and in the open GoF due to the different sedimentation rates of N and P along the estuarine gradient.

The total-P concentrations in the sediments were highest in the inner estuary, decreasing towards the open GoF, while total-N concentrations showed an opposite pattern. The outflux of dissolved reactive phosphorus (DRP) and NH4-N from sediments were estimated to be lower in the well oxidized sediments of the inner estuary, increasing towards the open sea. Accordingly, the denitrification rates were highest in the oxidized sediments of the outer estuary. The bioturbation activity of benthic macrofauna appeared to have a crucial effect on the nutrient outflux and denitrification activity in the sediments.

The accumulation of nutrients in the bottom sediments was most effective in the inner estuary, although the largest deposition areas were located in the outer estuary and in the open eastern GoF. On an annual basis, the accumulation bottoms of the eastern GoF were estimated to retain roughly 70 % of the total P, and 20 % of the total N load to the area. The loss of N through denitrification was estimated to account ca. 20 % of the total N load. It is possible that additional N removal takes place on the non-depositionary (transportation) bottoms.

Heikki Pitkänen, Anna-Stiina Heiskanen, Vesa Gran and Jouni Lehtoranta: Finnish Environment Institute, P.O. Box 140, FIN-00251 Helsinki, Finland.

36. Several peculiarities of the vertical hydrochemical structure of the Baltic Sea
Victor Sapozhnikov and Irena Naletova

The winter (February, 1990) survey in the Baltic Sea made on board the R/V Professor Shtokman allowed us to analyze the vertical distribution of temperature, salinity, oxygen, phosphorus, nitrates, silicates, organic forms of phosphorus and nitrogen, and ammonia along the anaxial section.

The survey indicated the presence of the transformed North sea waters in the Bornholm basin, where the oxygen concentrations dropped down below 1.0 ml/L, and the phosphate and silicate concentrations attained 5.75 m M and >60 m M, respectively, while nitrates were <1.0 m M. The values of organic phosphorus (>0.3 m M) and ammonia (18.0 m M) made the maximum at the depth of 70-80 m and corresponded to the distribution pattern of salinity; this was the evidence of the presence of the transformed "old" North Sea waters in the bottom layer of the Bornholm basin.

The plume of the North Sea waters had not reached the Gotland basin yet, and therefore the nitrate reduction was completed: nitrates were absent below 130 m, while the ammonia concentrations started to increase sharply with depth, attaining 37 m M in the bottom layer.

The zone of oxygen and hydrogen sulphide coexistence (the C-layer) at the depths of 110-140 m revealed a sharp decline of phosphates (from 1.35 m M at the depth of 120 m to zero at the depth of 128 m), then the data showed an intermediate maximum of 0.94 m M (135 m) and a further decline down to 0.07 m M (138 m). which was followed by an increase up to 2.94 m M (140 m) and a slight fall down to 2.50 m M (150 m) with a further increase up to 9.35 m M in the bottom layer.

The alternate extreme values of the mineral and organic phosphorus in the C-layer, particularly, the intermediate maximum, do not follow the sorbtion model and want a special examination.

Victor Sapozhnikov and Irena Naletova: Russian Federal Research Institute of Fisheries and Oceanography, 17-a V. Krasnoselskaya, 107140 Moscow, Russia.

37. Sedimentation processes in the jet flow of river-lake contact zones
B. Shteinman, Y. Kamenir, T. Bergstein Ben-Dan, A. Hochman and O. Itzhak

The sediment balance in jet flows at the mouths of rivers in the Caspian Sea basin and the Jordan River near its entrance to Lake Kinneret were studied via application of dynamics equations and experimental measurements. Changes in the concentrations of the particulate matter (PM) and pollutants associated with the particles were documented along the flow. These changes are produced by two main mechanisms: PM sedimentation caused by attenuation of the jet flow velocity, and by the dilution of river water with sea water or lake water. The first process dominates in the region from the exit cross-section of the jet to the crest of the bar, and the second process dominates after the bar. Quantitative estimates of the influence of each of these processes on the dynamics of the PM, pollutants and bacteria are presented. The role of turbulence structure is analyzed for sedimentation processes. Generally, complete destruction of the river turbulence structure and its transformation into the turbulence structure of the lake or sea takes place over comparatively short distances, less than five widths of the river at the exit cross-section.

B. Shteinman, T. Bergstein Ben-Dan and O. Itzhak: Kinneret Limnological Laboratory, Israel Oceanographic and Limnological Research, P.O.B. 345, Tiberias 14102, Israel.

Y. Kamenir: Haifa University Research, P.O.B. 97, Kazrin 12900, Israel.

A. Hochman: Tel Aviv University, Life Sciences, Department of Biochemistry, Ramat Aviv, Tel Aviv 69978, Israel.

38. Northern Caspian Sea water pollution with Volga run-off in 1993-1995
Andrei Skorokhod and Lidia Lisitzyna

Volga is the main source of pollutants, that reach the northern Caspian Sea region. Station Verhneye Lebyazhye, located on the top of delta was chosen as a control point to estimate the amount of pollutants that will get into marine water. Main observations were obtained in 1993-1995.

Accumulation of pollutants and biochemical decay in delta were calculated on the basis of field measurements of main pollutants (petroleum hydrocarbons, phenols, organic matter, heavy metals) contence in the delta and in coastal waters. These calculations accounted for processes of pollutants’ sorption and transformation as well as for time it takes water to cover the distance from the top of delta to the seaside. This time equals 0,8-4,4 days depending on season and annual run-off.

Calculations have shown, that transformation of pollutants in the delta and in coastal waters strongly affects the volume of pollutants, that reach the northern Caspian Sea. Large part of pollutants, especially petroleum hydrocarbons, phenols, organic matter and suspended solids is lost while passing the delta and coastal zone.

Water near the Volga mouth can be characterized as "polluted", though we didn’t observe any considerable deterioration in recent years. Concentration of pollutants (mainly petroleum products and heavy metals) are higher in Volga-Caspian Canal. Pollution of bottom deposits varies spatially and sometimes reaches high concentrations.

Andrei Skorokhod and Lidia Lisitzyna: State Oceanographic Institute, 119838 Kropotkinskiy per., 6, Moscow, Russia.

39 Nutrient limitation in the Archipelago Sea: experimental and nutrient-ratio approaches
Janne Suomela, Harri Helminen, Kauko Häkkilä, Teija Kirkkala, Helmi Kotilainen and Pasi Laihonen

Eutrophication is the most acute environmental problem in the Baltic Sea, as well as in several other brackish water ecosystems. Determination of limiting nutrient is an essential question, when analysing factors behind eutrophication. In this work we have studied nutrient limitation in the Archipelago Sea, southwest Finland. Since there is large variation in water quality in different parts of the Archipelago Sea, the study was conducted at two different areas: coastal area around Turku represents the innermost part of the Archipelago Sea, but Maarianhamina sea-area in the Åland Islands includes both inner and outer archipelago. Both areas are influenced by diffuse load and municipal waste waters.

Nutrient limitation was studied experimentally in laboratory by manipulating nitrogen- (N) and phosphorus- (P) concentrations of water and by calculating nutrient ratios in the productive layer of the sea. The studies were conducted at two week intervals from May to September. In the Turku coastal area the most eutrofied sites close to Turku city were more often P-limited than N-limited. According to the nutrient ratios there was a trend from P-limitation to N-limitation so that the outermost and least eutrofied site was mostly N-limited. However, according to the experiments N-limitation was not as unambigious in the least eutrofied site. The Maarianhamina sea-area in the Åland Islands was N-limited most of the time. The results show that there is variation in nutrient limitation in different parts of the Archipelago Sea and that there are large and rapid changes in nutrient concentrations and nitrogen/phosphorus ratios even at one site.

Janne Suomela, Harri Helminen, Kauko Häkkilä, Teija Kirkkala, Helmi Kotilainen and Pasi Laihonen: Southwest Finland Regional Environment Centre, P.O. Box 47, FIN-20810 Turku, Finland.

40. Denitrification, pore water profiles and nitrogen fluxes in the sediment of the northern Baltic Sea
Liisa Tuominen, Kalervo Mäkelä, Hannu Haahti, Kari Lehtonen, Susanna Hietanen and Jorma Kuparinen

Pore water nutrient profiling in the top 2-3 cm of the sediment was done using a whole-core squeezer. In the Gulf of Finland (GOF), NO3- and NO2- were produced and consumed in this narrow layer. The distinct minimum of NO3- situated at the sediment-water interface at some stations, e.g. JML and GF2, indicates active denitrification and possibly uptake by microbes. In the Bothnian Sea (stn SR5), the NO3- peak was much smaller than in the GOF. At the deep stations in the northern Baltic Proper (LL17 and LL23), NO3- decreased rapidly in the top 1 cm.

On suboxic bottoms (stns JML and GF2), N fluxes were high and dominated by NH4+ efflux. On well-oxygenated bottom (SR5), N fluxes were moderate and dominated by NO3- efflux. In general, the Bothnian Sea sediments act as a source of NO3- whereas the investigated sediments in the GOF and in the northern Baltic Proper are sinks of NO3-.

The highest denitrification activity (isotope pairing method) was found in the central GOF (150-650 µmol N m-2 d-1). Benthic fauna was found to be the most significant factor affecting the rate of denitrification. As an average for the GOF, denitrification was calculated to release ca. 30 % of the external N input.

The effects of addition of algae (340 mg C m-2)and of Monoporeia affinis (1500 ind m-2) were studied in a laboratory experiment. In the cores enriched with algae, denitrification was dramatically reduced and the NH4+ efflux formed 93 % of the loss of N. In the amphipod-containing cores, the NH4+ efflux formed 62 % and denitrification 16 % of the loss of N.

Liisa Tuominen, Kalervo Mäkelä, Hannu Haahti, Kari Lehtonen, Susanna Hietanen and Jorma Kuparinen: Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland.

41. Relation between dispersal and nursery areas
Lauri Urho

When spawning concentrates eggs in certain places dispersal is essential to ensure better opportunities for the larvae to survive. Any dispersal tactic, however, is very vulnerable to risks of death. The dispersal tactics of different species of fish larvae, both marine and freshwater species, were compared. Spawning areas set the limits for dispersal, but neither the exact extention nor necessarily the direction of dispersal. For instance, the larvae of two coastal freshwater species sharing the same spawning area have different dispersal tactics. Larval ontogeny, behaviour and the environmental conditions determine the dispersal tactics, including when and how far to disperse. There are at least two different dispersal tactics: an immediate dispersal after hatching and a gradual one after a passive phase. Most pelagic and marine larvae disperse immediately after hatching. Despite the different dispersal tactics the larvae of two species may, however, end up in the same nursery area. There sometimes seems to be some variability in larval habitats within a species. Not only the larval ability to enter a nursery area but also the quality of the nursery areas have an influence on the year-class strength and population size.

Lauri Urho: Finnish Game and Fisheries Research Institute, P.O. Box 6, FIN-00721 Helsinki, Finland.

42. Concentrations of heavy metals in fishes from coastal waters around the Baltic Sea
Heinz-Rudolf Voigt

As the two mainly used fish species for monitoring regarding harmful substances in the Baltic biota, Baltic herring (Clupea harengus membras) and cod (Gadus morrhua morrhua) most certainly reflect the situation in the open sea due to their pelagic habits, the more stationary and benthic species like flounder (Platichthys flesus trachurus) and eelpout (Zoarces viviparus) have been selected to describe the situation in the coastal waters. The smelt (Osmerus eperlanus) being a more stationary species than herring, also partly competing on same food organisms although mainly feeding on benthic organisms, completes the attempt.

Material from selected and known extremely polluted and almost non affected areas as well, in Finland (mouth of the river Kokemäenjoki-Kumo, Åland Islands; Nåtö, Archipelago Sea; Nagu, Hanko-Hangö peninsula; Tvärminne), Estonia (Muuga, Vainupea, Väike väin), Latvia (Riga Bay; Kolka) and Germany (Firth of Kiel, harbour area of Kiel), was collected for heavy metal analysis regarding concentrations in both muscle tissue and internal organs, like liver, spleen, kidneys and gonads for both sexes.

The highest concentrations of mercury (Hg) in muscle tissue was recorded from flounder samples from Kokemäenjoki (mean 0.24 mg/kg f.w.).

The highest concentrations of iron (Fe) in muscle tissue was recorded from flounder from Nåtö (mean 62.1 mg/kg d.w.) and in liver from eelpout from Estonia (1298.6). Manganese (Mn) concentrations were highest in muscle tissue of smelt from Estonia (5.6) and in liver of smelt from Kiel harbour (17.5). Zink (Zn) maxima were recorded in muscle tissue from eelpout (98.4), herring (86.5), smelt (53.7) in Estonia and smelt from Kokemäenjoki (53.3) and in liver from eelpout from Estonia (141.6). For copper (Cu) the highest concentration in muscle tissue was recorded from flounder from Nåtö (4.9) and in liver the maximum was recorded from flounder from Tvärminne (3.78).

Cadmium (Cd) concentrations were remarkably high in muscle tissue from flounder from Nåtö (0.21) not to mention the extreme concentrations in liver of the same flounder (3.14) and in liver of flounders from Tvärminne (3.78)! The highest led (Pb) concentrations in muscle tissue was recorded from eelpout from Estonia (0.34) and in liver of eelpout from Tvärminne (2.17). For nickel (Ni) the maxima were recorded from muscle tissue of flounder (0.6) and smelt (0.5) from Kokemäenjoki and in the liver from eelpout from Tvärminne (0.91) and Estonia (0.92) and liver of smelt from Kiel harbour (0.85) and Kokemäenjoki (0.79) as well.

As the recorded levels of some metal concentrations are remarkably high even in areas regarded as almost virgin like f.ex. the Åland Islands the need for further and detailed investigations is obvious.

Heinz-Rudolf Voigt: Department of Limnology and Environmental Protection, University of Helsinki, P.O. Box 27, FIN-00014 University of Helsinki, Finland.

43. Relations between runoffs, salinity and zooplankton in the Baltic Sea, from monitoring towards prediction
Ilppo Vuorinen and Jari Hänninen

We have studied relations between monitoring time-series of North Atlantic Oscillation (NAO) Index and freshwater runoff, seawater salinity and zooplankton species abundance in the Baltic Sea. Earlier studies have shown that there is a lag from two to ten years between freshwater runoff to the Baltic Sea and its effects on the salinity and, subsequently on zooplankton. There also is evidence that this chain of effects is controlling even a further step in the food chain, herring nutrition and growth. We use Transfer Function (i.e. dynamic regression) Models as a tool in predicting pelagic ecosystem functioning. In forecasts with Transfer Function Models we are able to relate the response of one series to its own past values, but also to the past and present values of the other related time series by merging the basic concepts of the regression model with that of traditional ARIMA models.

Ilppo Vuorinen and Jari Hänninen: Archipelago Research Institute, University of Turku, FIN-20014, Turku, Finland.

44. Salinity, suspensions and sedimentation gradients influence on Arctic tidal flat benthos
Jan Marcin Wêslawski, Maria Szymelfenig, Marek Zajczkowski and Alexander Keck

Tidal flat at Longyearbyen, 78°N was sampled from the 4th km of it’s supplying river to the fjord basin behind tidal flat break. Amount of suspended mineral matter ranged from over 500 mg/dm in the river, to 100 mg/dm³ over the tidal flat and 10 in the fjord basin. Sedimentation rates ranged from 10 g/m²/day close to the river mouth, to 60 g/m²/day in the tidal flat and 600 g/m²/day in the fjord basin. Sharp salinity and depth gradient was observed within 500 m of the tidal flat break (from 0 to 45m depth and from 15 to 30 PSU). Nematoda-Harpacticoida ration was increasing from low to high salinity gradient, as well as the rate of macrozoobenthos biomass (from 0.1 to 10 g dw/m²). Number of macrobenthos species increased from 1 to 30 along the disturbance- sedimentation gradient.

Jan Marcin Wêslawski, Maria Szymelfenig and Marek Zajczkowski and Alexander Keck: Institute of Oceanology, Polish Academy of Sciences, Sopot 81-712, ul. Powstancow Warszawy 55, Poland.

45. Primary production and decomposition of organic matter in the epipelagic zone of the Gulf of Gdañsk, an estuary of the Vistula River
Zbigniew Witek, Stanislaw Ochocki, Jan Nakonieczny, Beata Podgorska, Aleksander Drgas and Alfred Grelowski

In different seasons of the years 1993-1997 several cruises to the Gulf of Gdañsk were performed, during which primary production, pelagic community respiration, bacterial production, biochemical oxygen demand, oxygen saturation, sedimentation rate, and benthic sediment oxygen consumption were measured. These data allowed us to make a preliminary carbon budget for the epipelagic zone of the Gulf.

Annual gross primary production was estimated at 225 gC/m², which was about 20 % higher than the average value for the period from 1966 to 1995. In spring and autumn primary production was higher than epipelagic community respiration and a relatively large proportion of photosynthetisized organic material sank down to the deeper layers and to the bottom. In the summer period however, decomposition of organic matter was higher than primary production. Besides the concurrent primary production also „stored" organic materials, i.e. allochthonous and/or accumulated since spring phytoplankton bloom, were utilized. In summer bacterial production corresponded to 20-25 % of primary production while in winter and spring only to 10-13 %. In the shallower parts of the Gulf, where maximum depths did not exceed 25 m, about 80 % of total community respiration occurred in the water column and about 20 % at the bottom.

The potentially biologically decomposable (at 20 °C) organic matter load from the Vistula River was estimated at 105,000-130,000 tC/yr, which approximately corresponded to 1/10 of primary production in the Gulf. However, at actual sea water temperatures decomposition of this material may be significantly slowed down and partly inhibited. For example, at low temperatures occurring in April, when the river discharge is usually most intensive, only 30-50 % of materials degradable at 20 °C were actually decomposed.

Zbigniew Witek, Stanislaw Ochocki, Jan Nakonieczny, Aleksander Drgas and Alfred Grelowski: Sea Fisheries Institute, Kollataja Str. 1, 81-332 Gdynia, Poland.

Beata Podgorska: Marine Biology Center, Polish Academy of Sciences, ul. Sw. Wojciecha 5, 81-347 Gdynia, Poland.


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