SW Coast Of Finland Research Articles

Ecological Monitoring of Marine Fish Farming Activities by Enteromorpha Intestinalis (Chlorophyta)

The biomass production of algae was markedly enhanced near a large fish farming establishment in the northern Baltic Sea, SW coast of Finland. The mean biomass values of the dominant filamentous green alga Enteromorpha intestinalis at sites near the fish farming establishment were 3-fold the values at the control site (160–190 g/ m2 vs. 64 g/m2). The nutrient discharges from the fish farms were reflected in the elemental contents of the algal tissues. The contents of phosphorus (mean values in the farming area vs. at the control site) were 0.30–0.33% (dry weight) vs. 0.25%,and the levels of N were 1.8–2.1 % vs. 1.6%. On the basis of the nutrient contents, nitrogen is the growth-limiting nutrient in these coastal waters. The results are thus in contrast with the commonly accepted view that the reduction of phosphorus discharges is the main objective in water management. In addition, the accumulation of zinc in the tissues of Enteromorpha appeared to be a useful indicator of fish farming activities

Bloom and toxin dynamics of Alexandrium ostenfeldii in a shallow embayment at the SW coast of Finland, northern Baltic Sea

In the past years, some coastal areas in the central and northern Baltic Sea have experienced recurrent blooms of the potentially toxic dinoflagellate Alexandrium ostenfeldii. The population dynamics and spatial distribution of the species were studied in the Föglö archipelago, a bloom area in Åland, northern Baltic Sea. During a two-year survey, cell and toxin concentrations of A. ostenfeldii were recorded in summer phytoplankton communities and related to environmental parameters. The studies revealed that A. ostenfeldii blooms were restricted to a small area in a narrow sound, where cells of this species were detected from May to September in 2009 and 2010. A. ostenfeldii proliferated to bloom concentrations (1.7–2.1×105cellsL−1) only at water temperatures around 20°C during warm periods in July and August. Abundance of A. ostenfeldii did not significantly correlate with dissolved inorganic nutrient concentrations (p=0.4–0.6) but was related to high concentrations of resting cysts in the sediment (p<0.001). The blooms were not monospecific but A. ostenfeldii was a part of a diverse productive phytoplankton community forming 30–60% of the total biomass during the abundance peaks. This study provides the first evidence of paralytic shellfish poisoning (PSP) toxins produced by dinoflagellate blooms in the Baltic Sea: PSP toxin dynamics correlated with the progression of the A. ostenfeldii bloom with toxin peaks mirroring the species abundance peaks. No other potentially toxic species were identified from the phytoplankton community. PSP toxin concentrations of up to 2.3μgL−1 measured in the A. ostenfeldii cell fraction suggest that blooms may have toxic effects on co-occurring biota.

Bloom forming Alexandrium ostenfeldii (Dinophyceae) in shallow waters of the Åland Archipelago, Northern Baltic Sea

In the past years, late summer blooms of the bioluminescent dinoflagellate Alexandrium ostenfeldii have become a recurrent phenomenon in coastal waters of the central and Northern Baltic Sea. This paper reports exceptionally high cell concentrations (10 5 to 10 6 cells L −1) of the species found during bioluminescent blooms in 2003 and 2004 in a shallow embayment of the Åland archipelago at the SW coast of Finland. Clonal cultures were established for morphological, molecular, toxicological and ecophysiological investigations to characterize the Finnish populations and compare them to other global A. ostenfeldii isolates. The Finnish isolates exhibited typical morphological features of A. ostenfeldii such as large size, a prominent ventral pore and an orthogonally bent first apical plate. However, unambiguous differentiation from closely related Alexandrium peruvianum was difficult due to considerable variation of sulcal anterior plate shapes. The Finnish strains were genetically distinct from other isolates of the species, but phylogenetic analyses revealed a close relationship to isolates from southern England and an A. peruvianum morphotype from the Spanish Mediterranean. Together these isolates formed a distinct clade which was separated from a clade containing other Northern European, North American and New Zealand populations. Toxin analyses confirmed the presence of the PSP toxins GTX2, GTX3 and STX in both Finnish isolates with GTX3 being the dominant toxin. Total relative PSP toxin contents were moderate, ranging from approximately 6 to 15 fmol cell −1 at local salinities of 5 and 10 psu, respectively. Spirolides were not detected. Salinity tolerance experiments showed that the Finnish isolates were well adapted to grow at the low salinities of the Baltic Sea. With a salinity range of approximately 6 to 20–25 psu, Baltic populations are physiologically distinct from their marine relatives. Vigorous production of different cyst types in the cultures suggest that cysts may play a crucial role in the survival and retainment of A. ostenfeldii populations in the Baltic Sea.

Biomass, composition and activity of organism assemblages along a salinity gradient in sea ice subjected to river discharge in the Baltic Sea

A study was undertaken to examine the activity and composition of the seasonal Baltic Sea land-fast sea-ice biota along a salinity gradient in March 2003 in a coastal location in the SW coast of Finland. Using a multi-variable data set, the less well-known algal and protozoan communities, and algal and bacterial production in relation to the physical and chemical environment were investigated. Also, the first coincident measurements of bacterial production and dissolved organic matter (DOM) in a sea-ice system are reported. Communities in sea ice were clearly autotrophy-dominated with algal biomass representing 79% of the total biomass. Protozoa and rotifers made up 18% of biomass in the ice and bacteria only 3%. Highest biomasses were found in mid-transect bottom ice. Water column assemblages were clearly more heterotrophic: 39% algae, 12% bacteria and 49% for rotifers and protozoa. Few significant correlations existed between DOM and bacterial variables, reflecting the complex origin of ice DOM. Dynamics of dissolved organic carbon, nitrogen and phosphorus (DOC, DON and DOP) were also uncoupled. A functional microbial loop is likely to be present in the studied ice. Existence of an under-ice freshwater plume affects the ecosystem functioning: Under-ice water communities are influenced directly by river-water mixing, whereas the ice system seems to be more independent—the interaction mainly taking place through the formation of active bottom communities.

Changes in Phytoplankton Biomass and Nutrient Quantities in Sea Ice as Responses to Light/Dark Manipulations during different Phases of the Baltic Winter 2003

The response of Baltic Sea ice communities to changing light climate was studied in three subsequent 3 week in situ experiments on the SW coast of Finland. The investigation covered three different winter periods, short day with low solar angles leading to limited light in the ice, late winter with deep snow cover and early spring with melting snow and increasing light availability. The experimental setup consisted of transparent (no snow) and completely darkened (heavy snow cover) plexiglass tubes in which the ice cores were incubated in situ from 1 to 2 weeks. Changes in the concentrations of inorganic nutrients (NO 3 − -–N, PO4 3−-–P, SiO4 −-–Si) and chlorophyll-a concentration in the phytoplankton community composition were recorded as responses to different light manipulations. Changes in inner ice light intensity in untreated ice as well as the temperature both in air and ice were recorded over the entire study period. Increased irradiance in late winter/early spring and during meltdown affected the chlorophyll-a amount in the sea ice. During these periods the phytoplankton community in the top layers decreased possibly as a consequence of photo-acclimation. Closer to the bottom of the ice, however, the increased inner ice light intensity induced algal growth. Complete exclusion of light stopped the algal growth in the whole ice column. Darkening the ice cores also slowed down the ice melting opposite to accelerated melting caused by increased light. The significant differences found in nutrient concentrations between the light and dark treatments were mostly explicable by changes in algal biomass. No obvious changes were observed in the phytoplankton community composition due to light manipulation, diatoms and heterotrophic flagellates dominating throughout the study period.

Recent Changes in Trophic State of the Baltic Sea along SW Coast of Finland

Recent Changes in Trophic State of the Baltic Sea along SW Coast of Finland

Recent Changes in Trophic State of the Baltic Sea along SW Coast of Finland

Drawing reliable conclusions on changes in the trophic state of various subareas of the Baltic Sea is problematic, in large part because the monitoring of productivity parameters exhibiting high natural variability is based on sparse sampling. This emphasizes the importance of long-term data sets. Here we present a 30-year chlorophyll alpha data set from the western Gulf of Finland. The trophic state of the study area showed an increasing trend in the 1970s and 1980s manifested mainly as strengthened vernal blooms. This trend did not continue in the 1990s, and the seasonal phytoplankton biomass maxima since then has begun to show some bias toward the late summer. The changes in seasonal maxima of phytoplankton blooms probably reflect i) decreased availability of N suppressing the magnitude of the vernal bloom, which increases the P reserves for the summer, and ii) enhanced internal P loading, which further increases the summer P reserves.

Ecto-cellular enzyme activity associated with filamentous cyanobacteria

Extra-cellular enzyme activity was investigated during a cyanobacterial bloom domi- nated by Nodularia spumigena on the SW coast of Finland, Baltic Sea. When filaments of N. spumi- gena were abundant in surface waters, alkaline phophatase (AP) activity was elevated, and ~37% of the total activity was associated with the >2 µm fraction. About 30% of the total leucine aminopepti- dase (LAP) activity was also associated with the >2 µm size fraction. When spherical aggregates con- taining a mixture of moribund and decaying N. spumigena strands mixed with other cells were abun- dant in surface waters, ~50% of the total AP activity and ~22% or less of the total LAP activity was associated with the >2 µm fraction. Both total LAP and AP activity were positively correlated with chlorophyll a. LAP activity in the >2 µm fraction was positively correlated with thymidine uptake, suggesting that much of the observed LAP activity in the >2 µm fraction was due to heterotrophic bacteria associated with cyanobacteria. In contrast, AP activity in this size fraction was not signifi- cantly associated with bacterial numbers or activity. Experiments with isolated cyanobacterial aggre- gates demonstrated that they were sites of enhanced enzymatic activity. Cultured, axenic strands of N. spumigena displayed LAP and AP activity. Our data indicate that colonies and aggregates of cyanobacteria in the Baltic Sea can be important sites of hydrolytic activity and therefore of nutrient regeneration.

Predation by the mysid shrimps Mysis mixta and M. relicta on benthic eggs of Bosmina longispina maritima (Cladocera) in the northern Baltic Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 281:155-163 (2004) - doi:10.3354/meps281155 Predation by the mysid shrimps Mysis mixta and M. relicta on benthic eggs of Bosmina longispina maritima (Cladocera) in the northern Baltic Sea Satu Viitasalo1,2,*, Markku Viitasalo3 1Department of Biological and Environmental Sciences, University of Helsinki, PO Box 65, 00014 Helsinki, Finland 2Tvärminne Zoological Station, 10900 Hanko, Finland 3Finnish Institute of Marine Research, PO Box 33, 00931 Helsinki, Finland *Email: stmviita@mappi.helsinki.fi ABSTRACT: The abundance of Bosmina longispina maritima (Cladocera), the most common water flea in the Baltic Sea, shows considerable interannual fluctuations.The number of Bosmina resting eggs (ephippia) in the sediment also fluctuates from year to year. Biotic as well as abiotic factors have been suggested to contribute to these fluctuations, but the impact of benthic predation by pelagic mysids has not yet been considered. The objective of this study was to investigate the effect of benthic predation and bioturbation by Mysis mixta and M. relicta on the ephippia of B. longispina maritima on the SW coast of Finland. The results show that mysids can significantly affect the number of Bosmina eggs in the sediment. All size groups of both mysid species preyed upon ephippia of B. longispina maritima both in the water column and directly from the top layer of sediment, whereas they rejected the eggs of another cladoceran species, Pleopsis polyphemoides. The predation rate on B. longispina maritima ephippia was significantly lower when the eggs were buried under a sediment layer of ca. 1 cm. This suggests that factors affecting the vertical distribution of ephippia in the sediment determine the magnitude of the impact that mysids have on B. longispina maritima benthic eggs. KEY WORDS: Bosmina longispina maritima · Resting eggs · Mysis mixta · M. relicta · Benthic predation · Baltic Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 281. Online publication date: November 01, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

A comparison between 1928 and 2000 indicates major changes in the macrozoobenthos species composition and abundance on the SW coast of Finland (Baltic Sea)

A comparison between 1928 and 2000 indicates major changes in the macrozoobenthos species composition and abundance on the SW coast of Finland (Baltic Sea)

Effects of toxic cyanobacteria on a plankton assemblage: community development during decay of Nodularia spumigena

We studied the development of the plankton community in an artificially created toxic Nodularia spumigena bloom during a 2 wk enclosure study at the SW coast of Finland in the Baltic Sea. We measured bacterial abundance, dominant phytoplankton groups and ciliates, as well as concentrations of phytoplankton pigments, fatty acids, nodularin, protein and nutrients. A high POC:chl a (<10 µm) ratio (427 ± 185), a decrease in the polyunsaturated:total fatty acid ratio (from 0.4 to 0.2), and a reduction in cyanobacteria filament length indicated decay of N. spumigena during the course of the experiment. Along with cyanobacterial decay, high concentrations of ammonium (last day: 2.7 ± 2.0 µmol l -1 ), nitrate (0.1 ± 0.01 µmol l -1 ), and organic nutrients were released into the water, whereas chl a and the cyanobacterial pigments, echinenone and zeaxanthin, decreased. Nodularin was found in the mesocosms during the whole experiment. A strong increase in filamen- tous bacteria was detected by the middle of the experiment, most likely indicating a response to grazing pressure. Two ciliate species, Mesodinium rubrum and Urotricha sp., decreased dramatically during the experiment, probably due to predation by the increasing mesozooplankton community. The ciliate Euplotes sp. flourished in the bags and was best suited to escape predation due to its protecting lorica and its surface affinity. No direct harmful effects of the cyano-bacteria on the microorganisms could be documented. We conclude that these blooms provide a potential food source for the heterotrophic food chain, from bacteria, flagellates and ciliates to crustacean zooplankton, and possibly fish.

Effects of cyst resuspension on germination and seeding of two bloom-forming dinoflagellates in the Baltic Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 216:57-66 (2001) - doi:10.3354/meps216057 Effects of cyst resuspension on germination and seeding of two bloom-forming dinoflagellates in the Baltic Sea Anke Kremp* Department of Ecology and Systematics, Division of Hydrobiology, PO Box 17, 00014 University of Helsinki, Finland and Tvärminne Zoological Station, 10900 Hanko, Finland *E-mail: anke.kremp@helsinki.fi ABSTRACT: The implications of cyst resuspension on germination and subsequent seeding of the 2 spring-bloom dinoflagellates Scrippsiella hangoei (Schiller) Larsen and Peridiniella catenata (Levender) Balech from the Baltic Sea were investigated in a field study and laboratory experiments. Sedimentation of resuspended cysts was monitored by an automated sediment trap in 2 consecutive winters prior to and throughout the germination period off the SW coast of Finland. The effects of increased irradiances and water motion on germination and germling survival were tested by incubating cysts at different light levels and in turbulent water. Cyst fluxes of both species were low during the calm and cold winter of 1998/1999. In 1999/2000, heavy storms caused strong resuspension of S. hangoei cysts. Light significantly increased the germination frequency of S. hangoei cysts and supported germling survival and cell division. In P. catenata, the percentage of excystment was not significantly influenced by light and germination was successfully completed in both darkness and light. Subsequent growth of the species, however, required light, although maximum cell numbers were encountered at an irradiance as low as 10 µmol m-2 s-1. Small-scale turbulence reduced the germination frequency of S. hangoei but did not affect excystment in P. catenata. No negative effects on subsequent growth were detected. The favourable effects of light on germination and germling survival of S. hangoei emphasize that resuspension would be advantageous for the bloom initiation of this species. Cyst resuspension seems to be less important in P. catenata population dynamics, since germination can be successfully completed in darkness and the amount of cysts transported to the water surface is insignificant even with strong turbulent mixing. It is concluded that cyst resuspension may be advantageous for dinoflagellate bloom initiation, depending on its extent and timing and the specific germination requirements of the respective organism. KEY WORDS: Cysts · Dinoflagellates · Germination · Peridiniella · Resuspension · Scrippsiella turbulence Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 216. Online publication date: July 06, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Sexuality and cyst formation of the spring-bloom dinoflagellate Scrippsiella hangoei in the coastal northern Baltic Sea

The temporal sequence and the magnitude of the sexual reproduction and subsequent cyst deposition of the common spring-bloom dinoflagellate Scrippsiella hangoei (Schiller) Larsen was studied during spring 1996 on the SW coast of Finland, Baltic Sea. The abundances of the different size of fractions of S. hangoei (14 to 18 μm, 18 to 22 μm and >22 μm) were monitored in the water column, and the deposition of resting cysts was measured using moored sediment traps. Cyst sedimentation rates were measured throughout the seasonal cycle in order to estimate cyst resuspension rates for the quantitative assessment of the fraction of population undergoing encystment. The onset of sexual reproduction, indicated by a significant increase of the small cells (14 to 18 μm) representing gametes, occurred in a nutrient replete environment well before the exponential growth phase and peak abundances of vegetative cells. Gamete formation was followed by high abundances of large cells (>22 μm) representing planozygotes, and subsequent sedimentation of resting cysts. Approximately 60% of the asexually growing bloom population was estimated to form planozygotes, suggesting that encystment was an important factor in bloom termination and possibly plays a role in the regulation of the magnitude of the bloom. Finally encystment accounted for 40% of the entire S. hangoei population, resulting in a considerable loss of the bloom population and an input of the vernal phytoplankton biomass to the benthos.

Short communication. Carbon:nitrogen ratios of Baltic Sea copepods-indication of mineral limitation?

The carbon (C) and nitrogen (N) content and the C:N ratio of two common calanoid copepods, Eurytemora affinis and Acartia bifilosa, were measured during spring and summer at the SW coast of Finland, northern Baltic Sea. The C:N ratio of both copepod species was low and stable (4-4.5), irrespective of sampling time, which implies N limitation at least during intermediate to high food concentrations in spring and early summer. In addition, experiments were conducted to reveal whether the diet of copepods affects their C and N content. Adding green algae Brachiomonas submarina in concentrations of 50-500 µg C l-1 to <100-µm-filtered sea water did not significantly increase copepod C or N content in 3 day experiments. However, the C and N contents of E.affinis eggs were ~2 times higher in high food concentration, which may increase survival of eggs and nauplii. The production of freshwater zooplankton is frequently shown to be limited by

Seasonal development of meso-zooplankton biomass and production on the sw coast of Finland

Abstract Seasonal development of mesozooplankton abundance, biomass and production were studied on the SW coast of Finland in three hydrographically distinct areas with different phytoplankton dynamics. In addition, the present species composition was compared to that at the beginning of the century, using a multidimensional scaling analysis. Mesozooplankton biomass and production were dominated by only a few species: the largest part of the production in the archipelago and open sea areas (11.3 g C m-2 year-1 and 28.1 g C m-2 year-1, respectively) consisted of that by raptorial and suspension-feeding calanoid copepods (Acartia bifilosa and Eurytemora affinis) and of that by rotifers (Synchaeta baltica), while annual mesozooplankton production in the bay area (10.5 g C m-2 year-1) was mainly due to production of filter-feeding cladocerans (Daphnia cucullata and Bosmina longispina) and predatory cyclopoid copepods (Thermocyclops oithonoides). The food chain in the bay area seemed to be based on heterotroph...

Sedimentation and Pelagic Retention of Particulate C, N and P in the Coastal Northern Baltic Sea

Sedimentation and pelagic retention capacity of particulate carbon, nitrogen and phosphorus as well as the impact of resuspension and preservation on sedimentation rates were studied during spring and summer in the SW coast of Finland, Baltic Sea. Formaldehyde preservation resulted in significantly higher carbon, nitrogen and chlorophyllasedimentation rates when compared to traps without preservative. This was mainly attributable to contamination by vertically migrating micro-organisms in traps with formaldehyde and mineralization inside the non-preserved trap cylinders. During the spring bloom, stoichiometric ratios of settled and suspended particulate material indicated that phosphorus was retained in the pelagic system almost twice as effectively as carbon and nitrogen, while carbon and nitrogen were settling at equal rates. During summer, when sedimentation rates were low, nutrient ratios of settled and suspended matter indicated that both N and P were recirculated in the pelagic system more effectively than carbon while P was retained 1·4 times more effectively than nitrogen. High current velocities and increase of deep-water salinity correlated with increased sedimentation of particulate material, with low N:P, C:P and high C:N ratios indicating input of resuspended phosphorus during upwelling events. Wind velocity and direction did not have any clear relationship to the quality of settled material, denoting that wind-induced wave action and transport of littoral material had minor impact on sedimentation rates. Primary sedimentation of carbon corresponded to 57% of the total primary production during the study period from April to August, while that of nitrogen was 42% of estimated nitrogen assimilation, indicating that the overall export of carbon was more effective than that of nitrogen from the pelagic system.

Seasonal occurrence and hatching of calanoid eggs in sediments of the northern Baltic Sea

The seasonal occurrence and hatching of benthic eggs of calanoid copepods were studied for 1 yr in the surface sediments at 2 sites (a 33 m deep archipelago area and a 42 m deep site in an enclosed bay) off the SW coast of Finland, northern Baltic Sea. Eggs were abundant at both sites (up to 4 and 6 X 106 eggs m-2). At the archipelago site, most eggs belonged to Acartia bifilosa and A. tonsa; at the bay site, eggs of Eurytemora affinis and Acartia spp. occurred. At the archipelago site, the egg numbers in the surface sediment followed closely the seasonal abundance of the planktonic Acartia spp. females. The eggs collected from the sediment were Incubated at temperatures corresponding to the in situ bottom temperatures. Hatching of the A. bifilosa eggs occurred throughout the year, but it was most intensive in autumn when water stratification broke and the deep water warmed up to 13°C. It is suggested that a large number of the A. bifilosa eggs sink to the bottom prior to hatching m shallow coastal areas of the Baltic Sea. Hatching of the benthic eggs occurs throughout the year and the rate of naupliar emergence from the sediments depends on benthc condtions and processes (e.g. temperature, sediment resuspension and bioturbation). At the bay site, where the surface water layer was hydrographically separated from the deep water, the coupling between the benthic egg abundance and the planktonic populations was not so obvious. The dominant species E. affinis carries its eggs in an egg sac unhl hatching, and probably only the diapause eggs, which are produced in autumn, fall to the bottom. A. tonsa was abundant in the water column at both study sites in autumn, even outnumbering other Acartia spp. in some samples. The eggs of the species only hatched in autumn, when the incubations were conducted at 10 to 13°C. It is probable that A. tonsa spends most of the year as benthic resting eggs In the northern Baltic Sea. In contrast, A bifilosa and E. affinis occurred in the plankton in winter at both study sites, though in low concentrations. They thus have 2 possible sources of recruitment when conditions are again favourable for population growth in spring: hatching of benthc eggs and reproduction by the overwintering population.

Environmental factors affecting the occurrence of different morphological forms of cyanoprokaryotes in the northern Baltic Sea

Cyanoprokaryotes (blue-green algae, cyanobacteria) and environmental factors were studied in the Baltic Sea, off the SW coast of Finland, from April to December 1993. The aim was to outline the seasonal development of cyanoprokaryote populations and the occurrence of species and species groups in relation to prevailing hydrographic conditions and general features of the plank- tonic community. Altogether, 27 taxa of cyanoprokaryotes were encountered, representing the orders Chroococcales, Nostocales and Oscillatoriales. Different morphological forms of cyanoprokaryo tes predominated during certain periods of the yean the spherical, gomphosphaerioid colonies of the genera Coelomoron, Coclosphaerium, Snowella and Woronichinia were rather abundant in early spring and the most abundant group in late autumn; minute-celled colonies with mucilaginous struc- tures, e.g. the genera Aphanothece, Cyanonephron, Lemmermanniella and Merismopedia, were abun- dant during early summer; and filamentous, nitrogen-fixing species in late summer and early autumn. Each of the periods represents a distinct successional phase of the planktonic community with inher- ent environmental conditions, and it was obvious that the cyanoprokaryotic assemblage was modified by the general development of the planktonic community. According to canonical correspondence analysis (CCA), temperature and the weight ratio of inorganic nitrogen to inorganic phosphorus were the most important factors explaining variation in the cyanoprokaryote assemblage.

Grazing by mesozooplankton and metazoan microplankton on nanophytoplankton in a mesocosm experiment in the northern Baltic

Grazing by two size classes of metazooplankton, mesozooplankton(Meso; >140 um in size) and metazoan microplankton (Micro; 100-140 urn in size), was studied in a mesocosm experiment carried out off the SW coast of Finland, northern Baltic Sea, in late summer. During the 3 week study, the mesocosm was manipulated periodically by the addition of nutrient (ammonium and phosphate) and fish predators (stickleback fry). During the experimental period, the mesocosm was sampled five times to measure metazooplankton grazing, using 5 um pre-filtered and l4C-labelled natural nanoplankton as food. In spite of the presence of fish, Meso biomass increased throughout the experi- mental period. The biomass of Meso was composed mostly of different copepodite stages of Eury- temora affinis and the dadoceran Bosmma longispina maritima, and that of Micro by biomass of copepod nauplii N1II-NVI. Owing to its larger biomass, Meso could exert a greater grazing pressure on the nanophytoplankton than could Micro. The biomass specific clearance rate (BSCR) was gener- ally the same for both groups, occasionally higher in Micro. The BSCR increased during the first half of the study period, after which the clearance rates were depressed, coinciding with a sudden decrease in water temperature. The daily ingestion rate on nanophytoplankton (% of biomass as carbon) varied between 3 and 96% for Meso, and between 4 and 130% for Micro. When integrated over the study period, grazing on nanophytoplankton was estimated to provide about 60% of the carbon require- ments of metazooplankton, respectively, thus, protists were probably important food. The overall gross growth efficiency for the whole metazooplankton community was estimated to be 32%. Meso and Micro grazing was estimated to account for 8 and 2% of primary production, indicating that they were not able to control phytoplankton primary production enriched by nutrient additions.

Copepod eggs survive a decade in the sediments of the Baltic Sea

Many planktonic calanoid copepod species have been proved to spend a part of their life cycle as benthic resting eggs. In addition to avoiding seasonally occurring unfavourable conditions resting stages may also be used as a long-term survival strategy. The aim of this study was to find out for how long eggs of calanoid copepods retain their viability in the sediments of the Baltic Sea. The occurrence of viable copepod eggs in sea bottom sediment was studied in Pojovik Bay, SW coast of Finland. Eggs were found throughout a 25 cm deep core but deeper than 20 cm they were very scarce. Eggs were incubated at 12 °C in order to check the viability, and their age was estimated by determining the sediment accumulation rate with 137Cs-method. Viable eggs were estimated to be 10–13 yrs old, some possibly even 18–19 yrs. Most eggs in the top 8 cm were viable, their age being up to 7–8 yrs. Nauplii that hatched from the eggs belonged to Acartia bifilosa and Eurytemora affinis, A. bifilosa dominating the hatchers of the top sedment layers and E. affinis the deeper layers. Preliminary evidence is presented that E. affinis produces true diapause eggs in the Baltic Sea.