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Spring phytoplankton blooms contribute a substantial part to annual production, support pelagic and benthic secondary production and influence biogeochemical cycles in many temperate aquatic systems. Understanding environmental effects on spring bloom dynamics is important for predicting future climate responses and for managing aquatic systems. We analyzed long-term phytoplankton data from one coastal and one offshore station in the Baltic Sea to uncover trends in timing, composition and size of the spring bloom and its correlations to environmental variables. There was a general trend of earlier phytoplankton blooms by 1-2 weeks over the last 20 years, associated with more sunshine and less windy conditions. High water temperatures were associated with earlier blooms of diatoms and dinoflagellates that dominate the spring bloom, and decreased diatom bloom magnitude. Overall bloom timing, however, was buffered by a temperature and ice related shift in composition from early blooming diatoms to later blooming dinoflagellates and the autotrophic ciliate Mesodinium rubrum. Such counteracting responses to climate change highlight the importance of both general and taxon-specific investigations. We hypothesize that the predicted earlier blooms of diatoms and dinoflagellates as a response to the expected temperature increase in the Baltic Sea might also be counteracted by more clouds and stronger winds. A shift from early blooming and fast sedimenting diatoms to later blooming groups of dinoflagellates and M. rubrum at higher temperatures during the spring period is expected to increase energy transfers to pelagic secondary production and decrease spring bloom inputs to the benthic system, resulting in lower benthic production and reduced oxygen consumption.

Assessing the relative importance of environmental conditions and community interactions is necessary for evaluating the sensitivity of biological communities to anthropogenic change. Phytoplankton communities have a central role in aquatic food webs and biogeochemical cycles, therefore, consequences of differing community sensitivities may have broad ecosystem effects. Using two long-term time series (28 and 20 years) from the Baltic Sea, we evaluated coastal and offshore major phytoplankton taxonomic group biovolume patterns over annual and monthly time-scales and assessed their response to environmental drivers and biotic interactions. Overall, coastal phytoplankton responded more strongly to environmental anomalies than offshore phytoplankton, although the specific environmental driver changed with time scale. A trend indicating a state shift in annual biovolume anomalies occurred at both sites and the shift's timing at the coastal site closely tracked other long-term Baltic Sea ecosystem shifts. Cyanobacteria and the autotrophic ciliate Mesodinium rubrum were more strongly related than other groups to this trend with opposing relationships that were consistent across sites. On a monthly scale, biotic interactions within communities were rare and did not overlap between the coastal and offshore sites. Annual scales may be better able to assess general patterns across habitat types in the Baltic Sea, but monthly community dynamics may differ at relatively small spatial scales and consequently respond differently to future change.

Scale is a key to determining which processes drive community structure. We analyse size distributions of phytoplankton to determine time scales at which we can observe either fixed environmental characteristics underlying communities structure or competition-driven size distributions. Using multiple statistical tests, we characterise size distributions of phytoplankton from 20-year time series in two sites of the Baltic Sea. At large temporal scales (5-20 years), size distributions are unimodal, indicating that fundamental barriers to existence are here subtler than in other systems. Frequency distributions of the average size of the species weighted by biovolume are multimodal over large time scales, although this is the product of often unimodal short-term (<1 year) patterns. Our study represents a much-needed structured, high-resolution analysis of phytoplankton size distributions, revealing that short-term analyses are necessary to determine if, and how, competition shapes them. Our results provide a stepping-stone on which to further investigate the intricacies of competition and coexistence., AuthorCount:7

It is commonly accepted that summer cyanobacterial blooms cannot be efficiently utilized by grazers due to low nutritional quality and production of toxins; however the evidence for such effects in situ is often contradictory. Using field and experimental observations on Baltic copepods and bloom-forming diazotrophic filamentous cyanobacteria, we show that cyanobacteria may in fact support zooplankton production during summer. To highlight this side of zooplankton-cyanobacteria interactions, we conducted: (1) a field survey investigating linkages between cyanobacteria, reproduction and growth indices in the copepod Acartia tonsa; (2) an experiment testing relationships between ingestion of the cyanobacterium Nodularia spumigena (measured by molecular diet analysis) and organismal responses (oxidative balance, reproduction and development) in the copepod A. bifilosa; and (3) an analysis of long term (1999-2009) data testing relationships between cyanobacteria and growth indices in nauplii of the copepods, Acartia spp. and Eurytemora affinis, in a coastal area of the northern Baltic proper. In the field survey, N. spumigena had positive effects on copepod egg production and egg viability, effectively increasing their viable egg production. By contrast, Aphanizomenon sp. showed a negative relationship with egg viability yet no significant effect on the viable egg production. In the experiment, ingestion of N. spumigena mixed with green algae Brachiomonas submarina had significant positive effects on copepod oxidative balance, egg viability and development of early nauplial stages, whereas egg production was negatively affected. Finally, the long term data analysis identified cyanobacteria as a significant positive predictor for the nauplial growth in Acartia spp. and E. affinis. Taken together, these results suggest that bloom forming diazotrophic cyanobacteria contribute to feeding and reproduction of zooplankton during summer and create a favorable growth environment, AuthorCount:9

The effects of an extensive bloom of the potentially toxic Prymnesium polylepis (Haptophyta) on breeding eiders (Somateria mollissima) in the Baltic Sea were analysed. Increasing abundances of the alternate stage P. polylepis was detected by a marine monitoring programme in the autumn 2007. The bloom peaked between March and May 2008 in the southern, central and northwestern Baltic Proper and abundances of up to 5 x 10(6) cells l(-1) were recorded. At several sites P. polylepis constituted between 30 and 90% of the total phytoplankton biovolume. The flagellate was only recorded in low numbers in the northeastern Baltic Proper and Gulf of Finland. The abundances were low in 2007, 2009 and 2010. In 28 eider colonies situated in the southern and central Baltic Proper, sharp and synchronous declines in the number of nesting eiders were observed from 2007 to 2008. In colonies on Gotland in the central Baltic Proper, a 76% decrease, from 6650 nests to 1620 nests, was followed by increases in 2009 and 2010, although not up to numbers observed in 2007. At Utklippan and Ertholmene in the southern Baltic Proper, the observed decreases of 55%, from 144 to 65 nests, and 36%, from 1660 to 1060 nests, respectively, between 2007 and 2008, were followed by increases in 2009 and 2010 up to the level observed in 2007. By contrast, no general decline of the number of nesting eiders was observed from 2007 to 2008 in 75 colonies in the northeastern Baltic Proper and Gulf of Finland. Hence, the spatial distribution of the P. polylepis bloom in 2008 closely matched the observed distribution of extensive non-breeding of female eiders. We suggest that the intensive spring bloom of P. polylepis, either through a toxic or non-toxic pathway, affected the main benthic food of eiders, i.e. blue mussels (Mytilus trossulus x Mytilus edulis), at pre-breeding foraging sites close to the breeding sites, and, subsequently, the body condition of adult female eiders and their breeding propensity., AuthorCount:6

A large bloom of Prymnesium polylepis occurred in the Baltic Sea during the winter 2007 - spring 2008. Based on numerous reports of strong allelopathic effects on phytoplankton exerted by P. polylepis and its toxicity to grazers, we hypothesized that during this period negative correlations will be observed between P. polylepis and (1) main phytoplankton groups contributing to the spring bloom (i.e., diatoms and dinoflagellates), and (2) zooplankton growth and abundance. To test these hypotheses, we analyzed inter-annual variability in phytoplankton and zooplankton dynamics as well as growth indices (RNA: DNA ratio) in dominant zooplankton in relation to the Prymnesium abundance and biomass. Contrary to the hypothesized relationships, no measurable negative responses to P. polylepis were observed for either the total phytoplankton stocks or the zooplankton community. The only negative response, possibly associated with P. polylepis occurrence, was significantly lower abundance of dinoflagellates both during and after the bloom in 2008. Moreover, contrary to the expected negative effects, there were significantly higher total phytoplankton abundance as well as significantly higher winter abundance and winter-spring RNA: DNA ratio in dominant zooplankton species in 2008, indicating that P. polylepis bloom coincided with favourable feeding conditions for zooplankton. Thus, primary consumers, and consequently also zooplanktivores (e.g., larval fish and mysids), may benefit from haptophyte blooms, particularly in winter, when phytoplankton is scarce., AuthorCount:3

During autumn 2007, an unusual increase in an algal species belonging to the order Prymnesiales was observed throughout the Baltic Sea Proper during routine national monitoring. Electron microscopical examination of the blooming species showed two types of flat scales - small and large - that resembled those of the alternate stage of Prymnesium polylepis. No spine-bearing scales were found. The 18S rDNA sequence data (n = 20, c. 1500 bp) verified the species identification as P. polylepis. There was up to 0.5% (7 bp) variability in the P. polylepis partial 18 S rDNA sequences from the Baltic Sea. These environmental sequences differed by 0-0.35% (0-4 bp) from cultured P. polylepis (isolate UIO036), and by 1.0-3.7% from other available Prymnesium sequences. The number of cells assumed to be P. polylepis began to increase in October 2007 coincidently with significantly calm and dry weather, and at their maximum the cells accounted for over 80% of the total phytoplankton biovolume in December-January. During February-April 2008, 95% of the Prymnesiales cells were in the size class of P. polylepis (>6 mu m). The species attained bloom concentrations (>1 x 10(6) cells l(-1)) from March to May 2008. The species was observed throughout the Baltic Sea, except the Bothnian Bay, Gulf of Riga and the Kattegat. No toxic effects of the bloom were observed., AuthorCount:10

Baltic Sea Environment Fact Sheets 2012

Svensk miljöövervakning

We investigated the distributions of the toxic dinoflagellates Dinophysis acuminata and D. norvegica in the brackish Baltic Sea, and found them to differ both regarding their seasonality and their vertical distribution. Dittophysis acuminata was considerably more abundant, especially in the Gulf of Finland, where we observed an August peak of 14 300 cells l(-1). It occurred in elevated abundances during or after periods of high phytoplankton biomass in early and late summer. Dinophysis norvegica was abundant during a shorter period, peaking one month after the first D. acuminata maximum. While D. norvegica probably is restricted by both salinity and temperature in the northern Baltic Sea, the more tolerant D. acuminata thrives. The results presented here expand the wide range of scenarios in which D. acuminata may bloom worldwide. Both species mainly formed population maxima either in the mixed surface waters or near the thermocline. Dinophysis acuminata usually occurred in the illuminated and nutrient-poor mixed surface layer, but in the presence of light and a nutricline it formed distinct subsurface peaks. Dinophysis norvegica was not as sensitive to darkness and predominantly formed subsurface peaks, even below the euphotic zone. These occurrences were promoted by shallow stratification, and the combination of a deep mixed layer and cool surface waters drew the D. norvegica population closer to the surface. When D. acuminata and D. norvegica co-occurred, their abundances peaked at different depths; this was observed even when both species formed maxima in the surface layer., authorCount :4

A naked dinoflagellate with a unique arrangement of chloroplasts in the center of the cell was isolated from the northern Baltic proper during a spring dinoflagellate bloom (March 2005). Morphological, ultrastructural, and molecular analyses revealed this dinoflagellate to be undescribed and belonging to the genus Gymnodinium F. Stein. Gymnodinium corollarium A. M. Sundström, Kremp et Daugbjerg sp. nov. possesses features typical of Gymnodinium sensu stricto, such as nuclear chambers and an apical groove running in a counterclockwise direction around the apex. Phylogenetic analyses based on partial nuclear-encoded LSU rDNA sequences place the species in close proximity to G. aureolum, but significant genetic distance, together with distinct morphological features, such as the position of chloroplasts, clearly justifies separation from this species. Temperature and salinity experiments revealed a preference of G. corollarium for low salinities and temperatures, confirming it to be a cold-water species well adapted to the brackish water conditions in the Baltic Sea. At nitrogen-deplete conditions, G. corollarium cultures produced small, slightly oval cysts resembling a previously unidentified cyst type commonly found in sediment trap samples collected from the northern and central open Baltic Sea. Based on LSU rDNA comparison, these cysts were assigned to G. corollarium. The cysts have been observed in many parts of the Baltic Sea, indicating the ecologic versatility of the species and its importance for the Baltic ecosystem.

Udgivelsesdato: August 2009, A naked dinoflagellate with a unique arrangement of chloroplasts in the center of the cell was isolated from the northern Baltic proper during a spring dinoflagellate bloom (March 2005). Morphological, ultrastructural, and molecular analyses revealed this dinoflagellate to be undescribed and belonging to the genus Gymnodinium F. Stein. Gymnodinium corollarium A. M. Sundström, Kremp et Daugbjerg sp. nov. possesses features typical of Gymnodinium sensu stricto, such as nuclear chambers and an apical groove running in a counterclockwise direction around the apex. Phylogenetic analyses based on partial nuclear-encoded LSU rDNA sequences place the species in close proximity to G. aureolum, but significant genetic distance, together with distinct morphological features, such as the position of chloroplasts, clearly justifies separation from this species. Temperature and salinity experiments revealed a preference of G. corollarium for low salinities and temperatures, confirming it to be a cold-water species well adapted to the brackish water conditions in the Baltic Sea. At nitrogen-deplete conditions, G. corollarium cultures produced small, slightly oval cysts resembling a previously unidentified cyst type commonly found in sediment trap samples collected from the northern and central open Baltic Sea. Based on LSU rDNA comparison, these cysts were assigned to G. corollarium. The cysts have been observed in many parts of the Baltic Sea, indicating the ecologic versatility of the species and its importance for the Baltic ecosystem.

Växtplanktonsamhällets sammansättning under sommaren har förändrats i alla havsområden under senare år. Exempelvis har filamentösa cyanobakterier ökat i Egentliga Östersjön. Den troligaste förklaringen är ändrade hydrografiska förutsättningar, så som ökad humustillförsel från land, försämrat ljusklimat, minskad salinitet och ökad temperatur orsakad av ändringar i klimatet.

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