Phytoplankton biomass and species succession in the Gulf of Finland, Northern Baltic Proper and Southern Baltic Sea in 2009

Transcription

1 Phytoplankton biomass and species succession in the Gulf of Finland, Northern Baltic Proper and Southern Baltic Sea in 2009 Authors: Seppo Kaitala and Seija Hällfors, Centre for Marine Research, Finnish Environment Institute Key message The spring bloom was larger than long term average in the Northern Baltic Proper, otherwise the chlorophyll-a levels followed close to the long term average. Results and assessment

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3 Fig. 1. Annual variation of chlorophyll a (mg m-3) in the western Gulf of Finland (upper), the northern Baltic Proper (middle), and the Southern Baltic Proper (lower). The blue curve represents the average for the years , the black diamonds the measurements made in Image: SYKE/Alg@line. Fig. 2. The relative cyanobacterial bloom index calculated from visual observations for 2009 and for in coastal and open sea areas surrounding Finland. Data from the Finnish Regional Environmental Centres, SYKE and FIMR. For description of method see or contact SYKE. Relevance of the indicator for describing developments in the environment Eutrophication is considered one of the most serious threats against the Baltic Sea. It is defined as an increase in the rate of supply of organic matter to an ecosystem, and is most commonly caused by nutrient enrichment. Chlorophyll a concentration, representing phytoplankton biomass, assesses the eutrophication-driven alterations of the Baltic Sea. More importantly, it can address with an adequate precision the intensity and occurrence of cyanobacterial blooms. It must be kept in mind, however, that although highly responsive to changes in surface nutrient concentrations, chlorophyll a is also a product of parameters not related to eutrophication, namely other biological factors, hydrography and climate. Policy relevance and policy references Although being a natural phenomenon per se, the algal bloom events have become more frequent, intense, and extensive due to the eutrophication of the Baltic Sea. Since the mid-90 s, the strength of cyanobacterial blooms have increased to levels to raise wide public concern. Currently, noxious and often harmful cyanobacterial blooms disrupt the functioning of the Baltic ecosystem, limit the recreational and economic use of the sea, and represent a clear and present health risk for humans and domestic animals. No signs of decrease of cyanobacterial blooms have been seen yet. Assessment for the Gulf of Finland 2009 The spring bloom started in early April, and reached its peak in late April as in the previous year. The diatoms Thalassiosira levanderi and Skeletonema costatum coll. dominated the beginning of the bloom while T. baltica, Chaetoceros ceratosporus, C. holsaticus, C. wighamii and Achnanthes taeniata became

4 more common during the peak. The dinoflagellates Biecheleria baltica, Scrippsiella hangoei and Peridiniella catenata became dominant during the peak. Small dinoflagellates Gymnodiniales spp. and the colonial chrysophyte Dinobryon balticum became dominant in May, while the haptophycean Chrysochromulina* spp., the green alga Monoraphidium contortum and the dictyochophycean Pseudopedinella tricostata were the most abundant taxa in June. The filamentous blue-green algae Aphanizomenon flos-aquae and Anabaena spp. increased with the increasing water temperature and became dominant in the beginning of July, when also the dinoflagellate Dinophysis acuminata was moderately abundant. Due to windiness and cool waters the surface accumulations of bluegreen algae did not grow large and were short of duration. For most of the time they were mixed in the water column. The toxic species Nodularia spumigena * became more abundant in August and also the dinoflagellate Heterocapsa triquetra was common in the western parts of the gulf. At the beginning of August cyanobacterial surface blooms began to occur in the open sea areas, but the variable weather dispersed the surface accumulations and re-formed them after a calm period. Occasional mass occurences of Aphanizomenon flos-aquae were observed until late November in the coastal areas. Small flagellates, mainly cryptophytes, dominated during the autumn. No late diatom bloom was observed. Assessment for the Northern Baltic Proper 2009 The spring bloom started in early April and reached its peak in late April. The chlorophyll a peak value was ca double compared to the weakly average between 1992 and No unusual nutrient values were observed. The species dominating the bloom was a newly described dinoflagellate Gymnodinium corollarium of the species complex Biecheleria baltica/scrippsiella hangoei/gymnodinium corollarium and also Peridiniella catenata. Later in May nanoflagellates became abundant and the dominating taxa were the prasinophycean Pyramimonas spp., dinoflagellates Gymnodiniales spp. and Heterocapsa rotundata and the colonial chrysophyte Dinobryon balticum. Larger dinoflagellates, particularly Dinophysis norvegica and Protoperidinium spp., were moderately common in the end of May. The haptophytes Chrysochromulina spp. became dominant in June, when also the blue-green algae Aphanizomenon flos-aquae and Anabaena spp. at first, later also Nodularia spumigena started to increase in mid June. Surface accumulations of bluegreen algae covered large parts of the Baltic Proper in mid July. In mid August the amount of Nodularia spumigena, and Anabaena spp. decreased, while Aphanizomenon flos-aquae still remained common. Narrow oscillatorealean filaments (Pseudanabaena sp.), small colonial blue-green algae (Aphanothece spp., Cyanodictyon spp., Woronichinia spp.) and and nanoflagellates (Chrysochromulina spp., the cryptophycean Plagioselmis prolonga and Teleaulax spp. and the prasinophycean Pyramimonas spp.) were the most abundant taxa in August. The diatoms Cyclotella choctawhatcheeana and Chaetoceros danicus and C. impressus were moderately common in September, but not in bloom concentrations. The invasive dinoflagellate Prorocentrum minimum occurred but sparsely during September-November. Most of the Chrysochromulina spp. cells disappeared during October and the cryptophytes Teleaulax spp. and Plagioselmis prolonga became dominant. The diatoms Coscinodiscus granii, Actinocyclus octonarius, Chaetoceros danicus, C. subtilis, C. impressus and Skeletonema costatum coll. and a few larger dinoflagellates Dinophysis acuminata, D. norvegica and D. rotundata, Protoperidinium brevipes and P. pellucidum occurred in small cell numbers.

5 Assessment for the Southern Baltic Proper 2009 The diatoms Skeletonema costatum coll., Chaetoceros spp. and Thalassiosira spp., cryptophytes, and the haptophyte Chrysochromulina polylepis occurred in low cell numbers in February and early March. They became common in mid March and very abundant in the beginning of April. The diatom Diatoma tenuis codominated with Chrysochromulina polylepis in late April. The spring dinoflagellate Peridiniella catenata was observed only in minor amounts. Small colonial blue-green algae and nanoflagellates (Chrysochromulina ssp., small gymnodinoids, Pyramimonas spp.) dominated in May. Blue-green algae, particulary small colonial species (Cyanodictyon spp., Aphanothece spp.), became dominant towards the end of June. The filamentous green alga Planctonema lauterbornii was exceptionally abundant in the beginning of July, usually it occurs sparsely during all the growing season. The filamentous species (Aphanizomenon flos-aquae, Anabaena spp., Nodularia spumigena,) and the chrooccalealean species were common in July. Most of the filamentous blue-green algae disappeared in the beginning of August, and nanoflagellates and colonial blue-green algae were again the dominant taxa. Diatoms (Chaetoceros impressus, C. danicus, Attheya longicornis and Nitzschia paleacea) became common, but the invasive alien dinoflagellate Prorocentrum minimum remained rare. Diatoms (Coscinodiscus granii, Actinocyclus octonarius, Chaetoceros spp., Skeletonema costatum) dominated also in October-November. References Fleming, V. & Kaitala, S Phytoplankton spring bloom biomass in the Gulf of Finland, Northern Baltic Proper and Arkona Basin in Helcom Indicator Fact Sheet. Hajdu,S., Hällfors, S., Gromisz, S., Skejvik, A.-T., Busch, S., Kownacka, J., Jurgensone, I., Olenina, I., Huseby, S., Andersson, A:, Wasmund, N., Jaanus, A., Hällfors, G., Rintala, J.-M., Majaneva, M., Blomster, J., Unusual phytoplankton event during winter-spring HELCOM Indicator Fact Sheets Online: Metadata Technical information 1. Data provider (source): Finnish Environment Institute SYKE. Contact persons: Seppo Kaitala and Seija Hällfors. 2. Description of data: Original unit of measure: mg chl a m-3. Semiquantitative phytoplankton analyses are based on the ranks 1 to 5 describing relative sample-based abundance of an algal species. In the cyanobacterial bloom map, visual observations are included. Original data in WGS84-coordinates Original purpose of the data: Phytoplankton monitoring the Baltic Sea, SYKE, Alg@line project 3. Geographical coverage: Gulf of Finland, Northern Baltic Proper, Southern Baltic Proper 4. Temporal coverage:

6 5. Methodology and frequency of data collection: The data has been collected using an automated flowthrough sampling system on merchant ships, sampling depth ca. 5 m, weekly sampling during the period February/March-October/November in each year. Detection device Jasco 750 spectrofluorometer 6. Methodology of data manipulation: No data manipulation Quality information 1. Strength and weakness (at data level) Strength: Very high both temporal and spatial sampling frequency Weakness: Satellite images are achieved only on clear weather. Ship-of-opportunity measurements are restricted to the ships route, and dependant on it's schedule; diurnal changes of data are not taken into account. 2. Reliability, accuracy, precision, robustness (at data level): Filtration and extraction of Chlorophyll a from samples according to accredited method SFS-EN ISO/IEC Procedure uncertainty: 5%. 3. Further work required (for data level and indicator level): More sophisticated statistical analysis For reference purposes, please cite this Baltic Sea environment fact sheet as follows: [Author's name(s)], [Year]. [Baltic Sea environment fact sheet title]. HELCOM Baltic Sea Environment Fact Sheets. Online. [Date Viewed],