Diatoms have increaed and filamentous blue-green algae have further decreased both in the Finnish open-sea areas and the Baltic Proper. Though the amount of phosphate-phosphorus has increased in the Gulf of Finland, the general nutrient level is still low in the Baltic.
Vivi Fleming-Lehtinen and Seija Hällfors
General: The Chlorophyll a concentration is between 3 and 5 µg/l in the open Gulf of Finland and between 2 and 4 µg/l in the Baltic Proper, The surface temperature has decreased, and is between 13 and 15 degrees in the Gulf of Finland and between 14 and 15 degrees in the Baltic Proper.
The wave buoy in the Northern Baltic. Photo Mikko Rauhala.
Nutrients: The sum of nitrate- and nitrite-nitrogen concentration is in the Gulf of Finland and the Northern Baltic Proper below 1 µmol/l. The phosphate-phosphorus concentration has increased in the Gulf of Finalnd during the previous weeks, and is now 0.2 µmo/l. In the Baltic Proper the concentration is from 0.5 to 1 µmol/l. The silicate-silicon concentration is from 8 to 10 µmol/l in the Gulf of Finland and from 8 to 11 µmol/l in the Baltic Proper.
Species composition: has turned to autumnal. Blue-green algae are rapidly disappearing , only the filamentous blue-green alga Aphanizomenon flos-aquae occurs sparsely in all samples, Anabaena* spp. and Nodularia spumigena* are very scarse. Small colonial blue-green algae (Woronichinia spp., Snowella spp., Aphanothece spp., Lemmermanniella spp., Cyanodictyon spp.) are moderately common only in the Gulf of Finland and northern Baltic Proper. Large dinoflagellates (Dinophysis* spp.) are very sparse, except Heterocapsa triquetra that occurs in moderate amounts in the western Gulf of Finland. The diatoms Coscinodiscus granii and Actinocyclus octonarius have inceased in numbers, especially in the central Gulf of Finland, Skeletonema costatum is more common and Dactyliosolen fragillissimus is still very abundant in the Arkona Basin. Cryptophytes (Teleaulax spp., Plagioselmis prolonga), prasinophytes (Pyramimonas spp.) and the euglenophyte Eutreptiella gymnastica dominate the nanoplankton fraction, while haptophytes (Chrysochromulina* spp.) are relatively common only in the southern Baltic Sea. (*toxic or harmful species)
