State of the Gulf of Finland in 2003

3 INTRODUCTION 4 THE ICE SEASON 2003/2004 4 NUTRIENT LOADING 5 HYDROGRAPHY AND OXYGEN CONDITIONS 6 NUTRIENTS 7 MACROZOOBENTHOS 11 PHYTOPLANKTON 13 The vernal period 14 The late-summer period 14 INVASIVE SPECIES 17 FISHING 18 HARMFUL SUBSTANCES 19 Dioxins 19 Sediments 19 Fish 20 Heavy metals in Baltic herring 22 OIL POLLUTION 23 REFERENCES 25 STATE OF THE GULF OF FINLAND IN 2004 Hannu Haahti' & Pentti Kangas5 (Editors) Pekka Alenius', Alexander Antsulevich2, Svetlana Basova3, Nadezhda A. Berezina4, Heli Haapasaari5, Andreas Jaanus? , Kalervo Jolmas, Pirkko Kauppila5, Seppo Knuuttilaa, Markku Korhonen5, Jonne Kotta', Ari Laine', Mirja Leivuori', Urmas Lips6, Larissa F. Litvinchuk4, Alexey A. Maximov4, Alf Norkko', Marina I. Orlova4, Heikki Peltonen5, Jukka Pönni7, Mika Raateoja', Johanna Räsänen5, Simo Salo5, Jouni Vainio', Jenni Vepsäläinen5 & Matti Verta5 ' Finnish Institute of Marine Research (FIMR), P.O. Box 2, FI-00561 Helsinki, Finland 2 St. Petersbug State Univ., Depart. of Hydrobiology and Ichthyology, 16 line, 29, 199178, St. Petersburg, Russia 3 NW Administr. of Roshydromet (NW Roshydromet), 23rd line 2a, Vasily Island, 199026, St. Petersburg, Russia 4 Zoological Institute, Russian Academy of Sciences, University Embankment 1, 199034, St. Petersburg, Russia 5 Finnish Environment Institute (SYKE), P.O. Box 140, FI-00251 Helsinki, Finland 6 Estonian Marine Institute (EMI), 10a Mäealuse Street, Tallinn, 12618, Estonia Finnish Game and Fisheries Research Institute (FGFRI), P.O. Box 2, FI-00791, Helsinki, Finland ABSTRACT In the eastern part of the Gulf of Finland the freezing started in mid-December 2003 — approximately two weeks later than usual. In the western and the middle parts of the Gulf of Finland the freezing started at the turn of the year, the average time. In early March a period of cold weather set in and more new ice formed rapidly. The greatest ice cover of the Baltic Sea — 152 000 km2 — was reached on the 11th of March. When classified by the extent of the ice cover, the ice season 2003/04 of the Baltic Sea was average. In 2004 the salinity and density stratifications were normal for a part of the year. In the summer there was a clear halocline in the middle of the gulf at a depth of 60 m. Oxygen conditions were poor below the halocline in summer. In the autumn vertical mixing was rather strong, resulting in better oxygen conditions at greater depths. Salinity was rather high, as in 2003, at mid to bottom depths in the central gulf in comparison with the last 10 years. After some storm events in late December 2003, the water mass from Helsinki eastward was mixed throughout. Phosphate concentrations were, due to effective mixing, unusually high in the surface layer east of Helsinki and varied between 0.71 and 1.42 μcoo1/1 in the whole Gulf of Finland at the beginning of the year 2004. The state of sea bottoms in 2004 was mostly very poor. The monitoring stations of the open sea generally showed deep water oxygen values below 3 mg/1 and in the deep parts of the western Gulf hydrogen sulphide was measured from near-bottom samples. Oxygen concentrations of the local deeps along the archipelago waters of the northern coast were exceptionally low as well. The poor oxygen conditions were reflected as an almost total absence of zoobenthos both in the open Gulf and along the northern coast. In the shallow easternmost Gulf (Neva Estuary) oxygen conditions were relatively good and benthic fauna was also found there. The algal biomasses in late summer were clearly higher than the average during the latest decade. The algal community was dominated by mixed communities of the cyanophytes Nodularia spumigena, Anabaena sp. , and Aphanizomenon flos-aquae. The dinoflagellate Heterocapsa triquetra was also common. Although the cyanobacterial biomasses were moderately high as early as in late July, surface accumulations at their widest extent were observed only in early August due to the lack of sufficiently long calm periods.In the eastern part of the Gulf of Finland the freezing started in mid-December 2003 — approximately two weeks later than usual. In the western and the middle parts of the Gulf of Finland the freezing started at the turn of the year, the average time. In early March a period of cold weather set in and more new ice formed rapidly. The greatest ice cover of the Baltic Sea — 152 000 km2 — was reached on the 11th of March. When classified by the extent of the ice cover, the ice season 2003/04 of the Baltic Sea was average. In 2004 the salinity and density stratifications were normal for a part of the year. In the summer there was a clear halocline in the middle of the gulf at a depth of 60 m. Oxygen conditions were poor below the halocline in summer. In the autumn vertical mixing was rather strong, resulting in better oxygen conditions at greater depths. Salinity was rather high, as in 2003, at mid to bottom depths in the central gulf in comparison with the last 10 years. After some storm events in late December 2003, the water mass from Helsinki eastward was mixed throughout. Phosphate concentrations were, due to effective mixing, unusually high in the surface layer east of Helsinki and varied between 0.71 and 1.42 μcoo1/1 in the whole Gulf of Finland at the beginning of the year 2004. The state of sea bottoms in 2004 was mostly very poor. The monitoring stations of the open sea generally showed deep water oxygen values below 3 mg/1 and in the deep parts of the western Gulf hydrogen sulphide was measured from near-bottom samples. Oxygen concentrations of the local deeps along the archipelago waters of the northern coast were exceptionally low as well. The poor oxygen conditions were reflected as an almost total absence of zoobenthos both in the open Gulf and along the northern coast. In the shallow easternmost Gulf (Neva Estuary) oxygen conditions were relatively good and benthic fauna was also found there. The algal biomasses in late summer were clearly higher than the average during the latest decade. The algal community was dominated by mixed communities of the cyanophytes Nodularia spumigena, Anabaena sp. , and Aphanizomenon flos-aquae. The dinoflagellate Heterocapsa triquetra was also common. Although the cyanobacterial biomasses were moderately high as early as in late July, surface accumulations at their widest extent were observed only in early August due to the lack of sufficiently long calm periods. 4 Hannu Haahti & Pentti Kangas (Editors) MERI No. 55, 2006 Herring and sprat are the most abundant species in the Gulf of Finland and they constitute the majority of catches. Herring catches were 30 000-50 000 tons during 1980-2002. However, the catches collapsed in 2003 to c. 10 000 tons and further down to c. 7000 tons in 2004. This collapse was not due to decrease in fishing e.g. because of fisheries management or market factors, but merely due to decrease in fish abundance within the Gulf of Finland. The number of detected oil spills continued decreasing in 2004 and the number of oil spill detections was smaller than ever, even though the number of flight hours increased and Finland has intensified surveillance by utilising satellites in oil spill detection. Most of the detected oil spills are located along the shipping routes outside costal states' territorial waters.