Press release 2012-09-17 at 12:00
Aranda and Muikku, the research vessels of the Finnish Environment Institute, have returned from their August expeditions. On these tours, they studied the eutrophication of the Gulf of Finland, the southern Archipelago Sea, the Bothnian Bay and the Baltic Proper, the oxygen situation on the sea floor and changes in zoobenthic communities. Aranda monitored zoobenthic communities on its tour of the Baltic Proper in June.
These journeys form part of the long-term research undertaken by the Marine Research Centre of the Finnish Environment Institute into changes in the condition of the Baltic Sea. They also contribute to the joint HELCOM monitoring being conducted by the Baltic Sea countries. As part of the Baltic Sea Challenge, the Cities of Helsinki and Turku examined the state of their coastal waters on tours made by Muikku.
The oxygen depletion area in the Baltic Sea’s main basin is as extensive as it was in summer 2011, whereas the situation has improved on deep sea floors in the Gulf of Finland compared to last year. The oxygen situation is good on outer archipelago sea floors, but remains poor in certain coastal water areas in the inner archipelago. The number of benthic animals is high on sea floors with oxygen, particularly in the southern Archipelago Sea, but also in the outer archipelago of the Gulf of Finland. No significant changes were seen in the amount of algae in the Gulf of Finland compared to last year. However, at most observation sites, the concentration of chlorophyll a describing the amount of algae was now lower than it was in the middle of last decade. The oxygen situation in the Bothnian Sea and the Bothnian Bay remains healthy.
Oxygen situation mainly poor and no benthic animals in the Baltic Proper
In recent years, the deep water and sea floor oxygen situation in the Baltic Sea’s main basin has been extremely poor in central and northern deep water areas in the Baltic Proper. Benthic fauna was completely absent from oxygen-depleted areas.
No significant changes in the condition of the Gulf of Finland compared to last year
The condition of the Gulf of Finland’s coastal waters has improved since 2006 in outer archipelago areas, but oxygen depletion is still found in places in deep water areas of the inner archipelago throughout the coastal area. Conditions in these areas have not improved. In deep water areas of the Gulf of Finland in particular, poorer oxygen conditions and higher nutrient concentrations are significantly influenced by the intermittent inflow of low-oxygen deep water from the Baltic Sea’s main basin into the Gulf of Finland, even into its eastern reaches. In shallow and highly eutrophic coastal waters, summertime temperature stratification affects oxygen depletion in the water layers close to the sea floor, reinforcing internal load and accelerating eutrophication.
At R/S Muikku’s observations sites, conditions in the bottom sediments and zoobenthic communities were similar to last year. At 37 per cent of all the 57 observation sites, the surface sediments were considered oxygen-free. Most sea floors in poor condition were located in the eastern and western reaches of the inner archipelago. On the expedition included in the City of Helsinki’s Baltic Sea Challenge, the condition of the coastal waters of Helsinki, Sipoo and Espoo was studied. At approximately 40 per cent of the 50 observation sites studied, the sea floor’s condition was found to be alarmingly poor.
In the Gulf of Finland, about one fifth of all observation sites were completely without benthic animals. However, in many places in the Gulf of Finland, zoobenthic communities still comprise only a few species. Typically, the only species observed in sea floors where the oxygen situation was reasonable or poor was an alien species, Marenzelleria viridis. Monoporeia affinis communities, indicating good sea floor conditions, were found at a considerably higher number of sites than five years ago. However, on the deepest sea floors, the oxygen situation was poor, with a very low number of benthic animals seen at these R/S Aranda observation sites.
Almost without exception, the oxygen situation was good in the southern reaches of the Archipelago Sea and their zoobenthic communities comprised many species. On the Baltic Sea Challenge expedition in the coastal area of Turku, zoobenthic communities were scarcer, but only one site was found to be completely without benthic animals and oxygen-free.
Both in the open sea areas and the coastal waters of the Gulf of Finland, algae amounts were similar to last year. A significant change compared to the situation in previous decades was that the chlorophyll values in the eastern reaches of the Gulf of Finland were no longer significantly higher than in other sea areas. Eutrophication, which accelerated until the middle of last decade, appears to have levelled off throughout the sea area, most notably in the east. The most important factor behind this development has been the decline in internal load.
Abundant oxygen on Bothnian Sea and Bothnian Bay sea floors
Since late 2010, saltier seawater has streamed in from the main basin of the Baltic Sea to the Bothnian Bay, via the Åland Sea and the Archipelago Sea, and it has mixed with the top water layers during 2012. Oxygen levels in the Bothnian Sea and the Bothnian Bay remain healthy.
The amount of blue-green algae in this area continues to be significantly lower than in the rest of the Baltic Sea. Blue-green algae were seen in abundant numbers in plant plankton in the Bothnian Sea’s open sea areas, while green algae were dominant in the Bothnian Bay.
The surface water temperatures and nutrient levels measured during the expedition, which were lower than the average for this time of year, support the national algal summary published by the Marine Research Centre on 13 September 2012: “Fewer blue-green algal blooms were observed throughout summer 2012 due to the coldness of waters and the windy weather.”
Medusae found in large numbers
This is the third consecutive year that observations of medusae or jellyfish are collected from citizens through an observation form available at the Baltic Sea Portal. In addition, observations have been made on Aranda’s expeditions.
This summer the moon jelly (Aurelia aurita) occurred in large numbers in the Gulf of Finland, the Archipelago Sea and the Åland Sea. In addition, observations were made in the Bothnian Sea. The Olkiluoto nuclear power plant has been informed of the dense medusa communities of the early autumn, as these can block up pipes. Dense communities have also been observed in other sea areas, especially in coastal areas, where medusae drift with the wind and the currents.
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Oxygen levels in the Baltic Sea in August 2011 and 2012
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More information:
Aranda:
Leader of the expedition Pekka Kotilainen
Finnish Environment Institute
firstname.lastname@ymparisto.fi
Tel. +358 400 1485 20
Leader of the expedition Maiju Lehtiniemi
Finnish Environment Institute
firstname.lastname@ymparisto.fi
Tel. +358 40 7255 085
Muikku:
Leader of the expedition Seppo Knuuttila
Finnish Environment Institute
firstname.lastname@ymparisto.fi
Tel. +358 40 7609 232
The Baltic Sea challenge
Jari-Pekka Pääkkönen
City of Helsinki
firstname.lastname@hel.fi
Tel. +35850 556 4283
Olli-Pekka Mäki
City of Turku
firstname.lastname@turku.fi
Tel. +35850 557 3138
Communication
Aira Saloniemi, SYKE Communications, Baltic Sea
firstname.lastname@ymparisto.fi
Tel. +358 400 1488 75