Poor oxygen situation threatens Gulf of Finland - once again

A poor oxygen situation is once again threatening the Gulf of Finland.
      The Finnish research vessel Aranda noticed during its observation cruise earlier this week that salty water rich in nutrients has flowed from the Baltic Sea into the Gulf of Finland. This has caused the gulf’s water to stratify.
      Because the water fails to mix, the water layers near the bottom will gradually run out of oxygen.
      “The oxygen depletion situation at the western end of the Gulf of Finland is already pretty bad. During the course of the summer we are likely to have deeps void of any oxygen”, says Aranda tour leader Hannu Haahti from the Finnish Environment Institute SYKE.
      As late as in January, during the Aranda’s previous voyage, the water in the Gulf of Finland was still completely mixed.
      Haahti believes that the rapid stratification has been caused by the winds brought in by low pressure systems and the fluctuation of surface levels, which has formed currents.
     
The salty water has brought with it comb jellies or ctenophora further and further into the eastern parts of the Gulf of Finland. Now they were discovered for the first time even in front of the island of Haapasaari in Kotka.
      In all, fewer comb jellies were found than in January, however.
      So far it is not known whether the specimens gathered are Arctic comb jellies (Mertensia ovum) or the feared American comb jellies (Mnemiopsis leidyi), which are believed to present a threat to the Gulf’s fish populations (see linked article). Genetic testing will in time reveal the species of the samples collected.
     
Aranda also brought live comb jellies ashore. Researchers will try to breed them for the first time in a SYKE laboratory in Helsinki. The scientists are keen on studying the feeding and reproduction of the species.
      The comb jellies will be kept in fish tanks where water is circulated along the sides, keeping the jellies in motion and preventing them from sinking to the bottom. The water temperature will be set at four to five degrees, just like in the sea.
     
This was already the third time this year that the Aranda screened the Gulf of Finland.
      The aim of the intensified monitoring is to map out the Gulf of Finland’s nutrition, oxygen, and salt content situation, and to find out what kind of effects the implemented environmental efforts, such as the introduction of the St. Petersburg waste water treatment facilities, have had on the troubled and threatened body of water.


Previously in HS International Edition:
  Gulf of Finland has slightly higher oxygen level than last summer (14.8.2007)
  Finnish-Russian study finds high cadmium levels in eastern Gulf of Finland (13.3.2008)
  Baltic Sea needs urgent attention (14.4.2008)
  St. Petersburg reduces phosphorous emissions into Gulf of Finland (2.10.2007)

See also:
  Feared comb jellies found in Baltic turn out to be harmless species (10.2.2009)

Links:
  Finnish Environment Portal
  Finnish Environment Institute SYKE: Marine Research
  R/V Aranda on the Baltic Sea Portal
  Ctenophore (Wikipedia)
  The Baltic Sea Portal: Arctic Comb Jelly