Feared comb jellies found in Baltic turn out to be harmless species

The dreaded comb jellies (Mnemiopsis ledyi) that were found in samples taken in the Baltic Sea last autumn appear to be a more benign Arctic variety of animal plankton, of the Mertensia family, native to arctic waters.
     The Mertensia is similar in many ways to the Mnemiopsis ledyi, but it is not believed to pose the same hazards to sea life.
     The Mertensia can grow to between 6 and 8 cm. while the Mnemiopsis ledyi, native to coastal waters of North and South America, can reach 15 cm. in length.
     
The closest habitats of the Mertensia are in waters off Iceland and Spitzbergen. It is not known to have caused the widespread destruction to fish stocks, like the Mnemiopsis ledyi has, when introduced to areas outside its own distribution, said special researcher Maiju Lehtiniemi on the marine research vessel, the Aranda in Helsinki on Monday. The ship had just returned from a research voyage.
     The Mnemiopsis ledyi has been blamed for extensive destruction of fish stocks in the Black Sea, after being introduced there, presumably in ships’ bilge water.
     
Comb jellies now believed to be of the Mertensia variety were found in samples taken in many parts of the Baltic. Precise identification might take some time.
     Lehtiniemi says that the Mertensia might actually occur naturally in the Baltic Sea.
     Researchers now say that the intrusive Mnemiopsis ledyi,which was first detected in samples taken in the Baltic in 2007 either did not survive the winter after all, or may have been misidentified to begin with.
     
The feared Mnemiopsis ledyi made headlines as the Finnish Institute of Marine Research was being split up and the parts merged with other institutes.
     When the independent Institute of Marine Research disappeared, Mnemiopsis ledyi appears to have disappeared as well.
      Eeva-Liisa Poutanen, former director-general of the institute insists, however, that these two things had nothing to do with each other. “Science is science, and political decisions are a different matter.”
     Poutanen, who now works as an official at the Ministry of the Environment, says that when the first Mnemiopsis ledyi were found, researchers were convinced that they had been correctly identified.


Previously in HS International Edition:
  Comb jellies still inhabit Gulf of Finland (22.9.2008)
  Research vessel Aranda to chart distribution of comb jellies in Baltic Sea (5.8.2008)
  Comb jellies threaten fish stocks off Helsinki (21.4.2008)
  Initiative for new sea centre to support marine research (14.1.2008)
  Invasive comb jellies now found throughout Baltic Sea (17.12.2007)
  Comb jelly poses serious threat to Baltic Sea ecosystem (27.8.2007)

Links:
  Global invasive species database: Mnemiopsis ledyi (comb jelly)