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Marine Ecology Progress Series

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MEPS 491:111-124 (2013)  -  DOI:

Distribution and reproduction of the Arctic ctenophore Mertensia ovum in the Baltic Sea

Maiju Lehtiniemi1,*, Elena Gorokhova2, Sören Bolte3, Holger Haslob4, Bastian Huwer5, Tarja Katajisto1, Lennart Lennuk6, Sanna Majaneva1, Arno Põllumäe6, Matthias Schaber4, Outi Setälä1, Thorsten B. H. Reusch3, Satu Viitasalo-Frösén1, Ilppo Vuorinen7, Pentti Välipakka8

1Finnish Environment Institute, Marine Research Center, PO Box 140, 00251 Helsinki, Finland
2Department of Applied Environmental Science & Department of Systems Ecology, Stockholm University, 10691 Stockholm, Sweden
3Helmholtz-Centre for Ocean Research (GEOMAR), Evolutionary Ecology of Marine Fishes, Düsternbrooker Weg 20,
24105 Kiel, Germany
4Johann Heinrich von Thünen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries, Institute of Sea Fisheries, Palmaille 9, 22767 Hamburg, Germany
5Technical University of Denmark, National Institute of Aquatic Resources, Charlottenlund Castle, Jægersborg Allé 1,
2920 Charlottenlund, Denmark
6Estonian Marine Institute, University of Tartu, Mäealuse 14, 12618 Tallinn, Estonia
7Archipelago Research Institute, University of Turku, 20014 Turku, Finland
8Centre for Economic Development, Transport and the Environment for Southeast Finland, PO Box 1041, 45101 Kouvola, Finland

ABSTRACT: Species identification based on morphological characteristics has caused misidentifications and led to twisted views of abundances and roles of ctenophores. Based on extensive field studies from 2007 to 2010, the occurrence of the arctic ctenophore Mertensia ovum was genetically verified in the southern, central and northern Baltic Sea, and its egg production, distribution and abundance were studied in relation to physical factors. Genetic analyses indicate that M. ovum is by far the most abundant small ctenophore in the Baltic Sea. Specimens from a 20 yr old ctenophore collection were also genetically identified as M. ovum, contrary to their previous morphological identification as another ctenophore species, Pleurobrachia pileus. Thus, earlier reports on P. pileus in the Baltic Sea may actually refer to M. ovum. The abundance of M. ovum was regulated by both salinity and temperature, with highest abundances found in sea areas and water layers at temperatures <7°C, salinities >5.5 and oxygen levels >4 ml l-1. During summer, the highest abundances of ctenophores and their eggs were found near the halocline, while the distribution was more uniform throughout the water column during winter. Only ctenophores >3.5 mm (oral-aboral length) produced eggs in the experiments, with an average rate of 2.2 eggs ind.-1 d-1. Finally, comparison with published data from the 1980s (assuming that those data refer to M. ovum) indicates that the present-day ctenophore abundance is ~80% lower in the north and ~55% higher in the southern parts of the Baltic Sea, due to reasons yet to be established.

KEY WORDS: Mertensia ovum · Pleurobrachia pileus · Identification · Abiotic factors · Egg production

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Cite this article as: Lehtiniemi M, Gorokhova E, Bolte S, Haslob H and others (2013) Distribution and reproduction of the Arctic ctenophore Mertensia ovum in the Baltic Sea. Mar Ecol Prog Ser 491:111-124.

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