The Zooplankton Of The Baltic Proper: A long-term investigation of the fauna, its biology and ecology

This paper is based on the results from a long-term zooplankton investigation in the Baltic proper in the years 1968—1972. Additional results, obtained by the authors in more recent investigations, have also been used in order to enrich the material with information not obtained in the principal investigation. Seven standard plankton stations, covering seven sub-areas of the Baltic proper have been visited on average four to five times per year. All cruises have been made in connection with ordinary hydrographical expeditions which means that all zooplankton samples are accompanied by a complete list of hydrographical data. The paper describes the zooplankton fauna of the Baltic proper which comprises about 40 regularly appearing species excluding the micro zooplankton. The main part of the fauna in respect of biomass and production consists, however, of only 10—12 species. The most important were the cnidarian Aurelia aurita. the rotifers Synchaeta spp., the cladocerans Bosmina coregoni maritima and Evadne nordmanni, the copepods Pseudocalanus minutas elongatus, Temora longicornis, Acartia bifilosa, A. longiremis and Centropages hamatus and the larvacean Fritillariaborealis. Species of less importance were the larvae of Pleurobrachia pileus, the cladocerans Podon intermedius, P. leuckarti and Pleopsis polyphemodides (the latter is abundant in coastal areas), the copepods Eurytemora sp. and Oithona similis, the larvae of gastropod species, Mytilus edulis, Macoma baltica, Cardium glaucum. C.hauniense and My a arenaria, the chaetognath Sagitta elegans baltica and the larvacean Oikopleura dioica. Occaisonal species were the cnidarians Sarsia tubulosa and Cyanea capillata, the rotifers Keratella quadrata quadrata, K. qu. platei, K. cruciformis eichwaldi and K.cochlearis recurvispina, the larvae of Pygospio elegans and Balanus improvisus, the copepods Calanus finmarchicus, Limnocalanus macrurus and Cyclops sp., the mysidaceans Mysis relicta and M. mixta, the amphipod Hyperia galba and the chaetognath Sagitta setosa. All samples have been collected by vertical, fractionated hauls with a Nansennet. The mesh size was 0.160 mm in the years 1968—1971 and 0.090 mm in 1972. A correction of all results due to the poor filtering capacity of the Nansen net has been made. The additional results are mainly based on samples from the UNESCOWP 2 net. All specimens have been analysed to species and the copepods also to developmental stages. The biomass has been calculated as t