Ecology of the Cladocera of the North Atlantic and the North Sea 1960-1967
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579; e-ISSN 1873-1406, more
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| Abstract |
The distributions, and seasonal and annual variations in abundance, of 5 spp of Cladocera are described and analysed. The material was collected by continuous plankton recorders from 1960-1967 inclusive at a standard depth of 10 m in the North Atlantic and the North Sea. Evadne nordmanni and Podon intermedius were neritic and oceanic, Podon leuckarti appeared to be typically neritic, Evadne spinifera typically oceanic, and 'Podon' polyphemoides indicative of estuarine waters. Spp are never abundant as long as the water column is not stratified. This phytoplankton-like dependence on stratification suggests that Cladocera need near-surface conditions for their successful propagation, both in neritic and in oceanic regions. It is shown that Cladocera are dispersed very effectively, so that almost as soon as environmental conditions have become suitable, whether in the open ocean or in coastal waters, animals will appear and populations become established. Evadne nordmanni and E. spinifera seemed to be mutually exclusive in all areas, as were Podon leuckarti and P. intermedius. Congeners have different temp tolerances and different temp optima. Podon leuckarti and Evadne nordmanni are cool-water spp, most abundant in spring and early summer; the larger Podon intermedius and Evadne spinifera are warm-water spp. The abundance of spp with a similar pattern of seasonal variation in abundance in any given area is influenced by the same combination of environmental factors. The patterns of annual fluctuation in abundance in different areas are increasingly less similar as the geographic distance increases between the areas that are compared. There seems to be no tendency to speculate. |
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