Publication Date:
2022-08-05
Description:
In the subtropical NE Atlantic 337 neuston samples had been collected simultaneously in the 0-10 cm surface layer and in the adjacent 10-25 or 38-53 cm strata with a modified DAVID neuston catamaran. At a permanent station additional vertical stepwise hauls had been made down to 200 m with a Helgoland Larvae Net with a changing bucket device. Invertebrate neuston and other plankton was analysed in order to taclde the following problems: horizontal and vertical micro- and macrostratification, diurnal vertical migration, abundance, and feeding of species and their ontogenetical stages. Three ecological groups are described: 1. euneuston, living permanently in the uppermost layer (0-10 cm) by day and night; 2. facultative neuston, migrating into the surface layer mainly at crepuscular time and at night, or during certain phases of its early life history; 3. pseudoneuston, inhabiting with its highest concentration deeper layers, and reaching the immediate surface by relatively few specimens. - Contrary to the Black and Caspian Seas, the surface layer of the subtropical NE Atlantic is poor in nutrition compared with deeper layers. In the surface layer the total amount of invertebrates was only half of that in the adjacent strata of 10-25 and 38-53 cm, whereas the average concentration of Zooplankton in the 0-30 m macrolayer was eight times higher than in the surface layer. During daytime, particularly at noon, the average number of the invertebrate neuston diminished to 25 specimens/100 m3, and macrophages, i.e. mainly carnivores, represented about 75% of all the specimens, giving evidence of extreme scarcity of food at the sea surface. - The existence of a neuston biocoenoses in the subtropical NE Atlantic is discussed. The increase of the total number of invertebrates in the surface layer during dim light and at night, caused by facultative and pseudoneuston species, has to be regarded as an exchange of food between two communities: the biocoenoses of euneuston und pleuston on one hand and that faunal association on the other hand which is living in other habitats than at the very surface. Because of biological reasons and of terminological considerations the uppermost 5 to 10 cm thick layer at the sea surface should be called "pleustal".
Type:
Article
,
PeerReviewed
Format:
text
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