The neuston of the subtropical and boreal North-eastern Atlantic Ocean. A review

The present paper compiles results of recent studies on distribution, abundance, migratory pattern and feeding of invertebrates and early stages of fish in the uppermost layer of the subtropical and boreal Atlantic Ocean. Three ecological groups are described: euneuston, living permanently at the surface; facultative neuston, invading the uppermost layer mainly during night; pseudoneuston, comprising the uppermost part of populations which are mainly concentrated in deeper layers. For several species of fish, a shift in behaviour was found: eggs and yolk-sac larvae are mainly missing from the uppermost layers, young post-larvae staying permanently close to the surface, and old larvae and juveniles performing diurnal vertical migrations. During daytime, the uppermost layer serves as a refuge for only a small number of welladapted organisms, while at dusk and at night considerable immigration occurs. During daytime, zooneuston is mainly carnivorous or omnivorous. In boreal and turbid waters, the ecological differences between the uppermost and lower layers are reduced. Neuston is an important element of the ecosystem in these areas.