In situ studies on the diurnal activity pattern of Diastylis rathkei (Cumacea, Crustacea) and its importance for the "hyperbenthos"

Abstract

1. Diastylis rathkeiKröyer exhibits negative phototaxis during the whole day. It never leaves the sediment as long there is any light. 2. The vertical migrations into the pelagic environment, as observed in August and October, start about one hour after sunset; they have their maximum intensity from about 22.00 h to 23.00 h and end at midnight. Diastylis rathkei reacts positively to light during this time. 3. Fishes and other predatory animals are almost inactive during this period. Population loss by predation is thus negligible or even lacking. 4. The literature on the "hyperbenthos" is critically discussed in relation to the method mostly employed, the use of Beyer's epibenthic closing net. This gear is not considered to be useful, and the results obtained by it are doubted. 5. Diastylis rathkei has no significance at all for the "hyperbenthos". The existence of this community in the Western Baltic Sea is doubted. © 1976 Biologischen Anstalt Helgoland.