EFFECT OF ZOOPLANKTON TYPE AND ABUNDANCE ON PREY CONSUMPTION BY THE FAIRY SHRIMP, STREPTOCEPHALUS-PROBOSCIDEUS (ANOSTRACA, CRUSTACEA)

Laboratory cultured Streptocephalus proboscideus (three sizes (mm), vi z. 8.44 +/- 0.95 (virgin), 14.18 +/- 1.49 (adult I) and 19.24 +/- 1.52 (adult II)) were offered (separately for males and females) field col lected zooplankton (12 prey types) at three levels of abundance (1.0 m l(-1), 2.0 ml(-1) and 4.1 ind. ml(-1)) in 30-minute feeding experiment s. Gut contents, analyzed for abundance and diversity of prey type, sh owed that predator size, sex and their interaction had strong effects on prey consumption. Regardless of their size, and of prey density, S. proboscideus females consumed 25-90% more prey than males. Their filt ration rates (adult II) were higher (125 mi ind.(-1) h.(-1)) than thos e of males (30 mi ind.(-1) h.(-1)) too. Rotifers had the highest numer ical Percentage in the gut, regardless of predator size or sex. Cladoc erans were only consumed by adults I and II. Adult II females consumed 28.5-43.3 mu g zooplankton dry weight ind.(-1) h.(-1). Size distribut ion of B. longirostris in the field and in the,out were closely simila r. This study confirms S. proboscideus as a non-selective filter feede r. Since it did not eat jumping rotifers, copepod nauplii and copepodi tes, it may contribute to structuring its prey communities, because go od escapers will be enriched in the medium, while poor escapers will b e depleted.