DISTRIBUTION AND POPULATION-DYNAMICS OF OSTRACODES (CRUSTACEA, OSTRACODA) IN A KARSTIC LAKE - LAKE BANYOLES (CATALONIA, SPAIN)

Qualitative and quantitative benthic samples were collected monthly be tween December 1986 and December 1987 from several stations at various depths and basins in the karstic Lake Banyoles (Catalonia, Spain), to study the spatial distribution and seasonality of ostracodes. A total of eight ostracode species were found in the lake. Of these, Candona neglecta Sars, Isocypris beauchampi Paris and Cypria ophtalmica Jurine were the most common ostracodes at all depth stations. Darwinula stev ensoni Brady & Robertson, Ilyocypris species (I. bradyi Sars and I. gi bba (Ramdohr)), Cyprideis torosa (Jones) and Cyclocypris ovum Jurine, on the other hand, were confined to sublittoral and littoral areas of the lake. Substrate and organic matter content appeared to be relevant factors determining the distribution of ostracode species at the diff erent stations. The highest abundance of ostracodes were in the sublit toral (Basin IV-7 m and Basin I-5 m) where the substrate was coarse an d sediment had a high organic matter content (>35% LOI). Low oxygen le vels in the hypolimnetic waters (i.e. <1 mg 1(-1)) may explain the abs ence of ostracodes at deeper zones in stations where the anoxic period lasts more than four months. On the other hand, low temperatures seem to favour the development of C. neglecta and D. stevensoni, while wit h higher temperatures I. beauchampi, C. torosa and C. ovum increased t heir abundances. However, no clear pattern can be observed, so ostraco de species in Lake Banyoles, apparently, have non-seasonal life histor ies.