ZOOPLANKTON IN ANCIENT AND OLIGOTROPHIC LAKE OHRID (EUROPE) IN ASSOCIATION WITH ENVIRONMENTAL VARIABLES

Analiziran je sastav zooplanktona u geološki starom, tektonskom Ohridskom jezeru (Makedonija, jugoistočna Europa). Glavni cilj rada bio je utvrditi sezonske i prostorne značajke funkcionalnih hranidbenih skupina zooplanktona i njihovu povezanost s uvjetima okoliša. Najveća produkcija zooplanktona utvrđena je u metalimniju, u kojem su biomasa fitoplanktona i brojnost zooplanktona postigle najveće vrijednosti. Utvrđeno je 16 pelagičkih vrsta od kojih dvije endemične: Arctodiaptomus steindachneri (Richard, 1897) i Cyclops ochridanus (Kiefer, 1932). Zooplankton pelagijala bio je zastupljen s niskom brojnošću, 25 ± 22 ind. L-1, a najveći udio, 60 %, postigli su veslonošci. Unutar trofičke skupine mikrofaga, prevladavali su tijekom ljeta kolnjaci s vrstom Kellicottica longispina (Kellicott, 1879), a naupliji veslonožaca prevladavali su u proljeće Eudiaptomus gracilis (Sars, 1862) and C. achridanus i jesen C.achridanus. Ova trofička skupina hrani se suspenzijom bakterija i detritusa, te je tijekom istraživanog razdoblja zauzimala afotički hipolimnij. Predatori su uglavnom bili zastupljeni s kopepoditima i odraslim veslonošcima u metalimniju. Na njihove populacije su značajno i pozitivno utjecali: temperatura (r = 0.417, p = 0.001), otopljeni kisik (r = 0.463, p = 0.0001) te najizraženije biomasa fitoplanktona (r = 0.708, p < 0.00001). Ovo istraživanje među prvima razmatra zooplankton Ohridskog jezera kao važnu kariku unutar hranidbene mreže ovog oligotrofnog ekosustava.Zooplankton is studied in the ancient, tectonic, oligomictic and oligotrophic Lake Ohrid (Macedonia, South Eastern Europe). The main aim of this study was to assess the seasonal and spatial patterns of the zooplankton functional feeding guilds in relation to the environmental conditions. Metalimnion of the lake was detected as the most productive environment, where biomass of the phytoplankton and abundance of the zooplankton reached their maxima. Pelagial zooplankton of low abundance (25 ± 22 ind. L-1) consisted of 16 species including two endemic copepods, Arctodiaptomus steindachneri (Richard, 1897) and Cyclops ochridanus (Kiefer, 1932). Copepods obtained remarkable share (60%) in the zooplankton assemblage. Microphagous zooplankton was mainly comprised of the most abundant rotifer Kellicottia longispina (Kellicott, 1879) in summer, and copepod nauplii during the spring Eudiaptomus gracilis (Sars, 1862) and C.ochridanus, and autumn C.ochridanus. Due to their requirements for the bacterio-detritus suspension, this microphagous zooplankton occupied aphotic hypolimnion during the entire study period. Raptorials were typically represented by copepodites and adult copepods in the metalimnion, and were significantly and positively affected by temperature (r = 0.417, p = 0.001), dissolved oxygen (r = 0.463, p = 0.0001) and, particularly, phytoplankton biomass (r = 0.708, p < 0.00001). This is the first study in which the link between the lower and higher trophic levels is investigated in Lake Ohrid