ZOOPLANKTON IN LOCH-LOMOND - PERSPECTIVES, PREDATION AND POWAN

Published and unpublished accounts of the zooplankton community of Loc h Lomond are reviewed. Loch Lomond's zooplankton community is unique a mongst those of Scotland's other large lochs. Holopedium gibberum appe ared in Loch Lomond in the years between the studies of Slack & Hamilt on in the 1950s and zooplankton surveys in the late 1970s. The annual cycles of Eudiaptomus gracilis, Cyclops strenuus abyssorum and Mesocyc lops leuckarti are described for the mid basin of Loch Lomond. E. grac ilis overwinter mainly as adults with variable egg production during t heir lifespan of 5-8 months. The cyclopoid copepods have variable life history characteristics. C. str. abyssorum produce a single generatio n per year, overwinter by means of resting eggs and a small population of planktonic adults, while M. leuckarti is present in the plankton t hroughout the year, but in low numbers during winter. Zooplankton popu lations in Loch Lomond are predated by the diverse fish community whic h includes a facultative planktivore in the powan, Coregonus lavaretus . Powan feed heavily on zooplankton from late spring until late autumn . Powan display selectivity in the prey species taken, in the size dis tribution and morph types taken within prey species. Zooplankton speci es, morphs and forms in Loch Lomond tend to reflect this predation.