THE HORIZONTAL DISTRIBUTION OF PLANKTON IN A DEEP, OLIGOTROPHIC LAKE - LOCH-NESS, SCOTLAND

1. The horizontal distribution of plankton in Loch Ness, a deep, oligo trophic lake with a simple trench morphometry, was studied on three oc casions in 1993. Samples were collected from ten stations spaced along the length of the loch and the abundance of algae, bacteria, protozoa , rotifers and crustacean zooplankton was determined. 2. Horizontal va riability was found to be greatest for the metazoan zooplankton and fo r the algae, especially lure cryptomonad flagellates. Bacteria and het erotrophic protozoa showed relatively little horizontal variability. T he degree of horizontal variability was not sufficient seriously to af fect studies of the seasonality of plankton abundance conducted from a single sampling station. 3. Gradients of plankton distribution along the length of the loch were dependent on the recent wind history. The direction of the gradient could readily reverse with a shift in wind d irection. These results indicate that the horizontal distribution of p lankton in Loch Ness is more dependent on wind-induced water circulati on patterns than on differential growth of plankton in water masses of differing chemistry.