The horizontal distribution of plankton in a deep, oligotrophic lake—Loch Ness, Scotland

Abstract

SUMMARY1. The horizontal distribution of plankton in Loch Ness, a deep, oligotrophic lake with a simple trench morphometry, was studied on three occasions 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 variability was found to be greatest for the metazoan zooplankton and for the algae, especially two cryptomonad flagellates. Bacteria and heterotrophic protozoa showed relatively little horizontal variability. The degree of horizontal variability was not sufficient seriously to affect 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 direction. These results indicate that the horizontal distribution of plankton in Loch Ness is more dependent on wind‐induced water circulation patterns than on differential growth of plankton in water masses of differing chemistry.