Changes in Rotifer Species Composition and Abundance along a Trophic Gradient in Loch Lomond,Scotland, UK

Loch Lomond is the second largest body of freshwater in Great Britain. It is a long, narrow lake (36.4 km long, 8.8 km wide). The northern basin is fjord-like and surrounded by a mountainous, base-poor, rocky catchment. In contrast, the southern basin is much broader and shallower with a mainly lowland, calcareous, agricultural catchment. This causes a trophic gradient along the length of the loch that runs from the oligotrophic northern basin to the more mesotrophic southern basin. Rotifer samples were collected at monthly intervals between May and October 2002 at three locations along the length of the loch. More than 12 species were found, the commonest of which were Keratella cochlearis (Gosse) and Trichocerca stylata (Gosse). Although the species composition of the rotifer community varied very little among the sites, rotifer abundance increased markedly from north to south, apparently reflecting the trophic gradient along the length of the loch. The results suggest that rotifer abundance may be a more sensitive indicator of trophic state, and changes in trophic state, than species composition.