A study of rotifers in the River Thames, England, April-October, 1996

Abstract

More than 30 species of rotifer were recorded in the River Thames between Inglesham and Reading from April to October, 1996. Seven of these were relatively abundant. These were Keratella cochlearis (Gosse), Synchaeta oblonga (Muller), Polyarthra dolichoptera Idelson, Keratella quadrata (Muller), Brachionus angularis Gosse, Euchlanis dilatata Ehrenberg and Brachionus calyciflorus Pallas. In early spring, there was little variation in rotifer density along the river, but a marked downstream increase in abundance developed later in the year. Mean rotifer densities ranged from 24 ind. 1-3 at the upstream site to 700 ind. 1-1 at the most downstream site. A maximum total rotifer density of 4160 ind. 1-1 was recorded at Reading on 29 July 1996. In general, the downstream increase in rotifer abundance seemed to parallel similar increases in chlorophyll a concentration in the river water. Losses due to invertebrate predation were probably low, but fish gut analyses from an earlier study had suggested that rotifers may be an important food source for larval fish. Throughout the study, rotifer samples were collected and prepared for counting by two different methods. The results show that estimates of rotifer density may be significantly affected by sampling method.