Ref ID : 1865
Anna Hillbricht-Ilkowska; Response of planktonic rotifers to the eutrophication process and to the autumnal shift of blooms in Lake Biwa, Japan. I. Changes in abundance and composition of rotifers. Jap.J.Limnol. 44(2):93-106, 1983
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The density of planktonic rotifers in Lake Biwa was 100-3,000 ind. L-1 from September to December, 1980. This level is remarkably higher than that reported by Yamamoto (1967, 1968) who noted more than 10-600 ind. L-1, although the northern basin (LBN) has been, in general, regarded as having lower values than the southern basin (LBS). An increase in population density was observed in the following species: 1) Small and fine particle feeders like Keratella cochlearis, Collotheca pelagica, Brachionus species group and K. quadrata and 2) graspers such as Polyarthra vulgaris and P. dolichoptera. The long-term changes may well be evidence for the accelerated eutrophication of Lake Biwa. The actual trophic difference between both basins is reflected in 1) greater abundance of rotifers (maximum value 3,000 ind. L-1); 2) greater contribution of K. cochlearis (esp. f. tecta 50%); and 3) higher Trophic State Index (75) in the LBS; on the contrary, corresponding values were 300 ind. L-1, f. tecta 1% and TSI=46, respectively, in the LBN. During the autumnal shift of the blooms from green algae to diatoms coupled with the autumnal cooling of the water there was a succession of dominant species with food selection of different size particles: K. cochlearis, Polyarthra spp. K. quadrata. In November, a considerable increase in the number of K. cochlearis f. tecta was recognized.