FILTER-FEEDING SHRIMPS (ANOSTRACA) GRAZING ON BACTERIA

Streptocephalus torvicornis and Branchipus schaefferi, males and femal es separately, were fed Escherichia coli at densities ranging from 1 x 10(6) to 5.5 x 10(7) ml(-1). These shrimps are able to consume large quantities of E. coli. Branchipus schaefferi consumed 4 x 10(8) E. col i ind(-1) hr(-1) and S. torvicornis consumed 5 x 10(8) E. coli ind(-1) hr(-1) (0.082 mg hr(-1) ind(-1)). Consumption leveled at an initial d ensity of 4 x 10(7) E. coli ml(-1) for B. schaefferi, while for S. tor vicornis consumption leveled at 4.5 x 10(7) E. coli ind(-1) hr(-1). Th e functional response curves of these filter-feeding shrimps showed an unexpected pattern. For the males of both species, at 15 x 10(6) E. c oli ml(-1) there was a small decrease in consumption, while the curves of the females showed a similar decrease at 20 x 10(6) E. coli ml(-1) . This phenomenon is explained by assuming that the distance between t he setae of the limbs, the movement rate of the thoracic appendages, o r the inclination of the filtering apparatus is altered. During 5-h ex periments, both species do not feed at a constant rate.