Feeding of Mesopodopsis slabberi (Crustacea, Mysidacea) on naturally occurring phytoplankton

Abstract

Laboratory stu&es on Mesopodops~ss labben feeding on phytoplankton occurnng naturally in Algoa Bay, South Afnca, were run in order to determine Ingestion rates in vanous monospecific phytoplankton concentrabons and to determine possible differences between rates of ingestlon between sexes, size classes, and day/night feeding on 2 dlatom species Increasing food supply was accomparued by a hnear ingestlon response dunng the first 3 h of feed~ngw ~thouct lear upper or lower thresholds Minlmal ingesbon followed this lnitial penod of active feed~ng M slabben, when offered mlxtures of Anadus birostratus and AstenoneUa glaaahs, selected the numencally dominant diatom A glaaahs forms a large splral colony of cells and data suggest size selectivity, as it was selected for by M slabben when numencally domlnant (cells ml-l) in the mlxture even though the number of colonles was less than the number of A birostratus cells present Assoclatlon between apparent shoreward migration by M slabben to close outs~deth e breaker line at night and the distnbutlon of food matenal by np current circulation is postulated The possib~lltles of selective grazing by M slabben influencing phytoplankton community structure, and the possible exclusion of persistent diatom accumulahons behind the breaker line through grazing pressure are noted