Diel feeding behavior of meiofauna and their relationships with microalgal resources

Diel variation of feeding by ostracods and harpacticoid copepod species on microalgae was examined in a mudflat of a Spartina alterniflora saltmarsh. Feeding (gut pigments and consumption of (14)C-labeled algae) and benthic microalgal abundance and composition (HPLC analysis of photopigments) were measured every 6 h over a 48-h period. Midday feeding peaks were detected in Coullana sp. juveniles and adult females (but not males), Microarthridion littorale, Pseudostenhelia wellsi, and ostracods and were coincident with peaks in microalgal biomass. This pattern of midday feeding peaks by meiofauna differs from classical models of zooplankton feeding, which typically peak at night. Midday feeding peaks were apparently influenced by functional responses to food availability (ostracods and Coullana sp. females and juveniles), entrained diel rhythms (M. littorale), influence of light-positive (M. littorale) or negative (Coullana sp.), and possibly by vertical migration of diatoms within sediment. The negative influence of light on grazing by Coullana sp. may have implications for its feeding activity during midday low tides. Diatoms dominated the benthic microalgae, but cyanobacteria and chlorophytes contributed significantly to the planktonic community. Coullana sp. gut pigments indicate that at least part of its diet is planktonic, but it selectively avoids planktonic cyanobacteria. Diel variation of microalgal biomass appears to be influenced by meiofaunal grazing, which implies that meiofauna represent an important link between microalgal primary production and higher trophic levels.