DIEL VARIATIONS IN ACARTIA-TONSA FEEDING, RESPIRATION AND EGG-PRODUCTION IN A MEDITERRANEAN COASTAL LAGOON

Short-term changes in abundance, feeding, respiration and spawning by the copepod Acartia tonsa were studied during four 24 h periods at two stations in a Mediterranean lagoon in May and June of 1989 and 1990. Nightly increases of abundance in the upper layer, attributed to noctu rnal upward migration, were observed in three out of the four time ser ies. Nevertheless, occasional daily increases were observed too, so th at no clear diel patterns in abundance could be defined. Contrarily, d iel patterns seemed to appear: (i) for feeding (higher at the beginnin g of the night), based on gut fluorescence and clearance and ingestion rate measurements; (ii) for respiration (lower at night and based on 8 h incubation periods); and (iii) for spawning (higher at the end of the night, based on experimental data). The origin of these patterns, as well as their relationships to environmental data and their possibl e association, are discussed with regard to the available literature.