Diel variations in Acartia tonsa feeding, respiration and egg production in a Mediterranean coastal lagoon

Diel feeding rhythm of copepod size-fractions from Coliumo Bay, Central Chile

“…The observed feeding rhythm was consistent with studies that describe circadian feeding rhythms in several species (i.e. Mackas and Bohrer, 1976;Baars and Oosterhuis, 1984;Durbin et al, 1990;Castro et al, 1991;Checkley et al, 1992;Cervetto et al, 1993), and also agrees with the persistence of circadian feeding rhythms in copepods under non limiting food supply or constant illumination (Petipa, 1958fide Stearns, 1986Mayzaud et al, 1984;Stearns, 1986;Dagg et al, 1989).…”

“…For example, Acartia clausi displayed flexible feeding, with maximum gut content in either day or night samples according to highest ambient food concentrations Saint-Jean, 1985 fide Cervetto et al 1993). Other species like A. tonsa, though affected by ambient food concentration are primarily nocturnal feeders (Durbin et al, 1990;Cervetto et al, 1993). In the present study, the fact that NF persisted in the presence of abundant food suggests that, at least in Spring in Coliumo Bay, food was not the major concern, but that some other factor, namely predation, could be.…”

“…5 min) to minimize stress to zooplankters. Immediately after the tow, the sample was mixed with carbon dioxide saturated water in equal parts in order to anaesthetize the organisms and prevent the loss of gut contents (Cervetto et al, 1993). Samples were then quickly and gently filtered through a battery of sieves of 200, 500, 1000 and 2000 µm.…”

“…Fluorescence was then measured with a Turner Designs fluorometer before and after acidification. Total gut pigment values (chl a-eq) were corrected by adding 33% to compensate for losses of fluorescence Lopez et al, 1988;Downs, 1989;Cervetto et al, 1993;Peterson and Dam, 1996) and by subtracting the background fluorescence of animal tissues (estimated from cope- pods representative of Coliumo Bay assemblage starved for 24 h in GF/F filtered sea water). Background fluorescence values were less than 0.1 ng chl a-eq.…”

Copepods induce paralytic shellfish toxin production in marine dinoflagellates

“…Accordingly, we could detect a strong inducible chemical response, as well as a significantly increased grazing resistance, in A. minutum when it was exposed to intense grazing by copepods. The density of A. tonsa females used in the induction and feeding preference experiments was in the upper end of what is normally occurring, even if similar and even higher densities of copepods have been observed in the field (Durbin & Durbin 1981;Cervetto et al 1993). However, the results from the density dependence experiment show that increased cell specific PST content was induced also at lower, more commonly encountered, densities of copepod grazers and that the response was positively correlated to the density of grazing copepods.…”