Effect of diet on the coupling of ingestion and egg production in the ubiquitous copepod, Acartia tonsa

The ability of consumers to convert ingested carbon into growth is critical for secondary production and trophic transfer. We conducted laboratory experiments to investigate the effect of different prey and concentration on the ingestion rate (IR), egg production rate (EPR) and egg production efficiency (EPE) of the ubiquitous copepod, Acartia tonsa. Experiments were run at several prey concentrations, ranging from 11 to 1132 mu gC L-1, of the diatom Thalassiosira weissflogii, the autotrophic dinoflagellate Prorocentrum minimum, the heterotrophic dinoflagellate Oxyrrhis sp., the flagellate Dunaliella tertiolecta, and the bacterivorous scuticociliate Uronema sp. IR increased curvilinearly with concentration for all diets. EPR also increased curvilinearly with increasing food concentration similar to IR, with the exception of the flagellate diet, for which EPR decreased linearly with food concentration. EPR ranked as T. weissflogii > P. minimum > Oxyrrhis sp. = Uronema sp. > D. tertiolecta. IR and EPR were linearly related, except for flagellate diet. The slope of the carbon-based relationship between IR and EPR, the egg production efficiency (EPE), was highest for the diatom (77.5%) and lowest for the scuticociliate (4.2%). Egg production was not correlated to ingestion of the flagellate offered to A. tonsa. We conclude that of the five prey species, the diatom T. weissflogii is the best prey to promote A. tonsa reproduction, to optimize trophic transfer efficiency, and to increase mass cultivation of this species