Feeding activity and swimming patterns of Acartia grani and Oithona davisae nauplii in the presence of motile and non-motile prey

Abstract

The feeding behaviour of the nauplii of the copepods Acartia grani (calanoid) and Oithona davisae (cyclopoid) was investigated in relation to the different motility capabilities of their prey. The prey were the motile dinoflagellate Heterocapsa sp. (equivalent spherical diameter, ESD = 12.8 µm) and the non-motile diatom Thalassiosira weissflogii (ESD = 14.4 µm). Functional response feeding experiments showed that A. grani nauplii exhibited higher ingestion rates on the motile than on the non-motile prey, with maximum daily rations of, respectively, 299 and 185% body C d–1. O. davisae nauplii showed lower ingestion rates (121% body C d–1) and were unable to feed on the non-motile prey. Video observations showed that A. grani nauplii moved with a continuous hopping behaviour, either in a straight or helical pattern; feeding events were observed mainly while swimming in helicoids. O. davisae nauplii exhibited a jump and sink behaviour, typical of ambush feeding. Both species showed changes in their behaviour when presented with the motile prey Heterocapsa sp. This indicates that the nauplii are capable of adjusting their feeding behaviour to the different prey characteristics, thereby optimising ingestion rates