Selective feeding of Acartia clausi and Centropages typicus on microzooplankton

Abstract

Selective feed~ng of 2 common copepods, Acartia clausi and Centropages typicus, on mixtures of ciliates and planktonic algae was investigated. Results show the ability of these copepods to recognize the quality of their particulate foods. An equiproportional mixture (in terms of biovolume) of the oligotrichous cihate Strombidium sulcatum and either the dinoflagellate Prorocentrum micans or the diatom Thalassiosira weissflogii was offered to the copepods. The copepods ingested ciliates, at rates of 3.2 X 10' &m3 copepod-' h-' for A. clausi and 4.3 X 105 pm3 copepod-' h-' for C. typicus (67 and 80 % of the total ingested ration respectively), when chate + dinoflagellate mixtures were offered. A. clausi preferred S. sulcatum to T weissflogii, and ingested the ciliate at a rate of 3.7 X 10' pm3 copepod-' h-' (75 O/ O of total ingested ration). The differences observed in the selection of 2 types of prey by copepods were reflected in a positive Ivlev Electivity Index for the ciliates (as high as + 0.73) and in a negative Index for both dinoflagellates and diatoms (as low as -1.00). Ecological implications of this type of selective feeding behaviour in mesozooplankton are also discussed.