Distribution of Pleuromamma (Copepoda: Metridiidae) along a north-south transect in the Indian Ocean

Abstract

Distribution and abundance of calanoid copepods of the genus Pleuromamma Giesbrecht 1898 along a north-south transect in the Indian Ocean were studied. Seven species such as Pleuromamma indica, P. abdominalis, P. gracilis, P. xiphias, P. quadrungulata, P. piseki and P. borealis were observed. There was a gradual increase in species number from northern latitudes towards subtropical convergence (35 degrees to 40 degrees S). The region between 10 degrees N and 10 degrees S lat. was congenial for distribution of Pleuromamma species. P. indica was dominant and was recorded in large numbers in the oxygen deficient waters (0.02 mu ml dm-3). Diel and ontogenetic migrations were noticed for P. xiphias and P. abdominals. The late copepodids (C 4 and C 5) were abundant in the upper 200 m. The adults were more at deeper depths. The vertical segregation among co-occurring species was observed in the zooplankton collections taken during day. However, there was considerable overlap at night. Sexual segregation was also noticed