Diel variation in abundance and size composition of zooplankton community in coral reef area of Bidong Island

Abstract

A study on diel variation was carried out in Bidong Island fringing reef to understand coral-reed zooplankton ecology on diel basis, zooplankton abundance and size composition. The samples were taken for 48 hours with 3 hours interval. Zooplankton was collected vertically with 1 OOμm mesh size Kitahara net and sizefractionated into 100-300 μm and >300 μm. Diel variation of the zooplankton showed that abundance during night was always greater compared to day. Nocturnal increase occurred most strongly in the large fraction (>300 μm). In Bidong Island, the peak of zooplankton is late at night at 3a.m (22976 ± 1339 ind. m-3). Large size fraction (>300μm) zooplankton show strong pattern of nocturnal migration which consist of several species of zooplankton such as polychaetes, appendicularia, nauplius, copepods, arrow worms and ra.diolarian. While for small fraction zooplankton (100- 300μm) most common zooplankton were polychaetes, appendicularia, copepods, bivalvia, gastropodanauplius and ra.diolarian. The highest peak for small size zooplankton was at 3a.m (11557 ± 355 ind. m-3). M-Whitney analysis shows that there were differences in the night and day zooplankton population (p<0.05).