To understand coral-reef zooplankton ecology on a diel basis, zooplankton abundance, biomass and size composition from a fringing coral-reef of Redang Island, Malaysia, were investigated at three-hour intervals for a 48 hour period. Zooplankton was collected vertically and size-fractionated into three size-classes; 100-200 mm, 200-335 mm, and Ͼ335 mm. Diel variation of the zooplankton showed that the catches at night were always higher than those in the daytime and the nocturnal increase

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... d most strongly in the large fraction (Ͼ335 mm). Zooplankton abundance steeply increased just after sunset, showed an abrupt increase 1.5 hour later and declined sharply thereafter. Observation of diel variation in coral-reef zooplankton from three-hour intervals revealed that the temporal variation was large in this study.