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Noctiluca scintillans, a heterotrophic dinoflagellate responsible for most of the red tides in Hong Kong waters was investigated to determine the influence of biotic and abiotic factors in determining its population dynamics. N. scintillans first occurred in January when temperature was ~17°C, and reached a maximum of 1980cellsL-1 one month later. N. scintillans interacted with trophic compartments from picoplankton to mesozooplankton, but its population development was largely related to the availability of phytoplankton, especially diatoms. Growth rates in microcosms (with mainly biological factors) ranged from -0.38 to 1.11d-1 and were similar to the field in situ growth rates (physical and biological factors). Thus, optimum hydrographical conditions (temperature and water stability), and a rich food supply were necessary for N. scintillans to bloom. Its spatial distribution pattern was a result of biological and physical coupling, but mainly controlled by physical accumulation processes such as winds, tides and currents.

We examined if the results of statistical analyses of the relationship between copepod communities and water masses would be affected by the mesh size of the plankton net, by comparing abundance and species composition of copepods in plankton samples collected by plankton nets of different mesh sizes. Our samples were collected during the summer of 2006 in the East China Sea (ECS) by plankton nets with mesh sizes of 100 and 330 μm. The abundance of copepods collected by the 100 μm-mesh plankton net was about two orders of magnitude higher than that collected by the 330 μm-mesh plankton net. The difference in abundance was mainly due to the loss of small-sized copepods in the samples collected by the plankton net with the larger mesh. Species richness was higher in samples collected by the 100 μm-mesh net and Piélou's evenness was generally higher in samples collected by the 330 μm-mesh net. Although species composition of copepods varied in samples collected by plankton nets with different mesh sizes, the statistical analysis of the relationship between the copepod community and the water masses in these samples appeared not to be affected.

Mesozooplankton play an important role in transporting energy from microphytoplankton and microzooplankton to higher trophic levels. However there were few studies on the diel feeding patterns and prey selectivity of mesozooplankton. We conducted feeding experiments of mesozooplankton in the East China Sea to determine their respective diel feeding patterns on diatoms, ciliates and dinoflagellates, and to assess the contribution of these prey items to mesozooplankton diet. The results showed higher mesozooplankton grazing rates on ciliates and dinoflagellates than on diatoms at the day time, and the opposite pattern at the night time. A significant prey selection was observed, in which mesozooplankton positively selected ciliates and dinoflagellates during day and diatoms at night. The different grazing reactions of mesozooplankton toward each prey item might be related to the mobility of the prey. In all, microzooplankton (ciliates and dinoflagellates) provided the majority of the mesozooplankton carbon ingestion, even at a station dominated by small pennate diatoms. In particular, dinoflagellates are an important prey of mesozooplankton in the East China Sea and their contribution to the diet of mesozooplankton is unproportionate to their abundance.