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RESEARCH PRODUCT

Short-term variability of mesozooplankton in a Mediterranean Coastal sound (Stagnone di Marsala, Western Sicily)

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description

Short-term variations in mesozooplankton were studied during four 24-h periods at one station in a Mediterranean coastal sound (Stagnone di Marsala, western Sicily) in May, July and October 1996 and March 1997. Zooplankton samples were collected every three or six hours with a plankton net (mesh size 125 µm) towed horizontally at the surface. Hydrometric data (height of tide, speed and direction of current) were also recorded to assess the influence of the hydrodynamic conditions on fluctuations in zooplankton abundance and changes in population structure. The zooplankton assemblages were markedly dominated by copepods and their naupliar stages, which consistently accounted for more than 95% of the total numbers. Peaks in abundance were always recorded at night, due to the increase in coastal forms (mainly of the genus Acartia) and to a lesser extent in autochthonous forms (harpacticoids).The short-term variability of zooplankton seemed to be related both to hydrodynamic factors (tidal and wind-driven currents) and to the nocturnal upward migration of organisms.