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Seasonal and vertical variation of macrozooplankton biomass in the Mochima Bay, Sucre State, Venezuela, during 1997-1998

Abstract:

The role of macrozooplankton in Mochima Bay was studied examining its biomass and its relationships with some environmental parameters during 1997 and 1998. Water transparency was measured with a Secchi disk; water samples were collected with a Niskin bottle (5 L) to determine: temperature, dissolved oxygen and phytoplankton biomass in two stations. Macrozooplankton horizontal samples were collected with a net (mesh size 555 μm and 0.25 m in diameter) at 0-5 and 10-15 m in two stations, one external (Est. A) and other internal (Est. B). Macrozooplankton biomass was estimated in terms of displaced volume and dry weight. The periods of maximum macrozooplankton biomass occurred between March-May and October-December for both years; the minima occurred in July-September. The highest biomass values were measured at the inner station and in the deeper layer (10-15 m). Maximum values for phytoplankton and macrozooplankton biomass coincided with periods of higher upwelling and wind intensity; these values were higher in 1997 than in 1998. The results follow pre-established patterns but also show high annual variability in phytoplankton and zooplankton biomass.