Abundance and composition patterns of coastal zooplankton at various temporal scales in a seasonal upwelling cycle in margarita island, venezuela

International audienceZooplankton abundance, biomass and composition were evaluated in various temporal scales in a seasonal coastal upwelling system at Margarita Island, Venezuela. Scales of temporal variation include weeks, months and seasons (relaxation, upwelling and transition). Seasons were delimitated by upwelling index and sea temperature. The sampling period comprise Sept/2002 - July/2003. Zooplankton samplings were made by horizontal trawls (1-10m depth), using 200μm nets, 2-6km from the coastal margin. Total abundance show important variation at week scales, with different patterns between locations, while seasonal differences of abundance are marginal. Biomass only shows seasonal variation due significant reduction in the transition season. Zooplankton assemblages show changes at scale f weeks, with different local patterns, and seasonal changes. Changes in assemblage between the relaxation and upwelling seasons include reduction (during upwelling) of abundance in copepods, cladocerans, salpidae, chaetognates, fish and crustacea larvae. Except by cirripedia larvae, those were important in the upwelling assemblages. Transition shows high variation, with reduction of biomass and assemblage composition similar to upwelling, except by an isolated event. Small scale variation in the zooplankton could be related to physical processes at small scales, eg. turbulence, local circulation, small eddies and filaments, and biological response. Additional sources of nutrient input, eg. riverine input and internal waves, could support local plankton productivity and abundance during relaxation. Detection of high variation in zooplankton abundance and composition at small scales, with local interaction, bring a new light over zooplankton estimation in time series in this system