Zooplankton biomass and indices of grazing (gut uorescence), respiration (electron transfer syste... more Zooplankton biomass and indices of grazing (gut uorescence), respiration (electron transfer system activity, ETS) and growth (aspartate transcarbamylase, ATC) were studied in relation to an upwelling lament off northwest Africa during August 1993. The lament extended 150 km offshore into the oligotrophic waters. It was generated by a trapped, quasi-permanent cyclonic eddy located between the Canary Islands and the African shelf. High biomass, speci c gut uorescence and electron transfer system activity in zooplankton were observed along the lament structure. In contrast, low values of biomass, gut uorescence, ETS and ATC speci c activities were found in the center of the trapped cyclonic eddy. Assuming a 50% of pigment destruction, the calculated grazing impact of zooplankton on primary production varied between 16 and 97%, a high range compared to other oceanic systems. Ingestion, estimated from indices of metabolism and growth, accounted for 47-296% of the primary production (assuming an herbivorous feeding). Mesozooplankton transported offshore into the oligotrophic area ful lled their metabolic demands with nonpigmented food as observed from the increase of omnivory from the coastal waters to the open ocean. The progressive decay of grazing and metabolic indices along the lament suggests that advection, rather than local enrichment processes, is mostly responsible for the high biomass values in this physical structure.
Zooplankton biomass and indices of grazing (gut uorescence), respiration (electron transfer syste... more Zooplankton biomass and indices of grazing (gut uorescence), respiration (electron transfer system activity, ETS) and growth (aspartate transcarbamylase, ATC) were studied in relation to an upwelling lament off northwest Africa during August 1993. The lament extended 150 km offshore into the oligotrophic waters. It was generated by a trapped, quasi-permanent cyclonic eddy located between the Canary Islands and the African shelf. High biomass, speci c gut uorescence and electron transfer system activity in zooplankton were observed along the lament structure. In contrast, low values of biomass, gut uorescence, ETS and ATC speci c activities were found in the center of the trapped cyclonic eddy. Assuming a 50% of pigment destruction, the calculated grazing impact of zooplankton on primary production varied between 16 and 97%, a high range compared to other oceanic systems. Ingestion, estimated from indices of metabolism and growth, accounted for 47-296% of the primary production (assuming an herbivorous feeding). Mesozooplankton transported offshore into the oligotrophic area ful lled their metabolic demands with nonpigmented food as observed from the increase of omnivory from the coastal waters to the open ocean. The progressive decay of grazing and metabolic indices along the lament suggests that advection, rather than local enrichment processes, is mostly responsible for the high biomass values in this physical structure.
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