Basin-scale latitudinal patterns of copepod grazing in the Atlantic Ocean

Abstract

Size-fractionated copepod abundance and ingestion rates were investigated along a 50°S-50°N latitudinal transect, during the Atlantic Meridional Transect (AMT) 4, 5 and 6 cruises (boreal spring-autumn 1997, boreal spring-summer 1998). Copepod abundance was higher at high latitudes in spring, near northwest Africa, in the equatorial and Benguela upwelling systems, and in the Subtropical Convergence, and lower in oligotrophic gyres. Gut contents were not related to phytoplankton biomass or production. Gut evacuation rate averaged 0.03 min -1 , and was not related to latitude or body size. Conservative estimates of copepod community total ingestion rates ranged between 3.4 and 173 mg C m -2 day -1 for AMT4, 1.6-252 mg C m -2 day -1 in AMT5 and 10-160 mg C m -2 day -1 in AMT6. Maximum values were always in the upwelling regions, the subtropical convergence and high latitudes in the Northern Hemisphere during boreal spring. Calculated ingestion rates translate into average daily minimal consumption values of 2. 07%, 1.89% and 2.6% of total chlorophyll stock, or 8. 02%, 14.5% and 12.9% of total primary production ingested daily on AMT4, 5 and 6 respectively. Grazing impact increases considerably if we consider ingestion of phytoplankton larger than 2 μm, especially under the influence of the Equatorial and North African upwellings, where copepod ingestion represents up to 30% of the biomass and >100% of production by large cells.