Spatio-temporal variability of phytoplankton in the southern Benguela upwelling system

Abstract

The overall spectrum of phytoplankton heterogeneity within the southern Benguela is classified and presented on the basis of spatial and temporal scales, ranging from the macro- to the microscale. State variables in terms of floristic and biomass changes and rate variables in terms of physiological changes are reviewed and related to the physical and biological mechanisms important to their generation and maintenance. Biological and physical processes acting alone and in concert give rise to the spatial and temporal patterns of phytoplankton distribution, making categorization by causative mechanisms both difficult and artificial. Nevertheless, all scales and types of patchiness in the southern Benguela are strongly influenced by the hydrodynamic process of upwelling, both through redistribution of existing biological variability and through the creation of spatial variability in the richness and suitability of the physical and chemical environment. Physical influences override biotic interactions during upwelling whereas, with the onset of stratification, physical processes become less dynamic, allowing biological and chemical factors to become the major determinants of phytoplankton variability. These observations are spatially confirmed, with physical forcing dominant close to the source of upwelling and biological influences more important downstream of upwelling. © 1992 Taylor & Francis Group, LLC.