Pigment signatures of phytoplankton composition in the northern Benguela ecosystem during spring

Abstract

Pigment indices were used to investigate the distribution and composition of phytoplankton in the northern Benguela during the austral spring of 2000, with sampling being conducted on five transect lines between 19°S and 25°S and at other inshore stations on the shelf. Total chlorophyll a concentrations (TChla) at the surface ranged from 18.4mg m−3 at shallow inshore stations to 0.58mg m−3 at offshore localities in deeper water. Phytoplankton communities in the inshore environment were characterised by elevated biomass levels and the dominance of diatoms (high FucDP indices). These diatom populations were associated with cool, higher density, nutrient-rich waters near the coast. Phytoplankton biomass declined with increasing distance offshore and the communities changed to a mixed population where small flagellates were generally dominant (high FlagDP indices). These flagellate communities were associated with warmer, lower density waters. Whereas dinoflagellates (PerDP Index) and prokaryotes (ZeaDP Index) were observed throughout the region, their contribution to the communities was of secondary importance.