Estimates of phytoplankton and bacterial biomass and production in the northern and southern Benguela ecosystems

Abstract

Available data on phytoplankton and bacterial abundance and production off the coasts of southern Africa (to the 500 m depth contour) have been assembled and analysed for a network analysis of carbon flow in the Benguela ecosystem. Phytoplankton carbon biomass (from measurements of chlorophyll a) in the northern Benguela (2 558 300 tons) was considerably higher than in the southern Benguela (671 420 and 516 400 tons for the West and South coasts respectively). However, overall annual production (from C14-uptake measurements) was similar, 77 416 608, 76 399 973 and 78 988 020 tons C·year−1 respectively. Phytoplankton respiration and sedimentation losses were calculated as functions of primary production and therefore followed similar trends. From the most conservative estimates (mean bacterial biomass of 10 mg C·m−3 and average P:B of 0,2·day−1) bacterial biomass is 2–7 per cent of phytoplankton biomass in the northern and southern Benguela, and bacterial production is 3–5 per cent of primary production. A...