Zooplankton spatial distribution along the South African coast studied by multifrequency acoustics, and its relationships with environmental parameters and anchovy distribution

Abstract

Abstract Lebourges-Dhaussy, A., Coetzee, J., Hutchings, L., Roudaut, G., and Nieuwenhuys, C. 2009. Zooplankton spatial distribution along the South African coast studied by multifrequency acoustics, and its relationships with environmental parameters and anchovy distribution. – ICES Journal of Marine Science, 66: 1055–1062. The Central Agulhas Bank (CAB) is an important component of the southern Benguela ecosystem. Despite relatively low primary production, secondary production supports large populations of mid-trophic-level pelagic fish. Exhaustive sampling of the Agulhas Bank ecosystem was performed during a routine acoustic biomass survey in November 2006. A TAPS-6 was deployed with near-simultaneous, plankton-net sampling. Concurrent collections of fish-school and environmental data permitted a detailed study of the water column. Zooplankton was classified by equivalent spherical diameter (ESD; mm): 0.0–0.35 (Class I), 0.35–0.8 (Class II), 0.8–2 (Class III), and >2.0 mm (Class IV). Clear relationships with environmental parameters were only evident at night on the CAB (west of 23°E) for Classes II and III. Class III exhibited pronounced diel vertical migrations, whereas Class I exhibited a reverse pattern. Also observed were the effects of anchovy predation on small zooplankton aggregated in areas of high chlorophyll a.