Cross-shelf observations of diet and diel feeding behaviour of the bearded goby Sufflogobius bibarbatus off Namibia

Abstract

The diet of the bearded goby Sufflogobius bibarbatus was studied at two 48 h stations off the Namibian coast. The inner station (120 m) was characterised by a deep layer of low-oxygen bottom water (<0.5 ml DO l^–1 or <10% oxygen saturation) scarcely inhabited by metazoan animal life. Gobies at this station were ~75 mm total length (TL) and displayed a strong vertical size gradient. The diet of all fish was dominated by sedimented diatoms, and digestion appeared to occur primarily in the oxygen-rich water column at night. By contrast, the environment at the offshore station was characterised by a thin layer of oxygen-poor bottom water, and a richer benthic and zooplankton food environment. Pelagiccaught gobies were significantly shorter (43.3 mm TL) than demersal-caught individuals (99.9 mm TL) throughout 24 h, and the difference in habitat was reflected by differences in diet: pelagic-caught fish ate mostly zooplankton whereas demersal-caught fish ate mostly benthic infauna. In contrast to the situation inshore, digestion appeared to take place throughout 24 h. The results presented here indicate a strong relationship between diet, feeding

Keywords: Benguela upwelling ecosystem, detritus, ecosystem change, foodweb, gut content analysis, sardine, trophic ecology

African Journal of Marine Science 2011, 33(1): 119–126