A carbon flow model and network analysis of the northern Benguela upwelling system, Namibia

A carbon flow model was constructed of the northern Benguela upwelling ecosystem. The model consists of 22 living and two non-living compartments, depicting the biomass of each compartment and the rates of exchange between them. The only primary producer in this system is phytoplankton, whilst bacteria, heterotrophic microflagellates and microzooplankton form part of the microbial loop. Primary consumers include mesozooplankton, macrozooplankton and jellyfish, while the fish community consists of anchovy, pilchard, lanternfish, gobies, horse mackerel, bake, snoek, benthic feeding fish and other carnivorous fish. The top consumers are seabirds and seals. The primary production-zooplankton-pelagic fish-demersal fish energy flow pathway appears to dominate in this system, with jellyfish, pilchard and horse mackerel being the most important planktivores. Jellyfish appears to be an important component in the system due to its high biomass and consumption of about 10% of the primary production. Hake is the most important secondary consumer. The carbon flow model was analyzed by means of network analysis, and the results show a total system throughput of about 88897 mg C m(-2) day(-1), a development capacity of 38 041 mg C m(-2) day(-1), an ascendancy value of 17 313 mg C m(-2) day(-1), that about 7% of the total system throughput is recycled on a daily basis, and that the internal relative ascendancy is about 44%. These results were compared to similar data from other systems such as the southern Benguela and the Peruvian upwelling systems. (C) 2000 Elsevier Science B.V. All rights reserved.