Carbon Budget and Network Analysis of a High-energy Beach/Surf-zone Ecosystem

A carbon budget, compiled for a high-energy beach/surf-zone ecosystem in South Africa, consists of 14 living and two non-living compartments, namely dissolved organic carbon and suspended particulate organic carbon. The living compartments constitute three trophic assemblages; the microbial loop, the interstitial system and the macrofauna. The food web budget was subjected to network analysis to assess the status of the system. Input–output analysis indicated that the microbial loop is the most important trophic assemblage in this system, with the interstitial assemblage second in importance. Lindeman trophic analysis estimated that detritivory amounts to 868 mgC m−2day−1and the detritivory:herbivory ratio is 13:1. Biogeochemical cycle analysis concluded that this system is not under any anthropogenic stress, having a nexus with 48 cycles, three 24-cycle nexuses, a single cycle including 11 compartments, and only seven single-cycle nexuses. Based on global systems’ properties, this ecosystem has a high normalized internal ascendency (Ai:Ci) which suggests that it is well organized and stable. The system possesses significant internal stability and resistance, a feature that is expected from a physically controlled environment. The relative ascendency (A:C) of this system falls well within the range of relative ascendencies for other systems, being higher than most estuaries but lower than upwelling systems, bays and seas. Overall, this ecosystem is perceived to be unstressed and mature, with the physical control exerted on it providing significant internal stability.