Benthic trophic dynamics in California coastal basin and continental slope communities inferred using inverse analysis

Abstract

The isolation of the deep-sea benthos makes it difficult to measure more than a few elemental transformation rates in a given ecosystem. The measurements usually made include the transfer rates of such biologically important materials as oxygen, particulate carbon, and ammonia between water and sediment. We have developed inverse analysis techniques that produce descriptions which include material flows between trophic groups within the sediments. The techniques use a limited set of process rate and biomass measurements and known physiological and chemical information. Estimated material flows include rates of consun~ption, production, respiration, excretion, and egestion of the major trophic groups in benthic food webs. We analyzed benthic communities in a lowoxygen environment (Santa Monica Basin) and in a higher-oxygen environment on the conhnental slope (Patton Escarpment), both bordering southern Cahfornia (USA). The inverse analyses suggested that the low oxygen community was dominated by anaerobic protozoa and bactena and supported only a small populations of grazers. The dominance of bacteria with high growth rates caused sedimentary detrital carbon and nitrogen there to decompose in a few days. The Patton Escarpment community, overlain with oxygen-rich water, had a more complex food web dominated by the higher trophic level protozoa, meiofauna, and macrofauna. We suggest that carbon and nitrogen were retained in the biomass of these larger grazers for months. The analyses showed that grazers and microbial organisms speciahze in using resources of different nutritional quality. Specialization of this type may have led to a more complete oxidation of sedimenting detritus at Patton Escarpment than at Santa Monica Basin. Organisms in both food webs had low gross production efficiencies that averaged 10 % at the Patton Escarpment and 7 % at the Santa Monica Basin sites. These results suggest that inverse analysis can be a powerful tool to analyze benthic communities.