BENTHIC TROPHIC DYNAMICS IN CALIFORNIA COASTAL BASIN AND CONTINENTAL-SLOPE COMMUNITIES INFERRED USING INVERSE ANALYSIS

The isolation of the deep-sea benthos makes it difficult to measure mo re than a few elemental transformation rates in a given ecosystem. The measurements usually made include the transfer rates of such biologic ally important materials as oxygen, particulate carbon, and ammonia be tween water and sediment. We have developed inverse analysis technique s that produce descriptions which include material flows between troph ic groups within the sediments. The techniques use a limited set of pr ocess rate and biomass measurements and known physiological and chemic al information. Estimated material flows include rates of consumption, production, respiration, excretion, and egestion of the major trophic groups in benthic food webs. We analyzed benthic communities in a low -oxygen environment (Santa Monica Basin) and in a higher-oxygen enviro nment on the continental slope (Patton Escarpment), both bordering sou thern California (USA). The inverse analyses suggested that the low ox ygen community was dominated by anaerobic protozoa and bacteria and su pported only a small populations of grazers. The dominance of bacteria with high growth rates caused sedimentary detrital carbon and nitroge n there to decompose in a few days. The Patton Escarpment community, o verlain with oxygen-rich water, had a more complex food web dominated by the higher trophic level protozoa, meiofauna, and macrofauna. We su ggest that carbon and nitrogen were retained in the biomass of these l arger grazers for months. The analyses showed that grazers and microbi al organisms specialize in using resources of different nutritional qu ality. Specialization of this type may have led to a more complete oxi dation of sedimenting detritus at Patton Escarpment than at Santa Moni ca Basin. Organisms in both food webs had low gross production efficie ncies that averaged 10 % at the Patton Escarpment and 7 % at the Santa Monica Basin sites. These results suggest that inverse analysis can b e a powerful tool to analyze benthic communities.