ENRICHMENT, DISTURBANCE AND DEEP-SEA COMMUNITY STRUCTURE: THE SIGNIFICANCE OF LARGE ORGANIC FALLS TO BATHYAL BENTHOS IN SANTA CATALINA BASIN (CALIFORNIA, POLYCHAETES)

The Submersible ALVIN and free-vehicle cameras were used to measure standing crop, faunal utilization and benthic community effects of nekton carcasses and Macrocystis pyrifera parcels at 1300 m in Santa Catalina Basin (SCB), off California, USA. Energy flux in the form of nekton falls was roughly estimated to be 8.1 x 10('3) cal m('-2)yr('-1): enough to meet about 5% of the respiratory requirements of the benthos. Parcels of dead fish on the seafloor attracted large aggregations of fish and invertebrate scavengers which consume the carrion parcels within days. The most strongly attracted megafaunal species was the abundant ophiuroid Ophiophthalmus normani, which achieved densities of 700 m('-2) and remained at elevated abundance for weeks. Six other megafaunal species also feed on carrion, including two common epibenthic invertebrates. These scavengers consumed fish parcels so rapidly and dispersed so broadly that energy from nekton falls reaches infaunal benthos only in attenuated form, yielding minor community enhancement.;Combined standing crop and utilization rate estimates yielded a detrital kelp flux of 950 cal m('-2) yr('-1): enough energy to supply 0.6% of benthic respiratory requirements. Eight megafaunal species were attracted to Macrocystis parcels resting on the seafloor; five species fed on kelp or its associated microflora. The infaunal community showed little response to detrital kelp on time scales up to 6 weeks, and kelp falls appear to be relatively unimportant in structuring the SCB infaunal assemblage.;The predominant infaunal effect of fish parcels was disturbance, resulting from sediment disruption caused by vigorous feeding activity of megafaunal scavengers. Many species declined following such perturbations: the surface-dwelling community dominant (a cirratulid polychaete) was most strongly disturbed. Three macrofaunal species, two of which were common in the background community, rapidly (within weeks) colonized areas of disturbance/enrichment near baitfalls. All three (a cumacean, a paranoid polychaete and a cirratulid) responded as post larvae, suggesting that "adult" colonization of disturbed habitats is important in deep-sea environments. The opportunistic response of two common species indicates that normal components of the SCB infaunal assemblage rapidly exploit disequilibrium conditions, suggesting that disturbance/enrichment pehnomena contribute to the structure of this and other deep-sea communities.