Community Response to Pulsed Enrichments (Benthic)Studies of naturally or anthropogenically enriched sedimentary habitats have consistently demonstrated negative effects on the fauna normally present in undisturbed conditions. The trajectory of community response to enrichment generally involves a continual decrease in diversity and replacement of the pre-disturbance community with a depauperate disturbance community dominated by a few opportunists (Thrush, 1986; Pearson, 1978; Conlan, 1979; Gray, 1989). The enrichment effects in this study essentially conformed to the general pattern, and did not vary between the material used, but were dependent upon the degree of enrichment.
In all experiments the polychaete assemblage was virtually replaced by a monoculture of Capitella capitata complex (a spionid polychaete remained at much reduced density). C. capitata was not present prior to the enrichments, but large populations exist in sediments enriched with kelp and surfgrass detritus about 600 m from the study site (Vetter, 1995). Even with the likelihood that larvae were immediately available, it is remarkable that the recruits managed to mature and produce eggs in nine days within the plot enriched with fertilizer. The density of C. capitata was high on day 10 of corral experiment #2 in one of the alginate enrichment plots, but no eggs were present. Eggs were present in both alginate plots by day 17 of that experiment.
Such enriched patches may be rare, but they have been demonstrated to be important for the growth and reproduction of opportunistic species (Tsutsumi, 1990) As expected the amphipods were depressed in enrichment plots.
Vetter, E. W. (1996). "Enrichment experiments and infaunal population cycles on a Southern California sand plain: response of the leptostracan Nebalia daytoni and other infauna." Marine Ecology Progress Series 137: 95-101.