The role of Argopecten purpuratus shells in structuring the subtidal benthic communities of Bahia Paracas, Peru.

GAMARRA A.; LOMOVASKY BETINA JUDITH; IRIBARNE O.; MENDO, J.

Lima

Simposio; CENSOR Endterm Symposium; 2008

In the Peruvian upwelling system there is a high population increase of the scallops Argopecten purpuratus in the subtidal of soft bottom during El Niño periods. The shell beds of dead animals can generate new habitats to be re-colonized affecting the benthic community structure. Shell inclusion experiments performed in the subtidal of Bahía Paracas, Peru, were used to evaluate the effect of different densities of valves of A. purpuratus on the (i) settlement of other species on the shell beds (epifaunal) and, (ii) on the infaunal organisms. Ours results, of bimonthly samplings (December 2006 to June 2007), indicated that a total of 21 species of invertebrates was registered in the different treatments (area with 100%, 50%, 0% of cover by shell) and the untreated areas (0%, 50% of cover by shell). The representative groups were Crustacean (Eurypanopeus transversus, Alpheus spp), Polychaetes (Lumbrineris spp., Nereis spp) in epibenthic organisms and infaunal. There was no significant difference in the number of species (K-W test, H= 2.94, p> 0.05), the abundance by species (K-W test, H= 0.23, p> 0.05), biomass by species (K-W test, H=3.84, p>0.05) and diversity (Shannon index, K-W test, H=2.60, p> 0.05) for the epibenthic organims and infaunal between treatment and untreated areas, however, in treatments cover by shells the number species increased at the starting of experiments (60 days) and then declined gradually (K-W test, H=5.58, p<0.05, MW- U test p <0.05), registering the same in abundance (K-W test, H=11.33, p<0.05). The biomass of epibenthic organisms and infauna showed no significant difference in the sampling dates (K-W test: H=7.31, p>0.05). Eurypanopeus transversus and Nereis sp were registered as epibenthic organisms with important abundances at 60 days of the experiment starting, declining gradually during the sampling dates, however, only E.transversus showed differences between the treatment and untreated control, showing higher abundance in places with accumulation of shells (K-W test, H=13.03, p<0.05, MW-U test p<0.05). Lumbrineris sp was often observed as infaunal organism, and their abundance varied significantly at 180 days of the experiment starting (K-W test, H=7.96, p<0.05; MW-U test p<0.05), however, did not show differences between treatment and untreated controls (K-W test, H=0.64, p>0.05). In conclusion, the beds of shells act as substrate to some epibenthic sessile organisms (cirriped, crepidulas and actinia), and give refuge to mobile organisms (crabs, wandering polychaetes and mollusk), nevertheless, the infaunal organisms (e.g., polychaetes) are favored.