PALEOECOLOGY OF A ROCKY SHORE ENVIRONMENT IN THE LATE PLIOCENE, PLAYA HUACLLACO, PERU

Fossiliferous rocky shore deposits at Playa Huacllaco, coastal Peru, were examined to determine changes in composition and diversity of barnacles and mollusks through a Late Pliocene section. Well-preserved rocky shore fauna are rare in the fossil record, and few studies have been published on temporal changes in diversity with this intertidal environment. Bulk samples collected from a section measuring 60 stratigraphic meters at Playa Huacllaco were sieved for barnacle opercular plates and mollusk fragments, which were counted and identified. Samples were collected from transported assemblages composed mainly of barnacle debris, ranging from completely disarticulated to displaced barnacle clusters and balanuliths. Barnacles dominate the faunal assemblages, typically accounting for ~90% of the individuals counted, although molluscan diversity is often greater. Scuta plate ratios were used to determine relative barnacle species diversity within the section. Six species of barnacles were identified, and there is an abrupt change in barnacle diversity halfway up the section. In the lower half of the section, diversity is relatively even between the three major species, Balanus laevis nitidus, Balanus tintinnabulum, and a currently undescribed species. In the upper half of the section, diversity is dominated by Balanus laevis nitidus, and the undescribed species disappears from the section. Noncorresponding changes in gastropod taxon diversity can be seen through the section, mainly as speciation events. No recordable change is observed in the bivalve taxa. This data and further studies can be used to observe changes in community composition of rocky shores over long periods of time.