TEMPORAL AND SPATIAL VARIATION IN THE PALEOCOMMUNITY STRUCTURE OF LATE TRIASSIC CORAL REEFS FROM NORTHERN CHILE

The Rhaetian-Hettangian interval records one of the major Phanerozoic extinction events, and the first major crisis to have affected scleractinian reef ecosystems. Most data from this time interval comes from localities in North America and Europe, and much less is known about the Triassic-Jurassic reef ecosystems in other regions. In order to address this geographic bias, we have undertaken a study of the Late Triassic reefs of the Domeyko Cordillera, northern Chile. Sections at Portezuelo de la Sal and Punta del Viento were described and sampled. These two sections are correlated with the Rhaetian Epigondolella mosheri conodont biozone. In order to assess how species composition, abundance and richness varied spatially and temporally, paleoecological data were collected from 7 horizons in each section using 6 randomly spaced 25x25cm quadrats per horizon. Rarefaction curves were produced for each horizon and locality, and correlations between richness and dominance were made. NMDS, ANOSIM and SIM PER routines were used to evaluate the differences in composition within and between horizons, and rank-abundance models were fitted to each community. The Portezuelo de la Sal locality recorded generally higher and more stable richness values through the time, whereas Punta del Viento recorded lower richness values that increased up section. A negative correlation between richness and dominance was observed, especially at Punta del Viento. The spatial species composition changed significantly between locations, with relatively constant turnover at Portezuelo de la Sal compared to increasing turnover at Punta del Viento. A geometric rank-abundance model best fitted the Punta del Viento data, whereas a log-normal model was the best explanation of the species abundance at Portezuelo de la Sal. The paleocommunities in each reef locality seem to have their own temporal and spatial dynamics. In agreement with other studies, those communities act more like ‘metacommunities’ where each subset species ‘patch’ is affected independently by disturbance, habitat distribution and/or environmental gradients, which generate discrete communities through time.