Coralline Algae Depositional Environments on the Brazilian Central-South-Eastern Shelf

The Brazilian central shelf along the State of Espirito Santo features several palaeochannels eroded into deposits of coralline algae. Seismic profiles and jet-probe cores have shown a layer of calcareous sediments over 10 m thick that is formed mainly by the fragmentation of coralline algae. Video and scuba-diving observations demonstrate that dense aggregations of rhodoliths often change position on the sea bottom as a result of being dragged ("sail" effect) by foliose algae such as Sargassum, Dictyopteris, and Zonaria. The benthic fauna associated with rhodoliths or foliose macroalgae (Hydrozoa and Amphipoda) is dominated by polychaetes, ophiuroids, and molluscs. The sessile fauna is poorly represented, consisting of some sponge species. It was possible to verify the following dynamics: (i) in summer, foliose macroalgae and zoobenthos (phytal) are established upon the rhodoliths; (ii) in early and midwinter, epiphytic macroalgae are senescent; (iii) in late winter, storms disturb sediments on the sea bottom, burying living rhodoliths and removing the foliose algae; and (iv) in spring, a bloom of the bivalvia Pinctata pectinata occurs, overgrowing the bottom. The rhodoliths tend to remain on the seafloor (with 10% to 20% estimated buried and becoming permanently incorporated to the sediment mass). The sediment dynamics are strongly dominated by erosive phases related to storms.