A unique subtidal vermetid reef formation in a nuclear power plant discharge area at Ilha Grande Bay (southwestern Atlantic Ocean)

Abstract

Background: The reef-building vermetid Petaloconchus varians is a dominant species on the intertidal zone of rocky shores at Ilha Grande Bay (Rio de Janeiro State, Brazil). Methods: On August 2010, subtidal vermetid reefs were collected in the nuclear power plant discharge area at Ilha Grande Bay. The characteristics of the subtidal reefs were investigated, being described their formation, density and range extension. Results: These are monospecific reefs formed by dense clusters of P. varians, developing mainly by peripheral growth on the rims of most of the bottom rocks resembling "microatolls". The reefs were recorded spreading over about 1,000 m2, restricted to the nuclear power plant discharge area, under continuous influence of waterflow currents (30 cm.s-1), high temperature (>36 °C) and chlorine inputs. Conclusion: It is a unique subtidal P. varians reef formation in the nuclear power plant discharge area at Ilha Grande Bay, with unprecedented records in the Brazilian coast.