Distribuição, recrutamento e sobrevivência do coral pétreo Siderastrea stellata (Verrill, 1868) em um recife arenítico do Atlântico Sul

Abstract

Reef ecosystems are known worldwide for their natural beauty and their capacity to harbor a great variety of marine life. In addition, these environments provide goods and services that encompasses social, environmental and economic spheres. However, around 20% of the world's reefs have been destroyed and 35% are threatened. In Brazil, the reefs are located along the northeast region and are usually near the coast, enabling the access of the human populations that use them for food, sport and recreation. One way to maintain reef resilience and avoid biodiversity loss would be to gather information on recruitment and survival of organisms from reef communities. The endemic hard coral, Siderastrea stellata, is one of the most resistant and common species in Brazilian reefs. Considering the ecological importance of this species of coral, we aimed to understand some aspects of its distribution, recruitment and colony maintenance. Therefore, S. stellata colonies were analyzed at different study sites in the “Parracho de Pirangi/RN”. The following activities were performed: 1) mapping colonies size (Chapter 1), 2) running recruitment experiment subjected to manipulation of calcareous algae (rhodoliths), testing the hypothesis that rhodoliths act as facilitators due its complex three-dimensional structure (Chapter 2), and 3) running a health evaluation experiment of juvenile colonies in different areas of the reef, through macroalgae manipulation, testing the hypothesis that coral colony health is affected negatively by the presence of benthic macroalgae (Chapter 3). A distribution pattern in Parracho de Pirangi/RN was observed with less coral occurring in the area nearby touristic site. It is possible that impacts such as the constant suspension of sediments caused by swimmers and boats are acting as the main mechanism driving this distribuition pattern. Coral recruitment of Parracho de Pirangi was low compared to other shallow reefs from northeastern Brazil. This shows that although very resistant, the coral S. stellata is not able to establish on this reef formation. It was also noted that recruitment is not facilitated by calcareous algae that form rhodoliths. Instead, rhodolith banks sheltered abundant concentration of benthic invertebrates that might compete for space or feed on coral larvae, preventing recruitment. Generally, the health of young colonies was affected by bleaching, which increased throughout the year. This increase was correlated with low water salinity registered. However, it was notable that bleaching was lower in the treatment where benthic macroalgae was not removed. Possibly, the growth of benthic macroalgae within the limits observed over the months attenuated the effects of high solar radiation on young coral colonies, protecting them from bleaching.