Monitoramento da saúde de corais em recifes costeiros e oceânicos utilizando modelos 3-D

Abstract

Due to their proximity to more populated areas, coastal reefs can be more prone to the effects of local anthropogenic impacts than oceanic reefs. The response of corals to these impacts will depend on the species but also on environmental variables such as depth, temperature and exposure to light, determined by the local dynamics of each ecosystem. Comparing coral health between coastal and oceanic environments, within the same latitudinal range, can inform how anthropogenic impacts and the ecosystem´s natural dynamics affect coral health. We monitored colonies of the corals Siderastrea stellata (~ 5m deep) and Montastraea cavernosa (~ 30m deep) on coastal (Rio Grande do Norte; ~ 5 ° S) and oceanic (Fernando de Noronha; ~ 3 ° S) reefs in northeastern Brazil, where these species are among the main reef builders. We monitored 53 colonies of S. stellata and 28 of M. cavernosa quarterly for one year (2018-2019), using three-dimensional models generated from photogametry. From the models, we quantified the percentage of coral surfaces presented bleaching, mortality, disease and algal overgrowth, as indicators of coral health. Both monitored species presented good health status in coastal and oceanic reefs, with no record of intense bleaching during the monitored period, except for one of the oceanic reef environments that experienced an expressive burial event due to the local dynamics. Colonies of S. stellata, remained generally healthier in coastal areas than in oceanic areas, which may be related to less exposure to light in coastal areas compared to oceanic reefs. The health status of M. cavernosa was stable and, despite differing between coastal and oceanic areas, the corals in all monitored sites had, on average, 80% of their surface in a healthy state indicating relatively stable health conditions. The water temperature was also similar and relatively constant in coastal and oceanic reefs. Coral health was more affected by variations in the local ecosystem (e.g. natural burial) than by proximity to human impact, indicating that natural local dynamics needs to be accounted when assessing the response of corals to human impacts.