Dinâmica de comunidades bentônicas do entremarés de costões rochosos como instrumento de monitoramento de efeitos de eventos extremos no Sudoeste do Atlântico

Abstract

The benthic communities in rocky coastal environments have been indicated to be highly vulnerable to extreme events associated with climate change. Although it is well-established in the literature these recordings and the limits that define an extreme event are rare in tropical areas. In this work climatic and oceanographic data were collected from 6 weather stations between 19º21' S and 25º30' S, and from the oceanographic data base gained from the monitoring float of Rio de Janeiro (RJ-3) in order to delimit meteo-oceanographic values that define an extreme climatic event and their application on Atlantic Southwest benthic communities’ studies. Through the frequency distribution of data were selected the range corresponding to 1% (percentile 99) of the highest and/or lowest values that depending of the variable returned the following limits for extreme events: Precipitation greater than 42 mm.day-1; Air temperature greater than 29.8ºC and below 9.2ºC; Wind speed greater than 3.3 m.s-1; Direction of winds with concentration in one quadrant or unusual quadrants, such as East and West in some locations; Sea surface temperature above 31°C and below 17.7°C; Maximum wave height greater than 4.06 m; Significant wave height greater than 2.54 m and wave periods greater than 9.2 m.s-1. The structure and dynamics of intertidal communities on two rocky coasts located in the region of Ilha Grande, RJ, were also evaluated: the rocky coasts of the Dois Rios and Jorge Grego coves, seeking to associate these two processes. To do this, we applied the method developed by the Rede de Monitoramento de Habitats Bentônicos Costeiros – ReBentos that divides the rocky coasts in 5 vertical transections that have been monitored since 2014. In each transect, quadrats were demarcated and photographed periodically. In this study, the quarterly sampling intervals of the years 2022 and 2023 (August 2022, November 2022, February 2023 and July 2023) and biannual (dry and rainy period) of the years 2018 and 2019 (September 2018 and August 2019) of the distribution ranges of Chthamalus bisinuatus, Tetraclita stalactifera and Petaloconchus varians were used. The sampling was carried out quarterly, using photographs of the quadrats, from which the identification and quantification of sessile species were made estimated by the percentage of coverage in each quadrat. The most reported effects of extreme climatic conditions on benthic communities are the occurrence of mass mortality events and changes in community structure, mainly in response to extreme values of air or water temperature, and the action of storm waves. Among these effects, it was possible to identify that, during the monitoring of an extreme wave action in Dois Rios, in August 2019, we recorded the ecosystem in the beginning of the secondary succession process. AtJorge Grego, no event like this was observed. The occurrence of extreme events has not only intensified but has undergone combinations that cause changes in the structure of benthic communities and therefore their monitoring is increasingly necessary.