Branqueamento de corais e mudanças ambientais: estudo de caso de 3 anos no Atlântico Equatorial

Abstract

Biodiversity and complexity of reef-building corals is remarkable in tropical marine environments. However, the degradation of reefs by local impacts and climate change has been widely confirmed. Despite the socio-economic and ecological importance, the reefs of the Equatorial Atlantic have insufficient knowledge about the relationship between coral bleaching and environmental changes. These reefs have peculiarities as high and constant temperatures, often murky waters, occurrence of high wind speeds, sedimentation and the occurrence of species of resilient corals. Based on this theoretical context, it sought to carry out a monitoring of coral bleaching and analyze the relationship with environmental factors such as sea surface temperature (SST) wind speed, depth and insolation. Data collection was performed in a reef environment located in semi-arid coast of Brazil (Ceara, Northeastern). Bleaching data were collected with scuba diving over 3 years a fotoquadrat method being used at different depths (2m, 4m and 6m). The results suggest that the reef environment under analysis consists of a monotypic assembly of young colonies of the coral Siderastrea stellata; species to be highly resilient to temperature, turbidity and sedimentation. In the analyzed period (2013-2015) did not occur anomalies in SST. Nevertheless, there was bleaching throughout the whole year, but with variable rates (44.3% -84.34%). This denotes that the area is subjected to chronic stress of environmental factors. A more intense bleaching main event is situated in the first semester (May and June). This event is associated with an increase in the SST and the drop in wind speed, which increases the transparency of the water and consequently increases the exposure to solar radiation, mainly in the shallow zone (2m deep). Near the end of each year (October-December) has been an increase in bleaching rates. Possibly it is associated with reduced cloudiness and turbidity, which increases the exposure to insolation. It can be concluded that the solar radiation and SST factors may act as causative factors in bleaching events. The turbidity, cloudiness, depth and increased wind speed (by increasing turbidity) can act mitigating the negative effects of insolation. In literature the turbidity is usually connected to deleterious factors in corals, including increased bleaching. The new results show that the resilience of the semi-arid coast coral of bleaching generates different responses to environmental factors compared to other reef environments set in tropical regions of the world.