A influência do branqueamento em corais sobre a geoquímica carbonática em uma zona entremarés na costa de Fortaleza-CE

Abstract

Coral reefs are limited to tropical regions such as Africa, Australia and the American continents, which display nutrient-poor waters and high solar incidence throughout the entire year. In recent years, due to the degree of degradation that coral reefs have been experiencing, many researches are focused on conservating these environments and understanding the causes of these impacts along with their relationship with anthropic activities. The most common anthropic impacts in reef environments are marked by actions related to the accelerated growth of urban centers, mainly in the coastal zone. Among these types of contamination are heavy metals, which have a high resistance to degradation and can be incorporated into the crystalline network of corals in the form of metal carbonates, associating themselves with the organic matter or by the deposition of terrigenous material. This work analyzes the concentrations of 4 metals related to environmental contamination (Cu, Zn, Pb and Ni) and Al as a normalizing element incorporated in 4 colonies from the Siderastrea stellata coral: two healthy and two bleached. Sediment samples adjacent to the corals were also analyzed (aluminum analysis was not determined for sediments). The determination of the Cu, Al, Pb, Zn, and Ni contents was obtained by flame atomic absorption spectrophotometry at the Biogeochemical Coastal Laboratory. The results obtained showed that the average concentration of metals in the healthy colonies was 2.8 µg.g-1 for Ni, 2.2 µg.g-1 for Cu, 4.8 µg.g-1 for Pb, 0.21 % for Al and 5.9 µg.g-1 for Zn. For the bleached colonies, we obtained 3.3 µg.g-1 for Ni, 2.05 µg.g-1 for Cu, 7.31 µg.g-1 for Pb, 0.04 % for Al and 6.61 µg.g-1 for Pb Zn. While the levels of metals obtained in the sediment samples referring to healthy colonies were 8.4 µg.g-1 for Ni; 3.4µg.g-1 for Cu; 11.7µg.g-1 for Pb; 12.3µg.g-1 for Zn. The significant difference in metal content in living and dead corals indicated that bleaching possibly alters the distribution of these metals in the organisms. However, there was no significant relationship between the origin and the distribution of the metals in the sediments and in the healthy and bleached colonies. The geochemical correlations with carbonate and organic matter were determined and discussed throughout the present study.