Estrutura populacional do Coral Mussismilia harttii (Verril, 1868) no Nordeste Brasileiro

Abstract

Coral reefs are unique ecosystems of great value for fishing activities, tourism and coastal protection around the world, however there are gaps on the conservation status of some populations. From the study of population structure, measured by the size of colonies and their polyps, it is possible to infer trends of population increase or decline and propose actions for management and conservation of species, especially those officially recognized as endangered. This study tested two hypotheses: (i) on a regional scale, the population of M. harttii in Northeastern Brazil has an "reverse J-shaped" population structure, possibly due to the proportionally greater historical human impact on large colonies; and (ii) on a local scale, the concentration of organic matter (sedimentation) from the continent reduces the size and abundance of colonies in subpopulations of M. harttii distributed in Northeastern Brazil. The study was developed in the states of Paraíba, Pernambuco, Alagoas and Bahia, totaling 15 subpopulations. The colonies were sampled in 2016 through the "reef-check" method (videotransect) and the concentration of organic matter through sediment sample collections. From each colony observed in the footage, their polyps were counted and measured with ImageJ software. In 12 subpopulations, a total of 31974 polyps were counted in 155 live colonies, with a mean of 206 and a median of 63 polyps per colony (2-3212 polyps per colony; minimummaximum). On average, polyps measured 1.64 cm in diameter (0.53-3.21 cm), with a coefficient of variation of 0.31 (0.02 to 1.17). As expected, the sampled population showed an "reverse J" pattern, characterized by the predominance of small colonies. There was a negative relationship between organic matter concentration and colony abundance, indicating that sites with a higher percentage of organic matter have fewer M. harttii colonies. Three subpopulations from highly visited tourist sites showed no colonies. However, there was no significant effect of organic matter on the size of polyps and their coefficient of variation. The results suggest that human activities impacting the coastal reefs of the Brazilian Northeast have removed mainly the larger colonies. Because these colonies have a higher reproductive potential, population decline is likely to intensify in the coming years unless conservation and management measures are taken.