Assessing the expression of different biochemical indicators in scleractinian corals subjected to biotic and abiotic stresses.

In the last few decades about the 27% of coral reefs have been destroyed worldwide caused by different environmental stressors, both abiotic and biotic. Moreover one of the main causes of coral reef destruction has been the dramatic increase in coral disease. In reef building corals, as well as in other organisms, several components of the cellular stress response can be used as diagnostic indicators of stress, in order to assess their cellular physiological condition, expressing them with significant different patterns in relation to different stressors. In this study the diagnostic indicators used were: Heat shock protein 60-kDa (Hsp60), Heat shock protein 70-kDa (Hsp70), Heme-oxygenase (HO-1), and Manganese Superoxide Dismutase (MnSod), all involved in cellular response to stress. Two of the most studied diseases responsible for ongoing coral losses on Indo-Pacific reefs were chosen as the biotic stressors: the Brown Band Disease (BrB) and Black Band Disease (BBD). BrB is a virulent coral disease characterized by a dense concentration of ciliates ingesting coral tissue. In order to investigate the effect of the ciliate presence in the coral physiology, the level of the mitochondrial Hsp60 was analyzed in colonies of Acropora muricata affected by BrB in a Maldivian reef. Samples in the apparently healthy coral polyps located at different distances along the advancing front of the infection were analyzed. The BBD is characterized by a thick microbial mat, dominated by phototrophic cyanobacteria, which is responsible of the disease virulence and create the characteristic necrotic dark band. It is known to be persistent in reef, contributing to the long term mortality of the infected coral. In Maldives waters one of the highest prevalence was observed in Goniopora columna, which show a very slow progression rate. Due to its high persistence in infected corals, colonies of Goniopora were analyzed in two time periods, space out by three years. Samples in the apparently healthy coral polyps were collected at three different fixed distances along the advancing front of the infection from the black band of necrotic tissue, in order to analyze how the disease’s progression affect the expression of Hsp60 and Hsp70, HO-1, and MnSod. Finally Hsp60, Hsp70 and HO-1 were analyzed in relation to nictemeral and seasonal variations of temperature and light, in three different taxa of reef building corals living in the Maldivian waters: Acropora, Echinopora and Porites. These three taxa were chosen for their different growing morphology and susceptibility to stress. Samples were taken in November for the wet season and March for the dry season in order to made a comparison between the two seasons. During each selected month, in a day, corals were sampled in six time intervals while temperature and light intensity were measured by data-loggers attached to the colonies. Results show the biochemical indicators used being modulate in different ways in relation to species and stressors.