Bleaching effect on regeneration and resource translocation in the coral Oculina patagonica

Bleaching of corals is the result of the loss of their symbiotic algae (zooxanthellae) and/or their pigments. The supply of photoassimilates provided by the zooxanthellae to the corals declines during bleaching and reduces their ability to activate energy-costly processes. In the present study we compared regeneration capabilities of unbleached Oculina patagonica colonies (an encrusting Mediterranean stony coral) with those of bleached and partly bleached colonies. Using the C-14 point-labelling technique on coral tissue, we examined possible intra-colonial translocation of photosynthetic products from the site of tissue labelling to recuperating lesions in partly bleached versus unbleached intact colonies, The percentage recovery of 2 cm 2 lesions inflicted on unbleached O. patagonica colonies was significantly higher than the percentage recovery of similar lesions within the bleached area of the partly bleached colonies. Totally bleached colonies showed no regeneration of lesions. Lesion regeneration in unbleached O. patagonica resulted in oriented intra-colonial translocation of C-14 products towards recuperating lesions located up to 4-5 cm away. In partly bleached colonies (40 to 80%), such translocation did not occur, probably explaining the reduced recovery rates of lesions in these colonies. Our findings suggest a bleaching threshold of ca. 30% within O. patagonica colonies that determines the levels of colony integration and intra-colonial translocation of resources to regions of maximal demand.