Utilisation de la croissance de transplants du Scléractiniaire hermatypique Acropora muricata (Linnaeus, 1758) comme bioindicateur (île de La Réunion, océan Indien)

Abstract

Searching for bioindicators easy to use but integrating the influence of environmental factors, in order to help understanding the functioning of different sites on a reef flat, we chose to study the growth of transplants of the hermatypic Scleractinian Acropora muricata. We asked if the growth of transplants of this sensitive coral could constitute an interesting bioindicator. Are rapid and simple measures of the growth of the transplants, over a relatively short period (between 6 months and 1 year), able to express significant differences among different biotopes ? In our study, after one year, the growth of transplants results in a slender and open form on a dystrophic reef flat, in a balanced form in an oligotrophic reef flat non subject to a high level of predation, and in a stocky form showing numerous points of adaptative reiteration due to traumatisms on a reef flat subject to a strong swell and a high level of predation. The easy observation of the transplants allows to demonstrate the pressure of predation on living coral colonies, a phenomenon difficult to observe on large branching colonies. The bioerosion which is fundamentally opposed to calcification appears to be, in the case of the external macroerosion by the fish Scaridae, a phenomenon that could secondarily stimulate the calcification. We estimate that the growth of transplants of Acropora muricata can constitute a good bioindicator of the effects of abiotic and biotic factors on sensitive Scleractininians.