TRANSPLANTATION OF JUVENILE CORALS - A NEW APPROACH FOR ENHANCING COLONIZATION OF ARTIFICIAL REEFS

Coral reefs in the northern Gulf of Eilat are exposed to continuous ma n-made disturbances, resulting in decreased coral coverage and reduced recruitment at the Nature Reserve of Eilat. The construction of artif icial reefs on sandy bottoms is a possible option to decrease diving p ressure on natural reefs. In the present study we tested this hypothes is by submerging an experimental artificial reef anchored to the botto m at 18 m depth and floated vertically 3 m below water surface. The re ef was composed of PVC plates, attached both vertically and horizontal ly along a wire. Propagules of two coral species, the stony coral Styl ophora pistillata and the soft coral Dendronephthya hemprichi, were tr ansplanted to this artificial reef. Planulae of S. pistillata were obt ained during the breeding season, seeded in petri dishes in the labora tory and after 2 wk the dishes were transferred to the experimental ar tificial reef. Automized fragments of D. hemprichi which had previousl y settled on 10 x 10 cm PVC plates were transplanted onto the experime ntal artificial reef. The survivorship of the transplanted D. hemprich i colonies was significantly higher on the lower sides of shallower pl ates. Survivorship of S. pistillata colonies increased with depth when located on the vertical plates, or on the upper sides of the horizont al plates. The highest survivorship of this coral was on the vertical plates and on the upper sides of the horizontal plates, while very low survivorship was recorded on the lower sides. The results indicate th at vertical artificial surfaces offer the optimal biotic and abiotic c onditions for the survival of the two examined corals. The vertical pl ates are characterized by low sedimentation rates, low coverage of tur f-algae, minimal grazing by sea urchins and absence of the competitor tunicate Didemnum sp. In addition, the vertical orientation of the exp erimental plates reduces shading and offers the required light intensi ty for zooxanthellate corals such as S. pistillata. Only a few studies to date have tried to implement artificial reefs in a coral reef envi ronment. The results of the present study indicate the potential of en hancing recruitment of corals by transplantation of juvenile recruits onto appropriate artificial structures. Maximal survivorship of these recruits is dependent upon the structural features of the artificial r eef, which should offer optimal conditions.