Adult colonies of the reef-building coral St lophora pistillata discriminate precisely between ' self ' and ' nonself ' attributes, and respond selectively against specific allogeneic challenges. We studied the ontogeny of these allospecific responses on newly settled polyps by establishing allogeneic contacts within groups of 2-6 siblings or non-related offspring. Interactions were observed for up to 8 months. Three types of response, depending on the age of the interacting partners, were documented. The first was tissue fusion and the formation of a stable chimera, observed in partners less than 2 months old. The second was observed in contacts of partners 2-4 months old. It started with tissue fusion and transitory chimera since separation of the chimera partners or polyp death resulted when the oldest partner in the chimera reached the age of 4 months. The third type was the regular histoincompatibility response, as documented in allogeneic interactions of adult colonies, recorded here in all encounters with S. pistillata partners over 4 months old. Maturation of allorecognition in this species was therefore achieved through three time-dependent stages, 4 months following metamorphosis. Combinations of siblings or genetically unrelated partners did not affect the results. We propose that the coral alloimmune maturation system may be used as a new evolutionary model scheme for studying tissue transplantation and tolerance.

ABSTRACT. Here cve document for the first tlme an oriented intra-colonial translocation of photosynthetic products to~rards regenerating areas in 2 scleractinian corals, Favia favus (n = 5 ) and Platygyra lamelljna (n = 3) in Eilat (Red Sea). I4C bicarbonate was injected into round stainless-steel cylinders (10 h daylight incubation period) enabling labeling of a restr~cted tissue area of 20 cm2 in each colony center. Three tissue lesion sizes (small, intermediate and large) were inflicted simultaneously on each colony at a distance of 10 cm from and at different angles to the labeled area. After 3 wk, tissue and skeletal samples were taken from various locations on the coral colonies, and ''C activity was determined. In F. favus a significant labeling of tissues was recorded In areas bordenng the recuperating large lesions and along the axis connecting these lesions with the labeled centers. This pattern of labeling was not found in the smaller les~ons. In P. lamelljna I4C incorporation was recorded In the tlssues bordering large as well as intermediate sized lesions. The skeletal samples from F. favus showed significant 'v deposition in areas bordering the large lesions, indicating the use of translocated I4C materials for skeletogenesis in large lesion regeneration. Our results indicate that I4C labeled materials originating in distant areas of the coral colony are translocated towards large regenerating les~ons. Furthermore, the size of the coral lesion is shown to affect the magnitude of this translocation.

The present study examined the effect of lesion size and shape on the recovery rates of the scleractinian colonial coral Favia farms Five tissue lesion types, differing in surface area and perimeter, were artificially Inflicted on the upper surface of 46 F. favus colonies in the shallow reef across from the Marlne Biology Laboratory of Eilat (Red Sea). The gradual closure of these lesions was monitored monthly from January to March 1995 by underwater photography. Photographs over time were analyzed with a computerized image analyzer, enabling accurate measurements of the emerging tissue. In this study we present the percent recovery of the various lesion types through time and the ratios between the newly formed tissue and the penmeter length (NFT/P) of each specific lesion. These results show for the first time the significant effect of lesion size and shape on the regeneration capability of a colonial coral. We found that the high recovery rates achieved during the first month are regulated mainly by the penmeter length of the lesion, while during the following months recovery IS influenced more by the surface area of the les~on and its surface area/perimeter ratio. The vanous NFT/P ratios recorded in this study indicate that lesions with a relatively long perimeter probably obtain a h~g h e r energetic allocation from the colony, probably due to the larger colony portion associated w~t h their recovery.

Convergence of form and function has accompanied the evolution of modular growth in terrestrial plants and colonial marine invertebrates. Part of this convergence is related to the optimal exploitation of resources (space and light) and the ability to translocate energy products from sources to sink sites. Feeding on the energy pathways and energy sinks of terrestrial plants is a well-known phenomenon. Hermatypic corals, the major organisms constructing tropical reef environments, contain photosynthetic algae (zooxanthellae), energetic products of which are translocated towards sink sites located at the corals' growing tips and regenerating areas. Despite the plant^coral convergence in energy pathways and sinks, there has been no evidence to date that coral energy sinks are exploited by coral predators. Gastropods of the genus Coralliophila are found feeding on coral margins, causing small and localized tissue damage. However, the ability of these snails to continue to feed without moving over a long period remains puzzling. Using a 14 C labelling technique, we found that colony margins of the stony coral Porites function as major energy sinks. When snails inhabited these sites they incorporated signi¢cant amounts of 14 C, indicating that they had fed on photosynthetic products translocated from the interior of the colony. Furthermore, when snails aggregate in the interior of the colony, thereby causing large surface injuries, they induce the development of signi¢cant new sink sites. This mode of prudent sessile feeding maximizes the e¤ciency of energy exploitation by the predatory snail, while minimizing tissue damage to the coral. The fact that energy sink sites occur in many coral species suggests that the strategy of sink exploitation for nutrition could also occur in many other marine host^symbiont relationships.

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 14 C 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 14 C 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.