Structural deformation of branching corals associated with the vermetid gastropod Dendropoma maxima

The vermetid gastropod Dendropoma maxima is found in association with diverse coral species. This association is often characterized by the coral head covered by a wide mucus net secreted by the gastropod to trap food particles from the water column. Here we report on the quantitative effect of the gastropod on the morphology of Stylophora pistillata, one of the most abundant branching corals on the reef flat in Eilat (Gulf of Aqaba/Eilat, Red Sea). The existence of D. maxima in the vicinity of corals plays a significant role in deforming coral morphology. Compared with corals located outside the influence range of D. maxima, affected corals were found to be approx. 52% lower in their vertical dimension and approx. 35% smaller in diameter, and their slenderness ratio (height:diameter ratio) was found to be approx. 35% smaller. In addition, we found that over the last decade the population of D. maxima on the reef flat in Eilat has significantly increased in density (by a factor of approx. 2.5). The reason for this dramatic increase is currently unknown. However, it may be linked to the reported eutrophication of the northern Gulf of Aqaba, as this kind of environmental shift enhances the competitive advantage of suspension feeders over corals. Thus, the increase in the gastropod abundance may be a precursor of change in the reef flat community structure.