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The first scleractinians, progenitors of modern corals, began to appear 240 million years ago; by the late Jurassic (150 Ma) most families of modern corals had evolved and begun forming reefs (1, 2). Mechanisms controlling the recruitment of new corals to sustain these structures are, however, poorly understood (3). Corals, like many marine invertebrates, begin life as soft-bodied larvae that are dispersed in the plankton (3, 4). As the first step in developing a calcified coral colony, the larva must settle out of the plankton onto a suitable substratum and metamorphose to the single calcified polyp stage cemented to the reef (3, 5). Our analyses of the metamorphic requirements of larvae in divergent coral families surprised us by revealing the existence of a common chemosensory mechanism that is required to bring larvae out of the plankton and onto the reef. This mechanism appears to be quite old, predating both the phylogenetic divergence of these coral families and the development of different modes of coral reproduction.

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