Seriatopora are abundant reef-building, or hermatypic, corals and harbour symbiotic algae (zooxanthellae) within their tissues. Zooxanthellae provide the coral with nutrients, obtained via photosynthesis (5). One of the most curious methods of asexual reproduction in corals was discovered in a Seriatopora coral when polyps were observed detaching themselves from a dying colony. The skeleton-less polyps were then able to form new colonies by normal budding. This phenomenon, termed ‘polyp bail-out’, is a unique escape response to environmental stress, and may also be considered a form of asexual reproduction (6). Seriatopora corals can also reproduce asexually by fragmentation, and sexually by brooding, in which larvae develops inside the polyps, and mature larvae is then released into the water column where it will disperse, eventually settling on the substrate and establishing a new colony (5).
Parts of Seriatopora colonies sometimes show remarkable modifications caused by other organisms, most notably the gall-forming crab Haplocarcinus marsupialis. Female crabs of this species influence the growing tips of coral to form a ‘gall’ which is effectively a cage that permanently encloses the crab, (like a pair of cupped hands). Male crabs, which are much smaller than females, are able to enter the coral cage to mate. The female spends her whole life in this self-imposed captivity producing broods of larvae inside the protective walls of her cage (3).