Fragmentation in Madracis mirabilis (Duchassaing and Michelotti):: How common is size-specific fragment survivorship in corals?

Fragmentation is an important asexual mode of reproduction for many coral species and other marine invertebrates. General life history theory and models of coral fragmentation predict that intra- and inter-specific variation in fragment size should be positively related to survival and inversely related to dispersal distance. To test these predictions I examined fragmentation in the Caribbean branching coral Madracis mirabilis, which produces relatively small fragments. The effects of intra-specific variation in fragment size on fragment survival and dispersal in M. mirabilis were examined by following the fate of 60 labeled fragments for 11 months at three sites. Fragment dispersal distance was limited (generally < 20 cm), was not significantly related to fragment size, and varied among sites, being greatest at a shallow forereef site. Although the smallest fragments displayed the lowest survivorship (approximate to 50%), there was no apparent increase in survivorship with size among larger fragments (i.e., those 5-15 cm in length), and there was no overall significant relationship between fragment size and survivorship. In contrast, fragment survivorship varied greatly among sites (29-81%), being the highest at two forereef sites (10 and 20 m depth) and lowest at a lagoon site with high sedimentation (10 m depth). Although natural fragments of M. mirabilis are smaller than almost any other known fragmenting coral species, they can have a high rate of survivorship in forereef environments. The results of this and other studies do not support the predicted general inter- and intra-specific relationships between fragment size and survivorship and suggest that fragment survivorship is highly context and species specific, and is also greatly influenced by factors other than fragment size. (C) 1998 Elsevier Science B.V. All rights reserved.