EFFECTS OF A HURRICANE ON SURVIVAL AND ORIENTATION OF LARGE ERECT CORAL-REEF SPONGES

In October 1988, Hurricane Joan struck reefs in the San Bias Islands, Panama, where hurricanes had never been recorded. Effects on large erect sponges were dramatic. For several years before the hurricane, the three most common sponges had been studied, providing pre-storm data on population structure and dynamics. Nearly half the individuals and biomass of three species were lost in the storm. The species were not affected in the same way, even though they are all of erect branching growth forms. Iotrochota birotulata lost significantly more individuals than Amphimedon rubens (57.6% vs 42.9%), which lost significantly more individuals than Aplysina fulva (31.6%). Patterns of biomass loss were very different, with both Iotrochota and Aplysina suffering losses of about 50%, but Amphimedon losing only 4.9%. Patterns of loss appear to be related to differences between species in the relative proportions of spicules (siliceous) and spongin (protein) in skeletal fibers and by differences in the speed and success rate of fragment reattachment. The incidence of toppling due to base failure varied among the six most common large erect sponge species, with significantly less toppling of the two species with skeletons composed solely of spongin. Clones of Iotrochota birotulata characterized by narrow branches suffered disproportionately greater losses than clones with more robust branches. The abundance of very small sponges, possibly developed from sexually produced larvae, was an order of magnitude higher after the storm than before.