Sedimentation and distributions of green and brown morphs of the Caribbean coral Porites astreoides Lamarck

Sediments suspended in the water column and settling on to reef surfaces are thought to exert control on coral distributions through both lethal and sublethal effects. I investigated whether variation in sedimentation rates can adequately explain patterns of distribution observed along depth gradients for green and brown colonies of the common Caribbean coral Porites astreoides Lamarck. Colony abundances and rates of downward flux of suspended particulates (i.e., sedimentation rates) were assessed along depth gradients at four sites (Tague Bay, Buck Island, Cane Bay and Salt River Canyon) on St. Croix, US Virgin Islands. In all but one instance, 12 m depth at Tague Bay, distributions of green and brown P. astreoides varied predictably with differences in sedimentation rates: higher levels of sedimentation corresponded with a lower proportion of green colonies. Laboratory experiments conducted with colonies from the low sediment Cane Bay site showed that brown colonies not only shed sediment from the colony surface significantly better than green colonies, but also suffer less sediment-induced tissue death. While previous models of sediment resistance in corals have been based on variation in colony shape and polyp architecture, results obtained here indicate that major differences in these parameters may not be necessary for differential tolerances to occur. (C) 1998 Elsevier Science B.V. All rights reserved.