Potential new avenues for expediting recovery of long-dead Acropora palmata skeletons.

Abstract:

Acropora palmata effectively disappeared from the Caribbean and Western Atlantic following the 1970 – 1980’s white band epizootic and subsequent, frequent bleaching events. Recovery has been minimal in most regions due to the drastic reduction and isolation of fecund colonies and the resultant allee effect; neither sexual reproduction nor fragmentation has pushed recovery towards a positive trajectory. This study seeks to assess the current state of A. palmata in Little Cayman by a complete inventorying of a 200m stretch of the shore-parallel reef of Grape Tree Bay and investigate what can be done to expedite recovery. The current population was assessed by GIS-locating 496 colonies and recording live cover, evidence of re-sheeting, morphology, and presence/absence of grazers and dominant macroalgae. Long-dead colonies were categorized as either fused acropora rubble, erect remnant (no branches), or long dead Acropora palmata (with branches). The ability of partially live colonies to fully recover will be assessed by re-visiting 25 colonies that had stainless steel screws cemented at the live tissue/macroalgae margin. Similarly, potential enhancement of recruitment will also be assessed by re-visiting 15 long-dead colonies that were scrubbed to bare skeleton. The distribution of colonies, particularly live small colonies, was found to be strongly dependent on substrate. A strong preference was found for fused rubble and and a special type of fused Acroporid rubble that presumably lithified during the last glacial low-stand. There was strong evidence of recent sexual recruitment, contrary to the largely-accepted assumption of fragmentation as the primary mode of reproduction.