Date of Award

8-2007

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Robert S. Steneck

Second Committee Member

Susan H. Brawley

Third Committee Member

James M. Acheson

Abstract

Larval recruitment is a leading driver of community structure in the marine realm. Recovery of community assembly following an acute disturbance should occur predictably at the process level. However, coral reefs worldwide are suffering from increasing rates of disturbances from bleaching, disease, and algal overgrowth and many show little to no sign of recovery. While we know much about what causes coral reefs and other ecosystems to collapse, we know relatively little about what contributes to their recovery. We sought to determine if critical sequential phases in settlement and post settlement processes control coral recruitment on the reefs of Bonaire (Netherlands Antilles) where coral abundance is high and algal abundance is low relative to other Caribbean coral reefs. To manipulate algal biomass surrounding potential coral nursery habitats, we placed standardized terra-cotta coral settlement plates inside and outside of damselfish territories and wire cages. We found local turf algal cover may impede larvae from accessing the benthos, and after 27 months, spat densities were 73% higher in well- grazed treatments. Spat settled preferentially on crustose coralline algae, biofilms, and calcareous polychaete worm tubes, suggesting demographic importance of facilitator substrates. Our study suggests there may be a dynamic balance between the positive effects of settlement facilitators and the negative effects of turf algal abundance and other settlement inhibitors that limit coral settlement and survival. Elevated abundance of turf algae within centimeters of possible settlement habitats decreased the recruitment potential of reefs by impeding larval access to settlement habitats and decreasing post-settlement survivorship. Thus, this dynamic interaction affects recruitment at several points during and immediately following larval settlement. This illustrates the "gauntlet" of sequential processes through which corals must pass to recruit to coral reefs. With the highest proportion of surviving coral spat successfully running the gauntlet under conditions of relatively low turf algal biomass, this study suggests that herbivory, or a lack thereof, explains a considerable portion of the variance associated with coral recruitment at a very local scale. Thus, careful management and monitoring of herbivores could improve the potential for coral reefs to recover from disturbances.

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