HCNSO Student Theses and Dissertations

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Defense Date

8-2013

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

David S. Gilliam

Second Advisor

Brian K. Walker

Third Advisor

Kathleen S. Lunz

Abstract

The widespread decline of Acroporid corals throughout the Western Atlantic and Caribbean has been well documented over the last several decades. Acropora cervicornis and Acropora palmata were listed as threatened on the US Endangered Species Act in May of 2006. Major contributors to Acropora species mortality include disease, predation, sedimentation, nutrient loading, thermal stress and storm damage. These stressors, combined with the species dependence on asexual reproduction and limited potential for larval recruitment, make the full recovery of populations uncertain.

Several Acropora cervicornis patches have been documented offshore southeast Florida, despite the substantial impact of both natural and anthropogenic disturbances nearshore Broward County, FL. Some investigation has been done on the distribution, abundance and ecological structure of some of these patches, but limited information exists on abundance and distribution outside of these dense patch boundaries. Acquiring such data requires thorough investigations throughout the near-shore habitat of southeast Florida. The first goal of this study was to investigate the current Acropora cervicornis distribution in this near-shore habitat to utilizing a recent large-scale data set and determine if they are spatially uniform or clustered. The second goal was to investigate the effects of key habitat characteristics on locations of high densities of A. cervicornis, in the form of large-scale topographic metrics through the use of GIS and high resolution bathymetry data. The third goal was to compare several characteristics of colonies and fragments inhabiting the near-shore habitats over the course of a year to investigate the existence of any habitat specialization. These characteristics included size, mortality, condition (presence of recent mortality due to disease or predation), morphology, attachment success and persistence.

The Getis-Ord Gi* statistic and Anselin Local Moran’s I spatial cluster analysis of abundance showed significant clustering at several locations within the research area which was supported by the inverse distance weighted surface model (IDW). Topographic metrics with a significant influence in predicting Acropora cervicornis presence were substrate type, proximity to shore and to a ridge. There were no significant differences in colony size, percent mortality or condition between colonies on pavement and rubble. Probability for colony sustainability was significantly greater on pavement than rubble. There was no significant difference in branching angles or diameters on colonies inhabiting rubble or pavement. However, colonies growing in rubble had significantly more branching than colonies growing on pavement. Several significant differences between the measures of plot composition (abundances of attached colonies, loose fragments and incidences of disease and predation within a defined area) between pavement and rubble were observed. There were more colonies and loose fragments on rubble sites than pavement sites throughout the duration of the study. There were significantly higher percentages of diseased masses on rubble than on pavement. Significant differences were found in 3-dimensionality and attachment success of fragments between those monitored on pavement and rubble. Fragment movement was not significantly different between substrates.

This research supports NOAA’s designation of the southeast Florida near-shore environment as critical habitat for Acropora cervicornis. Acropora cervicornis is a sessile invertebrate, but its life history strategies allow for considerable mobility. This study showed that A. cervicornis inhabits the whole depth range and all substrates present within the near-shore study area. Protective seafloor topography is likely to influence where aggregations are found but the appropriate combination of factors to predict where these locations are, has yet to be determined. Limited evidence of habitat specialization by means of substrate was observed but more needs to be acquired to confidently claim it is occurring. Acropora cervicornis displays similar growth, mortality and condition characteristics on both pavement and rubble; however observed differences in morphology may hold the key to understanding where sexual reproduction is most successful. More information on the morphological responses of A. cervicornis to various forms of injury is required.

The results of this research enables proactive management for conservation of the threatened coral, Acropora cervicornis, through the production of a distribution map, better understanding of local habitat associations, and providing a baseline for future monitoring and research on population dynamics.

Comments

Funding provided by Broward County.

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