Phase-shift in coral reef communities in the Florida Keys National Marine Sanctuary (FKNMS), USA |
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Authors: | Ronald J Maliao Ralph G Turingan Junda Lin |
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Institution: | (1) Department of Biological Sciences, Florida Institute of Technology, 150 West University Blvd., Melbourne, FL 32901-6975, USA |
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Abstract: | Characterizing the Florida Keys National Marine Sanctuary (FKNMS), USA, has gained much attention over the past several decades
because of apparent changes in the benthic community structure over space and time representative of patterns occurring in
the Caribbean region. We used a 5-year dataset (1996–2000) of macroalgal and sponge cover and water quality measurements as
predictor variables of hard coral community structure in the FKNMS. The 16 water quality variables were summarized into 4
groups by principal component analysis (PCA). Hierarchical agglomerative cluster analysis of the mean and standard deviation
(SD) of the principal component scores of water quality variables separated the reef sites into two main groups (and five
sub-groups), referred to as reefs of similar influence (RSI). The main groups corresponded with their geographical locations
within the Florida Keys: the reefs in the Upper and Middle Keys being homogeneous and collectively, having lower water quality
scores relative to reefs in the Lower Keys. Canonical correspondence analysis (CCA) between hard coral cover and key predictor
variables (i.e., water quality, macroalgal cover and sponge cover) also separated the reefs in the Lower Keys from reefs in
the Upper–Middle Keys, consistent with results of the cluster analysis, which categorized reefs based on RSI. These results
suggest that the prevailing gradient of predictor variables may have influenced the structuring of coral reef communities
at a spatial scale larger than the individual reef. Furthermore, it is conceivable that these predictor variables exerted
influence for a long time rather than being a recent event. Results also revealed a pattern showing reduction in hard coral
cover and species richness, and subsequent proliferation of macroalgae and sponges during the study period. Our analyses of
the Florida Keys present a pattern that is consistent with the characteristics of a reef that has undergone a “phase-shift,”
a phenomenon that is widely reported in the Caribbean region. |
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