HCNSO Student Theses and Dissertations

Defense Date


Document Type


Degree Name

M.S. Marine Biology


Oceanographic Center

First Advisor

Brian E. Lapointe

Second Advisor

Richard E. Dodge

Third Advisor

Curtis Burney


Anthropogenic nutrient enrichment and coastal eutrophication are a primary threat to the biological integrity of coral reef ecosystems. Macroalgal blooms are one symptom of eutrophication and provide useful 'bioindicators' of the nutrient dynamics associated with the eutrophication process. This study used marine macroalgae to monitor physiological processes associated with eutrophication by comparing the degree of phosphorus (P) limitation in reef and nearshore environments of the highly developed Florida Keys with the relatively pristine Bahamas by measuring enzymatic alkaline phosphatase activity (APA), tissue composition, and water column nutrient concentrations [total nitrogen (TN) and total phosphorus (TP)]. Experimental nutrient enrichment studies were also performed to help interpret the field data from the Florida Keys and the Bahamas. Despite their large spatial scale and habitat heterogeneity between the Florida Keys and the Bahamas, and the inherent biological variability among the numerous taxa assayed, highly significant and distinct differences in macroalgae between the two study areas were evident. The analysis showed macroalgal APA was 2.5-fold higher in reef environments and 1.5-fold higher in nearshore environments in the Florida Keys than the Bahamas, indicating higher P-limitation in the Florida Keys. This was related to the significantly higher water column TN concentrations within the Florida Keys. Additionally, a significant and positively correlated relationship was detected between macro algal APA and tissue N:P ratios, indicating that elevated water column N causes the N:P ratio of macro algae to increase, leading to the observed increase in P-limitation. These findings showed that marine macroalgae are a useful means to monitor and gauge the degree and type of nutrient limitation and that N inputs as well as P inputs need to be considered for the protection of water quality in carbonate-rich, coral reef regions.

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