Macroalgal Production and Nutrient Relations in Oligotrophic Areas of Florida Bay
Abstract:Abundant macroalgae of southern Florida Bay were assayed for nitrogen (N) and phosphorus (P) limitation of productivity by enrichment effects on in situ growth rate, tissue C:N:P molar ratios, and capacity of alkaline phosphatase. Growth of two frondose rhodophytes, Gracilaria tikvahiae and Laurencia poitei, was stimulated primarily by P (although N was also limiting during winter) as was growth of two frondose phaeophytes, Sargassum polyceratium and Sargassum pteropleuron. Tissue C:P and N:P ratios of the unenriched rhodophytes were elevated, ranging from 1,080 to 1,939 and 75 to 147, respectively; C:P and N:P ratios of the unenriched phaeophytes were lower, ranging from 550 to 1,307 and 23 to 25, respectively. These tissue ratios support the primary P limitation suggested by the growth assays and suggest that phylogenetic differences may exist in storage and utilization of N and P compounds relative to C. Levels of dissolved inorganic nutrients (NH4 +, NO3 –, and PO4 3–) in seawater during these studies also suggest that P, relative to N, was most limiting during summer months when NO3 – and NH4 + were seasonally elevated and seawater N:P ratios were >30:1. Assays for alkaline phosphatase activity in phylogenetically diverse forms of Florida Bay macro algae indicated broadly different capacities of this exoenzyme, with the highest rates observed for Dictyota divaricata and L. poitei and the lowest rates for G. tikvahiae. Considering that D. divaricata and L. poitei had the greatest observed capacity for this enzyme and that these and related species are particularly abundant in southern Florida Bay, utilization of dissolved organic phosphate pools appears to be ecologically important to sustaining productivity of indigenous frondose macroalgae in P-limited Florida Bay.
Document Type: Research Article
Publication date: 1989-01-01
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