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The Effects of Long-Term Manipulation of Nutrient Supply on Competition between the Seagrasses Thalassia testudinum and Halodule wrightii in Florida Bay

James W. Fourqurean, George V. N. Powell, W. Judson Kenworthy and Joseph C. Zieman
Oikos
Vol. 72, No. 3 (Apr., 1995), pp. 349-358
Published by: Wiley on behalf of Nordic Society Oikos
DOI: 10.2307/3546120
Stable URL: http://www.jstor.org/stable/3546120
Page Count: 10
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The Effects of Long-Term Manipulation of Nutrient Supply on Competition between the Seagrasses Thalassia testudinum and Halodule wrightii in Florida Bay
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Abstract

Long term (8 yr) continuous fertilization (via application of bird feces) of established seagrass beds in Florida Bay, FL, USA caused a change in the dominant seagrass species. Before fertilization, the seagrass beds were a Thalassia testudinum monoculture; after 8 yr of fertilization the seagrass Halodule wrightii made up 97% of the aboveground biomass. Fertilization had a positive effect on the standing crop of T. testudinum for the first two years of the experiment. The transition from T. testudinum-dominated to H. wrightii-dominated was dependent on the timing of colonization of the sites by H. wrightii; the decrease in T. testudinum standing crop and density at the fertilized sites occurred only after the colonization of the sites by H. wrightii. There were no trends in the standing crop or density of T. testudinum at control sites, and none of the control sites were colonized by H. wrightii. The effects of fertilization on these seagrass beds persisted at least 8 yr after the cessation of nutrient addition, suggesting that these systems retain and recycle acquired nutrients efficiently. Results of these experiments suggest that Halodule wrightii, the normal early-successional seagrass during secondary succession in Caribbean seagrass communities, has a higher nutrient demand than Thalassia testudinum, the normal late successional species, and that the replacement of H. wrightii by T. testudinum during secondary succession is due to the ability of T. testudinum to draw nutrient availability below the requirements of H. wrightii.

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