Episodic Nutrient Supply to Pelagic Sargassum in Neritic Versus Oceanic Waters

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The productivity of pelagic Sargassum may not be nutrient limited at those times when the macroalga drifts into neritic waters. Preliminary observations suggest that episodic enrichment resulting from associated fish schools may account for a large fraction of nutrient availability to Sargassum in neritic waters. This work will: 1) Quantify the abundance of fish schools and their relative importance as a nutrient source to Sargassum in neritic versus oceanic waters. 2) Characterize the organic nutrient pools associated with dissolved excretion and defecation by fish schools. 3) Characterize short term physiological and biochemical responses of Sargassum to N and P enrichment typical of that resulting from fish excretion and defecation. These studies will determine for the first time the potential importance of fish excretion to nutrient supply of a macroalgal community. Typically, plant growth in offshore waters is dominated by microscopic plants suspended in the surface sunlit layer. However, a floating seaweed called Sargassum is common throughout the area off the southeast coast of the United States. In the proposed work, Lapointe seeks to answer questions regarding the large scale (basin) distribution of this unusual plankton form. He will examine the hypothesis that the circulation of Sargassum through nearshore water is a critical stage during which nutrients from schooling fish relieve the nutrient depleted conditions that the plants encounter in more offshore waters. This is a unique "ecophysiological" approach that blends research in the biology of macroalgae with research in large scale oceanographic conditions. Dr. Lapointe is a recognized expert in the nutrition of seaweeds and this work will help clarify the plant production ecology of Atlantic subtropical regions.