The Interactive Role of Inorganic and Organic Nutrients in

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					 The Interactive Role of Inorganic and Organic Nutrients in
Controlling Coral Health and Bioeroding Algal Communities

 Diana Pietri, Department of Evolution, Ecology, and Environmental
 Biology, Columbia University

 Research Mentor: Tim McClanahan,
 Research Advisor: Bill Hahn,

        In recent years, many Caribbean coral reefs have shown a substantial decline in coral

health, demonstrated by coral bleaching and the overgrowth of macroalgae. The latter often

occurs after the coral is weakened by other disturbances, and once algae overtake the coral,

recovery is difficult. Increase in organic and inorganic nutrient concentration of the water is

thought to be the main cause of the increased algal growth. In this study, coral plates and

colonies of Porites porites and Diploria labrynthiformes were treated with organic (sawdust) and

inorganic (nitrate/phosphate fertilizer) nutrients in order to see the effects of the nutrients on the

coral and algal growth. The results indicate that increased nutrients did cause an increase in

algal growth (both cover and weight) and also caused darkening of the coral colonies. Organic

matter caused a smaller increase in algal growth, and it caused bleaching of the Diploria

labrynthiformes colonies. Organic matter also significantly influenced herbivory. Statistical

analyses of these results demonstrated that the combination of organic matter and inorganic

nutrients has the most significant effect on algal growth and coral health. The results of this

study can be used to help understand some of the potential causes of increased algal growth on

coral reefs.

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