Production of phenolics by seagrasses: patterns and ecological significance

A change in the production of chemical deterrents by a plant following herbivory that reduces future incidences of grazing is referred to as inducible resistance. Most of our current knowledge of inducible resistance comes from terrestrial ecosystems, and the few studies of inducible resistance in marine systems use macroalgae as their plant model. Phenolic compounds are a class of phytochemicals often involved in inducible resistance in terrestrial plants and macroalgae, and their production is thought to be metabolically costly to these plants. These compounds are found in seagrasses, but their role is not understood. Seagrasses are marine vascular plants that provide habitat for ecologically and economically important fish and invertebrate species. Seagrasses are in decline worldwide, and many researchers attribute this to increases in nutrient loading in coastal areas. Among other effects, increased nutrients can change the rate of production of phenolic compounds in seagrasses, although the specific effects of nutrient levels on seagrass phenolic production are unclear. Though they are in decline, seagrasses persist in areas of high grazing pressure and are known to possess the most common class of inducible chemical deterrents, which makes them excellent candidates for the study of inducible resistance. Here, I propose a study that will expand our understanding of the role of inducible resistance in seagrass systems. This study will determine if production of phenolic compounds is induced in two seagrasses (Thalassia testudinum and Halodule wrightii) by grazing by three grazers (a sea urchin, a limpet, and an amphipod). It will also determine if production of phenolics by these seagrasses is costly to the plants and how nutrient additions affect production of phenolics by these seagrasses.