Storms may disrupt top-down control of algal turf on fringing reefs

Abstract

Storms strongly affect coral reefs; one unstudied but potentially important outcome may be a decrease in herbivory, presumably through changes to freshwater, sediment and nutrient influx. Algal turfs are sensitive early indicators of reef condition, and experimental evidence demonstrates low sediment loads and strong herbivory maintain short, healthy turf. While unknown, storms likely disrupt these controlling forces. We have observed storms that generate frequent, visible sediment plumes in Moorea, French Polynesia. To evaluate the effects of storms on herbivory, we conducted a set of field experiments manipulating herbivore access to naturally occurring turf under three rainfall regimes: no rain, light rain, and heavy rain that generated a plume event. We found strong effects of herbivores except following the storm, indicating disruption of typically strong top-down control by herbivores on algal turfs. Further research into the underlying mechanisms is critical as storm intensities and watershed development increase in many tropical regions.