PS 48-12 - Palatability of seagrass species in Brewers Bay, St. Thomas, USVI

Thursday, August 10, 2017
Exhibit Hall, Oregon Convention Center
John S. Cassell, Center of Marine and Environmental Science, University of the Virgin Islands, St. Thomas, Virgin Islands (U.S.), Edwin Cruz-Rivera, Department of Biological Sciences, University of the Virgin Islands, St. Thomas, Virgin Islands (U.S.), Paul Jobsis, Center for Marine and Environmental Science, University of the Virgin Islands, St. Thomas, Virgin Islands (U.S.) and Sandy Wyllie-Echeverria, University of the Virgin Islands, St. Thomas, Virgin Islands (U.S.)

Recently a seagrass originating from the Red Sea, Halophila stipulacea, has expanded into the United States Virgin Islands (USVI). Currently on St. Thomas there are multiple bays where H. stipulacea competes for space with native seagrasses. There are concerns about its impact to the feeding behavior of local herbivores but few studies exist. Furthermore, no publications have been made thus far regarding the nutrient content of this plant in the Caribbean, which is necessary to help scientists understand how animals will perceive it as a food source. This project is the first to examine the nutritional quality and palatability of seagrasses found in Brewers Bay through chemical analyses, observational surveys, and choice-feeding experimentation. We collected H. stipulacea and two native seagrasses, Thalassia testudinum and Syringodium filiforme, every four months between 2016 and 2017 to compare nutrient contents seasonally. In addition, weekly snorkel surveys in the bay were conducted for six months to count how many green sea turtles, Chelonia mydas, were present and whether they grazed within monotypic or mixed stands of seagrass. Finally, we utilized mesocosms located at the univeristy to conduct multiple choice feeding experiments to determine the preference of long-spine urchins, Diadema antillarum.


Currently, seagrass samples have been shipped to collaborators at Washington State University for nutrient examinaton. The sea turtle surveys revealed patterns of impartial behavior towards H. stipulacea. 41.7% of all turtles counted grazed within native patches and 44.4% were spotted in mixed patches. An unpaired T-test proved nonsignificance between grazing categories (p=0.965). However, when offered seagrass in a mesocosm, D. antillarum showed preference to S. filiforme. A non-parametric Friedman’s Test reinforced the significance (p=0.008) of this preference.

What our project can conclude without knowing nutrient content is that large herbivores like C. mydas will consume H. stipulacea with little hesitation potentially because of the daily weights required for their diet. But for small species like D. antillarum chemical defenses or poor nutrient quality may play a greater role in food selection. Overall, our methods and findings will be critical for natural resource managers and researchers on other Caribbean islands invaded by this seagrass.