Abstract

Project Title – Parrotfish Grazing Rates Effect on Algal and Coral Abundance
Other Student Participants – Ingrid Hanson ’20, Alexis Shomon, Erin Magill ’20
Mentors – Craig Jackson, Amy Downing

This study’s purpose was to determine how parrotfish grazing affects the abundance of algal turf, bare rock, macroalgae, and coral in a reef community. In a coral reef algae and coral compete for space on hard substrates. Herbivores, such as parrotfish, are important in determining reef structure because they graze on the algae clearing more available hard substrate that may allow for coral to become more abundant. Here we quantify parrotfish grazing rates in different bays of Saint John in the U.S. Virgin Islands that span a gradient of algal turf, macroalgae, and coral abundance. Using one square meter plots, we observed  grazing by of parrotfish in the plot for three minutes and recorded all bites taken in the square meter over that period of time. We hypothesized that parrotfish would have higher grazing rates in areas of higher algal coverage (turf and macroalgae), and because of parrotfish grazing on the algae, relative abundance of coral would increase. We anticipated a negative correlation for parrotfish numbers and algal coverage, a positive correlation for parrotfish numbers and coral abundance, and a negative correlation between algal coverage and coral coverage. The results show that parrotfish grazing rates were higher in areas with high algal turf coverage because they prefer algal turf over any other item in their diet. This study allows us to better understand the crucial role herbivory plays in competition between algae and coral in a reef community and how herbivores could be helpful in assisting in coral recovery and abundance.