Abstract
Parrotfishes are important reef herbivores helping to reduce algae and maintain coral cover, which is especially critical as coral reefs face disease outbreaks, climate change, and anthropogenic disturbances. Previous studies have shown that different parrotfish sizes and species affect the functional role these fish have on algal communities. Parrotfishes are not targeted by Florida fisheries and face little fishing pressure. In the US Virgin Islands, parrotfishes are targeted, likely causing a difference in the parrotfishes’ community dynamics between Florida and USVI. This project investigates the relationship between parrotfishes and algae in each reef system using data collected by the National Coral Reef Monitoring Program reef visual census point count and line point intercept methods. Parrotfishes densities and macroalgae percent cover were calculated for multiple years in the Florida Keys, Dry Tortugas, Southeast Florida, and St. Croix, St. Thomas and St. John, USVI. Evidence was found for bottom-up control of the densitiesof certain parrotfish species by their preferred macroalgaldiet (R2=0.6, p=0.012).” Evidence was also found for a strong correlation with reef physical structure. Large bodied parrotfish species had strong positive correlations with hard coral cover (Sparisoma viride, R2= 0.91, Sparisoma rubripinne, R2= 0.73, Scarus guacamaia, R2= 0.62, and Sparisoma chrysopterum, R2=0.6) highlighting the importance of coral to reefs rugosity and therefore fish community diversity and abundance. Sc iseri had the only strong negative correlation with turf algae (R2-0.66). This may indicate Sc iseri's population densities are still high enough to provide some control of turf cover. Sc iseri aslo had a strong positive correlation with Dictyota (R2=0.74) and could indicate Dictyota is colonizing space opened up by Sc iseri grazing. Future studies should investigate parrotfishes' direct consumption of algae including size and species of the fish and the amount consumed to further understand the dynamics at play in the parrotfish/algae relationship. It is important to understand parrotfishes' impact on benthic algae cover, including fleshy macroalgae species, turf algae and CCA, to help inform policy changes and support ecosystem based management efforts.