Meeting Abstract
At reefs dominated by higher trophic level piscivores, variations in distribution and abundance of prey species mediate community composition. Understanding prey patchiness provides important information about the community and aids in the interpretation of surveys monitoring the status of protected areas. We asked how distribution and abundance of small prey fish changed over space and time at Gray’s Reef National Marine Sanctuary (GRNMS; off Georgia, USA) by comparing prey density (fishes <11cm TL in 100m2 segments) at reefs inside and outside an area closed to fishing using data derived from Simrad EK60 split-beam sonar surveys in 2011, 2012, and 2013. Surveys were conducted at dawn and dusk at 6 reefs in 2011 and 2012, and 5 reefs in 2013. Overall there were significant differences between years, fishing treatments, reefs, and time of day (GLM Procedure; p<0.05). Noteworthy comparisons within treatment levels revealed significantly higher prey densities in 2012-13 at sites outside of the no-fishing zone. There were also significant temporal differences in prey density: 2011 had the lowest fish density and 2012 the highest. In addition, comparison of the indices of mean crowding revealed significant changes in the distribution of the prey population along reefs, with more clumping of prey in 2012 and 2013. This initial assessment of variation in prey resources at GRNMS suggests that abundance and patchiness can provide a useful indicator for the presence of top predators on reefs and potentially aid in the management of such ecosystems.
