Ecological Correlates of Green Turtle (Chelonia mydas) Abundance on the Nearshore Worm Reefs of Southeastern Florida Melanie Stadler † **, Michael Salmon † *, and Charles Roberts ‡ † Department of Biological Sciences Florida Atlantic University Boca Raton, FL 33431, U.S.A. ‡ Department of Geosciences Florida Atlantic University Boca Raton, FL 33431, U.S.A. ABSTRACT Stadler, M.; Salmon, M., and Roberts, C., 2015. Ecological correlates of green turtle (Chelonia mydas) abundance on the nearshore worm reefs of southeastern Florida. Journal of Coastal Research, 31(2), 244–254. Coconut Creek (Florida), ISSN 0749-0208. Juvenile green turtles (Chelonia mydas) differ in abundance on nearshore reefs, but why some sites are preferred over others is unknown. Our study had two objectives: to quantify site-specific differences in turtle abundance over time (1 y) and to determine what ecological factors were correlated with those differences. We conducted quarterly surveys on reefs in Palm Beach and Broward Counties, Florida, and compared reef sites with respect to (1) water depth, (2) algal abundance, (3) algal species richness, and (4) fluctuations in reef area caused by sand burial (which kills the algae used as forage by the turtles). Turtles were most abundant on reefs located in shallow water and exposed to bright ambient light. More turtles were also seen at sites where algae were both abundant and composed of many species. Reefs with those characteristics tended to remain uncovered by sand (‘‘stable’’) for longer time periods. We hypothesize that foraging by turtles on preferred reefs may prevent any one species of algae from dominating the site, making room for others to colonize. If true, then both physical stability (reef exposure time) and biological activity (turtle grazing) may make some reefs more attractive to turtles than others. ADDITIONAL INDEX WORDS: Habitat, ecological stability, algal diversity. INTRODUCTION Nearshore hard-bottom reef habitats (Anastasia formations and Sabellariid worm rock reefs) are found in shallow water along Florida’s east coast between Brevard and Miami-Dade counties (Kirtley and Tanner, 1968; Lindeman et al., 2009). These habitats are typically found within 200 m of the shoreline and at water depths of 7 m. These reefs run parallel to the shoreline and exist as either long tracts or as patches separated by areas of sand (Bush et al., 2004; Kirtley and Tanner, 1968). Nearshore hard-bottom reef habitats offer shelter for many animals and provide a substrate on which invertebrates and many types of marine algae can attach and grow (Moyer et al., 2003; Zale and Merrifield, 1989). As a result, these reefs support a diverse community of marine flora, invertebrates (e.g., arthropods, cnidarians, bryozoans, sponges), fish, and sea turtles (Lindeman and Snyder, 1999; Lindeman et al., 2009). Nearshore reef habitats are breeding and spawning sites for many marine organisms, but the majority of fishes and sea turtles found on these reefs are juveniles (Baron, Jordan, and Spieler, 2004; Moyer et al., 2003; Musick and Limpus, 1997). Habitats occupied by green sea turtles (Chelonia mydas) change with turtle size and age (Bolten, 2003; Guseman and Ehrhart, 1990; Musick and Limpus, 1997; Witherington, Hirama, and Hardy, 2012). Green turtles spend approximately 3–5 years in an oceanic stage of development (Reich, Bjorndal, and Bolten, 2007). During this time, they hide from predators in Sargassum mats (Carr, 1987; Smith and Salmon, 2009; With- erington, Hirama, and Hardy, 2012) and feed as omnivores, making shallow dives to capture prey near the surface (Bolton, 2003; Salmon, Jones, and Horch, 2004; Witherington, Hirama, and Hardy, 2012). Green turtles recruit to shallow develop- mental habitats as juveniles at a carapace length of about 25–35 cm (Bjorndal, 1997; Reich, Bjorndal, and Bolten, 2007). Return to coastal waters is accompanied by a gradual dietary shift, as the turtles begin feeding primarily on benthic macroalgae and seagrasses (Bjorndal, 1997). Green turtles are specialized to feed as herbivores, a feeding adaptation that, among marine turtles, is uncommon (Bjorndal, 1997). Juvenile turtles also use nearshore reef habitat for shelter. When resting, turtles often wedge their head and body under ledges present along the reef (Makowski, Seminoff, and Salmon, 2006; Mott and Salmon, 2011; Seminoff, Resendiz, and Nichols, 2002). Developmental habitats are those occupied by marine turtles for portions of their ontogeny between the juvenile and adult life history stages (Bass and Witzell, 2000; Bjorndal and Bolten, 1997; Bolten, 2003; Meylan, Meylan, and Gray, 2011; Musick and Limpus, 1997). Carr (1987) first used this term with regard to sea turtles when he recognized that most sea turtles only spent a portion of their lives as oceanic creatures and returned to nearshore waters to complete growth to sexual maturity. He used the term ‘‘developmental migrations’’ (Carr, 1980) to DOI: 10.2112/JCOASTRES-D-14-00070.1 received 11 April 2014; accepted in revision 26 July 2014; corrected proofs received 11 September 2014; published pre-print online 27 October 2014. *Corresponding author: salmon@fau.edu **Present address: Gumbo Limbo Nature Complex, 1801 North Ocean Boulevard, Boca Raton, FL 33432, U.S.A. Ó Coastal Education and Research Foundation, Inc. 2015 Coconut Creek, Florida March 2015 Journal of Coastal Research 31 2 244–254