Macroalgal foraging preferences of juvenile green turtles (Chelonia mydas) in a warm temperate/subtropical transition zone

Abstract

Understanding resource use and foraging requirements is important for the recovery of threatened and endangered marine turtles. Throughout their range, an increasing number of juvenile green turtles (Chelonia mydas) has been observed foraging and sheltering within man-made structures. These “artificial habitats” are ecologically important as they support the growth of attached macroalgae, a primary food resource of juvenile green turtles. A population of juvenile green turtles in the Trident Basin at Port Canaveral, Florida, USA (28.41°N, 80.59°W), has historically exhibited strong site fidelity. The purpose of this study was to compare the foraging of juvenile green turtles with the availability of macroalgal resources. Foraging (lavage) samples from 94 juvenile green turtles during a 2-year study period from September 2008 through April 2010 were analyzed with the data from two previous studies (1997 and 2002) to determine the patterns of foraging habits through time. Turtles predominantly foraged on species of red (Rhodophyta) and green (Chlorophyta) macroalgae; however, opportunistic foraging on flotsam and invertebrates was common. Selection for certain rhodophytes (i.e., Gelidiopsis planicaulis, Grateloupia filicina, and Hypnea spinella) and chlorophytes (i.e., Cladophora liniformis, Ulva flexuosa, U. lactuca, and U. prolifera) varied by sampling period. Temperature-driven changes in the macroalgal species composition drove inter-annual differences in foraging content between 2002 and 2010. In addition, after an extended cold event, foraging samples from several turtles contained macroalgae not present in the Basin which suggested that turtles moved out of the Basin to forage during this time or newly emigrated. Establishing baseline resource utilization is instrumental for identifying the quality and function of natural and artificial habitats supporting juvenile green turtles, as their populations continue to recover around the globe.