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ESR prepress abstract   -  DOI: https://doi.org/10.3354/esr01276

Hawksbill and green turtle niche overlap in a marine protected area, U.S. Virgin Islands

Melissa A. Moorehouse. , John D. Baldwin, Kristen M. Hart*

*Corresponding author:

ABSTRACT: Studying how species interact with their environment and other co-occurring species are two main aspects of ecology. For marine turtles, ocean currents drive migratory routes and may determine the location of surrounding foraging grounds. As a result, circumglobal species like the hawksbill turtle, Eretmochelys imbricata, and green turtle, Chelonia mydas, adapt to diverse foraging habitats, and employ varied feeding strategies. Dietary specializations may reduce competition for available food and space resources between co-occurring hawksbill and green turtles in U.S. Virgin Island shallow reef habitats. This study analyzed isotopic data from immature hawksbills (n=49, range 18.7 cm – 49.8 cm straight carapace length (SCL)) and green turtles (n=225, range 24.1 cm – 69.4 cm SCL) to examine foraging niche. We used δ15N values as an indicator of trophic positioning and δ13C values as a habitat variable. Turtles were hand-captured across an 8-year period (2012-2019) which facilitated distinction of isotopic patterns in both the environment and among individual turtles. Understanding variations in habitat, community dynamics, and dietary consumption allowed us to utilize a five-point framework to translate isotopic space to foraging niche. We found the site’s relatively stable environmental conditions allow for isotopic overlap between hawksbills and green turtles despite the specialized feeding strategies each employ. We also underscore the need to evaluate species-specific tissue turnover estimates as evidenced by the influence of tropical storms on recaptured turtle isotopic signatures. These findings inform our understanding of resource use for these imperiled species at our study site and are useful for future global isotopic comparisons.