Grant: 22-024R
Project Title: Proximate nutritional values and tissue assimilation of macroalgae for juvenile green turtles foraging in algal-dominated ecosystems
Project Manager: Karen G Holloway-Adkins, PhD
Organization: East Coast Biologists, Inc. (Non-Profit Organization)
Grant Amount: $19,831.00
Completion Date: 2024-12-16
Summary: The purpose of this study is to determine the proximate nutritional value of macroalgae consumed by juvenile green turtles and estimate assimilation in tissues using stable isotope analyses. The proximate analysis of food resources (e.g., protein, lipid, carbohydrate) consumed by wild juvenile green turtle populations in Florida has not been explored. As green turtle populations are beginning to recover in some areas, evidence suggests a trophic cascade is occurring in seagrass communities. In east central and south Florida, aggregations of juvenile green turtles in coastal and inlet habitats forage almost solely on macroalgae, particularly, species of turf algae that are inherently difficult to identify. Currently, there is no evidence to suggest that warm-temperate/subtropical macroalgal-dominant communities undergo processes similar to seagrass communities. However, besides kelp forest community and coral-algal dynamics, there has been little focus on macroalgal communities regarding large vertebrate grazer impacts. Baseline data on turtle foraging are necessary to adequately measure habitat modification wrought by climate change, coastal development, and pollution inputs. 
Results: Water quality and algae sample collection: Algae were predominantly collected in <1 m water depth from three different algal-dominated locations in Brevard (Trident Basin and Mid Reach nearshore hardbottom reef or NHR) and St. Lucie (Walton Rock NHR) counties. The algae were sorted by presumed species, then volumes of each species were subdivided based on the amount needed for analysis or sequencing [i.e., proximate nutritional value assessment, DNA sequencing, stable isotope analysis (SIA)]. A voucher sample was retained for all species collected and pressed until completely dried. Vouchers were labeled and shipped for archival in the UNCW Herbarium. Lavage samples: Lavage samples (n = 28) were analyzed from a subset of juvenile green turtles captured by University of Central Florida's Marine Turtle Research Group at the Trident Basin in August 2022 and January 2023. In addition, lavage samples (n = 28) were analyzed for juvenile green turtles captured over NHR (n = 22) and mitigation (or artificial; n = 6) reefs (ARs) in Brevard County. DNA sequencing: Nine of the macroalgae sequenced had not been previously included in floristic treatment of Florida marine macroalgae. Some species found in the Trident Basin were from altogether different ocean basins (e.g., Taiwan, Peru). There is at least one species that is a confirmed new report for Florida. Stable Isotope Analysis: Tissue and scute samples were collected from 21 juvenile green turtles captured on Mid Reach NHR and compared with the SIA values from 41 items (38 macroalgae and 3 invertebrates) locally present and/or found in lavage samples.