Identifying potential natural and human influences on loggerhead sea turtle nesting, hatching, and emergence success

摘要

Florida beaches are vital for nesting loggerhead sea turtles in the Atlantic Ocean. Statewide variation in sea turtle nesting density is likely due to natural factors; however, variations in nesting density differences between beaches in a smaller region is likely due to anthropogenic activity. Since both sea turtle nest site selection and successful incubation are dependent on the beach environment, the uneven distribution of nesting in Florida could relate to morphodynamics, anthropogenic activities, or some combination of both. Two sites in Palm Beach County were utilized to examine potential natural and human influences on the variable sea turtle nesting density. Ocean Inlet, (OI) Park has been characterized as a low-density sea turtle nesting beach, located within a groin field immediately downdrift of the structured Boynton inlet in Boynton Beach. South Beach (SB) Park is in Boca Raton, approximately 1.5 km updrift of the structured Boca Raton inlet, and has been characterized as a medium-density nesting beach. A portion of SB was nourished in 2016 (just prior to the start of the main part of the sea turtle nesting season on May 1). Time-series beach profiles, cross-shore sediment characteristics, and internal beach temperature were collected in 2016 and used to evaluate the physical characteristics at the OI and SB sites. Sea turtle nest- ing, hatching, and emergence success from within 150 m of the beach profile locations were used to evaluate the influence of the groin field at OI and the nourishment at SB (as compared to the larger area monitored in each city). Despite variability in the surface sediment, morphology, and slope at OI and SB, which have been shown to influence nesting success, the difference in nesting success between locations was not statistically significant (OI=35%, SB=18%, P=0.100). Nesting success at the study sites were also comparable to the larger area, suggesting that neither the groin field at OI nor the adjacent nourishment project at SB were adversely impacting nesting as compared to other potential influences. For the 2016 nesting season, both sites were found to be medium density nesting beaches. In contrast to nesting success, hatching and emergence success between sites were significantly different. Hatching success at OI was 83% compared to 41% at SB. Emergence success at OI was 77% compared to 37% at SB. Eliminating several environmental parameters evaluated in this study, an emerging hypothesis is that processes associated with the variability in wave run-up, sediment color, and/or sorting may have altered nest moisture levels or gas exchange, thus contributing to the lower hatching and emergence success observed at SB as compared to OI.