Lucas Futey, Claire Boudreaux, Timothy Clay

The Diamondback Terrapin is a brackish water turtle that resides in intracoastal marshes and is often fouled by epifaunal invertebrates, most commonly barnacles. Diamondback Terrapin are a sexually dimorphic species resulting in larger females with differential prey selection. Therefore, sexual dimorphism may cause differential habitat use (cordgrass vs. mangrove) and may allow for variation in barnacle presence and quantity. I expect female terrapin occurring in higher salinities and habitats with greater mangrove presence to have a higher likelihood of having barnacles and more barnacles. Barnacle attachment was quantified in populations of Diamondback Terrapin at Elmer’s Wildlife Refuge (EWR) and East Grande Terre (EGT) in Grand Isle, Louisiana was recorded from 2021 to 2024. Females were statistically more likely to have barnacles and have a higher quantity of barnacles. Increased presence and quantity of barnacles was also found to have a significant relationship with increasing carapace length and varied by sex. There was no significant difference in the presence of barnacles between populations, however terrapin at EWR had significantly more barnacles than terrapin at EGT. Sex was a significant factor independent of carapace length suggesting that the sexes may behave and use the environment differently, with females potentially spending more time in aquatic environments in the presence of mangroves.

Kaya Floyd, Hector Douglas

Ocean heat content was anomalously high in the Caribbean Sea during much of 2024, driven up in part by the 2023-2024 El Niño-Southern Oscillation (ENSO). We anticipated that this could affect the availability of prey species for tropical seabirds. We characterized diets of three species  of seabirds: sooty terns (Onychoprionis fuscatus), brown noddies (Anous stolidus), and white-tailed tropicbirds (Phaethon lepturus), at Culebra National Wildlife Refuge in Puerto Rico. During June 2024, we collected blood and feather samples as well as samples of prey fish. We analyzed these for stable isotopes (δ13C, δ 15N). We extended our analysis for a sample of sooty terns to include feathers grown during early Fall 2023. These samples reflected diets prior to the onset of the ENSO. Using paired t-tests, we found evidence for dietary shifts between early Fall 2023 and Winter 2023-24 (t(8)=-4.9, p=0.001) and between Fall 2023 and June 2024 (t(8)=2.58, p=0.03). Some tropical seabirds like the sooty tern benefit from the foraging activity of predatory fish, but high ocean temperatures could exclude these predatory fish from the surface layer, making the prey fish less available.