Vulnerability to Global Environmental Change? Isotopic Inference of a Resident Population of Common Bottlenose Dolphins, Tursiops truncatus , in a Coastal Lagoon in the Southern Gulf of Mexico

Abstract

Through the isotopic composition of 211 samples of six different tissues (muscle, liver, heart, kidney, spleen, and lung) obtained from 51 Tursiops truncatus strandings over nearly a decade (2013–2022), this study evaluated the impact of environmental variations on a resident population in a coastal lagoon in the southern Gulf of Mexico. Isotopic data were corrected for lipid content and the Suess effect prior to analysis. Isotopic niche breadth was estimated using SIBER, and relationships with environmental variables (sea surface temperature, sea surface salinity, precipitation, and chlorophyll‐a) were assessed through correlation analyses and generalized linear models (GLMs). The results revealed (1) similar δ 13 C values among tissues and age classes but evident differences in δ 15 N, likely due to differences in metabolic and turnover rates; (2) a sustained annual decline in δ 13 C, suggesting a possible reduction in seagrass productivity; (3) seasonal differences in calf muscle tissue (δ 15 Ndry = 14.01‰; δ 15 Nnortes = 12.04‰), reflecting biogeochemical processes; (4) a marked influence of the strong 2015 ENSO event, associated with the lowest levels of Chlorophyll‐a; and (5) salinity variation in kidney tissue, with the lowest δ 13 C values (−18.27‰) recorded in 2020, a year of exceptional environmental conditions. These findings highlight the value of long‐term isotopic records from stranded T. truncatus as indicators for assessing population vulnerability to global change.

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