Correlations between brevetoxin exposure, blood analytes, and reproductive success in nesting loggerhead sea turtles (Caretta caretta) and their offspring in southwest Florida, USA

Between October 2017 and February 2019, a red tide ( Karenia brevis ) bloom off southwest Florida resulted in the largest number of sea turtle strandings attributed to a single event. This study aimed to (1) quantify plasma brevetoxin concentrations in nesting loggerhead sea turtles, (2) determine brevetoxin concentrations in unhatched egg contents and dead-in-nest hatchling liver tissue samples, (3) assign foraging grounds to assess differences in brevetoxin exposure, (4) establish correlations between plasma brevetoxin concentrations and a suite of blood analytes in nesting females, and (5) identify impacts of brevetoxin exposure on emergence success. Between 2019 and 2022, blood was collected from nesting loggerheads, along with unhatched eggs and hatchling liver samples from corresponding nests for brevetoxin analysis. Maternal plasma brevetoxin concentrations were low relative to stranded turtles during blooms, ranging from <1.0 to 24.6 ng BTX mL −1 , and were higher in loggerheads foraging in the Gulf of Mexico than those using Subtropical Northwest Atlantic Ocean foraging grounds. Brevetoxin concentrations in egg and hatchling livers exceeded previous reports, suggesting maternal transfer of brevetoxins, presumably resulting from accumulation and mobilization from tissues during vitellogenesis. Correlations between brevetoxins and several blood analytes suggest potential effects on immune functions and possible subclinical health impacts, particularly during an active bloom in the 2021 nesting season. Emergence success was negatively correlated with hatchling liver brevetoxin concentrations. These findings suggest red tide events may act as environmental stressors with potential long-term impacts on sea turtle health and reproductive success.