A new study from Florida State University shows that increasing microplastic accumulation along the Gulf’s beaches could alter the composition of shoreline sand and jeopardize the sensitive incubation environments of Loggerhead sea turtles.
The Loggerhead sea turtle (Caretta caretta) is the most abundant of all the marine turtle species in U.S. waters. But persistent population declines due to pollution, shrimp trawling, and development in their nesting areas, among other factors, have kept this species on the threatened species list since 1978.
For the study, EOAS student researcher Valencia Beckwith surveyed the Northern Gulf of Mexico Loggerhead Recovery Unit’s 10 most important loggerhead turtle nesting sites in Florida. Sand samples collected throughout the region revealed that microplastics were present at every site, with the highest concentrations of microplastics (59.9%) were found consistently in the dunes, where sea turtles tend to nest.
One of the main reasons this form of pollution could have detrimental effects to sea turtles is that plastic has a tendency to retain large amounts of heat in response to comparably moderate increases in temperature. If enough plastic is present in a sandy environment, the area could experience measurable temperature increases and this dynamic is of particular concern in sea turtle nests.
“Sea turtles have temperature dependent sex determination, which means their sex is determined by the sand temperature,” Fuentes said. “Changes in incubation temperatures might modify the sex ratios produced on these nesting beaches, but at this stage we don’t know how much microplastic is needed to see those changes.”
The southeastern United States hosts the world’s largest nesting aggregation of the loggerhead turtle. The Northwest Atlantic Ocean’s loggerhead nesting aggregation is considered to be the largest in the world, with Florida hosting approximately 90 percent of the nests associated with this aggregation
Loggerhead turtles nest at intervals of 2 to 4 year and lay 3 to 6 nests per season, approximately 12 to 14 days apart. They lay an average of between 100 to 126 eggs in each nest with eggs incubated for about 60 days.
The highly migratory behavior of sea turtles makes them shared resources among many nations. Thus, conservation efforts for sea turtle populations in one country may be jeopardized by activities in another. Protecting sea turtles on U.S. nesting beaches and in U.S. waters alone, therefore, is not sufficient to ensure the continued existence of the species.
In subsequent research, Beckwith and Fuentes plan to expand upon these findings and investigate the specific ways that microplastic might alter the temperature profile of the sediment on important nesting beaches.
“The first step was to see whether sea turtles are exposed to microplastics,” she said. “Next we’ll explore its potential impacts.”
Their findings were published in the journal Marine Pollution Bulletin.
Valencia K. Beckwith, Mariana M.P.B. Fuentes. Microplastic at nesting grounds used by the northern Gulf of Mexico loggerhead recovery unit. Marine Pollution Bulletin, 2018; 131: 32 DOI: 10.1016/j.marpolbul.2018.04.001