Over the last few weeks, the FSU Marine Turtle Research, Ecology, and Conservation Group (FSU MTRECG) has had the privilege of collaborating with the University of Exeter on a global survey of microplastic pollution of sea turtle nesting beaches. My labmates Hector Barrios-Garrido, Kelly Soluri, Emily Drobes, and I have collected a total of 120 sand samples from 12 beaches across the Florida Panhandle and Alabama for analysis of their microplastic content. These beaches span from Alligator Point, St. George Island, and the St. Vincent National Wildlife Refuge in the east to Fort Morgan and Gulf Shores in the west. This collaboration is an expansion of research efforts by both institutions over the last several years to categorize pollution levels at sea turtle nesting beaches.
Microplastics are defined as any plastic material between 1 and 5 mm in diameter. These can either be manufactured at that size (e.g., microbeads in an abrasive face wash) or reach this size due to weathering of larger marine debris within the environment. A lot of recent literature has been published on the prevalence of these microplastics (and larger marine debris) in the digestive tracts of numerous marine animals across the food chain – from plankton and shellfish to turtles, birds, and whales. Once ingested, this debris can result in blockages of the digestive tract, starvation, and poisoning. The toxic effects of ingestion can be transferred up the food chain through a process called bioaccumulation. However, these plastics do not need to be ingested to have an environmental impact.
Plastics have different thermal properties than sand – meaning they heat up, cool off, and transfer heat differently. The exact difference depend on the types of plastic and sand. In the case of sea turtles, which rely on certain environmental conditions to properly incubate their eggs, high levels of microplastic have been theorized to interfere with embryonic development. Sea turtles have temperature-dependent sex determination (TSD). Unlike humans who have X and Y chromosomes to determine sex, in species with TSD the temperature during incubation determines the production of sex hormones (e.g., testosterone) and therefore the sex of the individual. In sea turtles, warmer temperatures result in more female hatchlings – think “hot chicks and cool dudes”. But, get too warm, and the embryos have trouble developing properly (e.g., misshapen scutes in their shells, cleft palate, lack of pigmentation, poor muscular development, etc.) and may die before hatching.
More microplastics in the sand = warmer sand. Warmer sand = more female hatchlings and/or more physical deformities and mortality.
Microplastics may also leach toxicants into the surrounding sand as they continue to decay. These can be transferred into the developing embryos as the eggs exchange water and air with the neighboring sand. The absorption of these toxicants may have both lethal and sub-lethal impacts, depending on the amount and type of toxicant absorbed.
To date, both of the thermal and toxic impacts of microplastic pollution at sea turtle nesting beaches remains theoretical. However, global collaborations such as this project and ongoing research efforts at FSU MTRECG are seeking to quantify both the scale of the microplastic problem and the likelihood of negative impacts to sea turtle reproduction. A recent update from Dr. Brendan Godley of the University of Exeter, the instigator of this collaboration, has indicated the involvement of 60 programs from around the world in the collaboration. FSU MTRECG’s samples will be 120 of hundreds of samples in the most extensive survey of its kind completed to date. Results of the collaboration are expected between 2019 and 2020, so check back later for updates!
Check out these recent publications from both FSU MTRECG and the University of Exeter to get a sense of the potential problem:
Beckwith, V.K., and M.M.P.B. Fuentes. 2018. Microplastic at nesting grounds used by the northern Gulf of Mexico loggerhead recovery unit. Marine Pollution Bulletin 131A: 32-37.
Duncan, E.M., et al. 2018. The true depth of the Meditteranean plastic problem: Extreme microplastic pollution on marine turtle nesting beaches in Cyprus. Marine Pollution Bulletin 136: 334-340.