Microplastics, Major Problem
Microplastics are small pieces of plastic less than 5 millimetres long. You may have thought that something so small couldn’t affect a large vertebrate like, say, a sea turtle. But you’d be wrong.
Microplastics are either manufactured as microbeads for cosmetics or microfibers for clothes, known as primary microplastics, or created by the breakdown of larger plastic pieces into smaller ones, known as secondary microplastics.
Scientists have discovered that these tiny pollutants could indeed have a huge impact on animals, but perhaps not in the way you might think. They came to this conclusion following research into the amount and type of microplastics that are present at loggerhead turtle nesting grounds on some of Florida’s northern beaches.
It turns out that on these beaches (10 of the most important nesting sites in Florida for the Northern Gulf of Mexico loggerhead population), microplastics are everywhere – they were found at every single site.
Worryingly, the majority of the pieces were located at the dunes, which is predominantly where the turtles nest.
The reason that this is a problem is because microplastics can change the composition of sandy beaches. Plastics warm up when exposed to heat, especially dark plastic, and they tend to retain large amounts of heat in response to comparatively moderate increases in temperature. When combined with sand, microplastics can therefore increase the temperature of the sand.
How does this affect the turtles? Well, the environment in which their eggs incubate can influence hatching success, the size of the hatchlings and their gender. The sex of marine turtles is determined by the sand temperature during incubation – warmer sand at temperatures between 29.5 and 34 degrees Celsius produces females, colder sand between 24 and 29.5 degrees Celsius produces more males. (A handy way to remember this, for a pub quiz, say, is ‘hot chicks and cool dudes.’ You’re welcome.)
Warmer sand temperatures caused by the presence of microplastics at their nesting sites may bias the sex ratio of turtles towards producing more females – clearly this would impact the future reproductive success of the loggerheads. And that’s before we even consider what the toxic chemicals that leach out of the heated microplastics are doing to the nesting environment.
The skewed sex ratio is a problem not confined to Florida. Another study on the beaches of Cyprus, home to loggerhead and green turtles, found plastic at all 17 nesting sites that they examined. At the surface, they found up to 130,000 pieces of plastic per cubic metre, the second worst level ever recorded on a beach (the worst being Guangdong in South China). Even more concerning was that they also found an average of 5,300 particles of plastic per cubic metre at depths of 60 cm.
In Cyprus, the beaches are located far from any industrial practices and aren’t visited by large numbers of people. Therefore, the plastic is arriving on ocean currents. It seems as though beaches are acting as “sinks” for marine microplastics, becoming key areas of contamination.
Everywhere the scientists conducting this research looked, they found plastic. Vulnerable species like sea turtles are bearing the brunt of decades of our irresponsible waste.