Coral reefs are some of the most diverse habitats on our planet, sheltering thousands of species of fish. Despite their importance, however, reefs are increasingly suffering from rising temperatures and severe plastic pollution – with plastic bags, bottles, and packaging present in nearly every existent reef.
Although often ignored by scientists and environmentalists, microplastics – tiny plastic fragments measuring less than five millimeters – are just as prevalent in coral reefs all over the globe, and pose significant dangers.
In a new study published in the journal Global Change Biology, a research team led by Jessica Reichert, a postdoctoral fellow at the Justus Liebig University Giessen (JLU), has found that over four million pounds of microplastics are stored in coral reefs all over the world each year, causing bleaching and tissue necrosis in these marine animals.
In a previous study published in the journal Environmental Pollution, Reichert and her team investigated the effects of microplastics on six different coral species. They looked at how the reefs responded to the presence of microplastic particles in their environment, and how exposure to these materials affected their health.
The scientists exposed corals to increasing concentrations of microplastics under laboratory conditions. They discovered that while some corals confused the microplastics with food, eagerly ingesting them, others showed various forms of rejection, such as producing mucus in response to them.
After four weeks, regardless of their attitude toward the pollutants and whether they consumed them or not, five of the six species of corals under investigation displayed significant signs of ill health, such as bleaching and tissue necrosis.
“Our study clearly indicates that microplastics are yet another human-made stress factor for corals and that they are very likely to contribute to further deterioration of coral reefs on our planet,” said Dr. Reichert.
The new study shows that corals all over the world are now serving as a long-term sink for microplastic. After 18 months of exposure, most of the pollutants ended up inside the corals’ skeleton rather than tissues.
“In our study, particles were found 15 times more frequently in coral skeletons than in tissues,” wrote the study authors. “This shows that the coral tissue is likely only a temporary sink before particles are egested or permanently translocated to the skeleton.”
According to Reichert, it is not yet clear what consequences this type of storage might have for the corals and for reef stability and integrity. However, it might definitely pose “an additional threat to coral reefs worldwide.”