For decades, plastic waste has ended up in the oceans, collecting itself thousands of meters below the surface and endangering the marine fauna there. For some marine animals, the plastic waste is also becoming a new habitat, as researchers have discovered in a deep-sea trench. They found almost 50 species of tiny snails, jellyfish and worms on the plastic. The garbage accumulations in the deep sea could therefore become a new hotspot of biodiversity.
In the seas, plastic waste collects in huge floating garbage whirlpools and sinks in large parts to the sea floor. The deep sea in the Arctic as well as in the Mariengraben, which is thousands of meters deep, and in some underwater canyons has long been contaminated with plastic, which has been preserved for decades despite the extreme conditions. This endangers the marine animals living there. For example, a PET fiber has already been detected in the abdomen of a species of flea that lives at a depth of over 6,000 meters.
What lives in the plastic waste of the deep sea?
How plastic waste affects the biodiversity of deep-sea fauna has now been investigated for the first time by a team of researchers led by Xikun Song from the University of Xiamen in China in several deep-sea trenches on the Xisha Islands in the South China Sea. To do this, the researchers first tracked the deposits of plastic in the ravines with the help of a submersible and collected a good 30 samples of the waste, which they examined for their polymer composition. Finally, they recorded the fauna living on the samples and determined the groups of organisms and their sexual maturity using the latest molecular biological and imaging methods such as micro-computed tomography (micro-CT) three-dimensional reconstructions.
The result: At a depth of up to 3,200 meters, around 52,000 plastic parts per square kilometer were stored there, which is a larger amount than in other trenches examined. The samples consisted of the plastics polyethylene (PE), polyethylene terephthalate (PET), polyvinyl chloride (PVC) and polypropylene (PP). The special thing about the collected plastic parts is that the scientists found a total of almost 1,200 organisms that apparently lived on and in the food packaging, bags or bottles. Song and his colleagues were able to assign the living things to almost 50 different types of organisms living on the sea floor. These included a number of animals living firmly in place, such as mushrooms, corals and barnacles, but also free-living parasitic flatworms and snails.
The most common inhabitants were the stuck polyps of umbrella jellyfish and mostly not yet fully grown shellfish, so-called arm pods (brachiopods), which externally resemble mussels. “Stages of reproduction such as snail eggs or the formation stages of jellyfish were noticeably frequent,” adds Bernhard Ruthensteiner from the Munich State Zoological Collection (ZSM).
Plastic changes biodiversity
“The abundance of shapes, but also the density of individuals on individual pieces, surprised us,” summarizes Ruthensteiner. According to the researchers, such a species-rich ecosystem has developed in the submarine garbage collections in the South China Sea that they call a new biodiversity hotspot. The accumulation of plastic waste in the deep sea promotes the spread of certain marine organisms and can thus lead to previously incalculable changes in marine ecosystems, the research team concluded. The occurrence of the organisms living in plastic waste is to be determined and monitored in future, heavily littered deep-sea trenches.
Source: Bavarian State Natural Science Collections, Article: Environmental Science & Technology Letters, doi: 10.1021 / acs.estlett.0c00967