One of the largest and currently underappreciated reservoirs of marine microplastics may exist within the pelagic zone, the deep-sea water column of the open ocean, according to a study in Monterey Bay, California, published in Scientific Reports.
C. Anela Choy and colleagues used remotely operated vehicles and purpose-built samplers to collect and examine the distribution of microplastics in the Monterey Bay area, off the coast of California. The authors sampled 26,239 litres of seawater from depths of 5-1,000 metres, as well as two species - pelagic red crabs and giant larvaceans - which feed directly on particles of the same size as microplastics.
The authors found that polyethylene terephthalate (PET) - contained in single-use plastic bottles and packaging - was the most common plastic across all depths of the water column samples, as well as in the gastrointestinal tract of pelagic red crabs and in discarded mucus mesh filters produced by larvaceans. These structures, which are known as sinkers, are discarded after feeding and then sink to the seafloor. The findings suggest that larvacean sinkers function as vectors that transport microplastics from shallower depths to the seafloor. The highest concentrations of microplastics and the highest diversity of types of plastic were found at the base of the sunlit zone.
The findings suggest that microplastic pollution extends much further and more extensively into the waters, sediments and animal communities of the deep sea than previously assumed. Large-scale conservation and mitigation efforts are needed to assess the spatial and ecological scale of the problem, according to the authors.