Marine Plastic Pollution in the South Pacific

Abstract

Marine plastic pollution has become one of the most relevant environmental issues in the recent years. It is associated with an array of human activities on land and at sea. The mass production of plastics started in the 1950s, short after which numerous adverse effects on marine organisms had been documented. In the recent years, plastic ingestion by marine fish and shellfish has been of increased interest to the scientific community and general public, particularly with respect to human health implications. Fish are an important food source for South Pacific (SP) island countries, yet there is little information on contamination of commercial marine fish species by plastic. In response, I reviewed available literature on plastic ingestion by marine fish in the wild published by July 2017 (Chapter 2), and found that 68 % of examined 370 fish species were reported to contain marine plastics. However, although this is a high percentage, it is most likely an underestimate due to small sample sizes and deficient analytical methods. A significant positive relationship was found between the detection of plastic and sample sizes. Significantly greater ingestion rates were obtained with robust analytical methods which included chemical digestion of the organic portion of the gut content, as opposed to naked-eye or microscopic analysis. Furthermore, of all examined commercial fish species (288) in the review, 71 % contained plastics. I performed a broad-scale assessment of plastic ingestion by 34 fish species commonly present in the diet of South Pacific inhabitants collected from Auckland, Samoa, Tahiti and Rapa Nui (Easter Island). Almost a quarter of all individual fish ingested plastic, and only one species did not contain any plastics. Rapa Nui fish exhibited the greatest ingestion rates (50.0 %), significantly greater than in other three locations. Rapa Nui is located within the South Pacific subtropical gyre, where the concentration of marine plastics is high and food is limited. Plastic was also found in prey, which is the first confirmation of trophic transfer of microplastics from prey to predatory fish in field subjects. Finally, I carried out a study on plastics contamination of the surface waters and shore and benthic environment, on macroscopic and microscopic level, in Vava’u archipelago, Tonga, which is the first study on plastics pollution in multiple ocean compartments in the Pacific islands. Besides being a baseline study, it also included methodological investigation. Concentrations of macro- and microscopic plastic debris were greater along the shores and in the shore sediments, than on the seafloor and benthic sediments. Microscopic assessments of surface waters revealed high concentrations (338,437.5 ± 42,131.8 particles km-2), comparable to the concentrations obtained in the South Pacific subtropical gyre. As opposed to the commonly used standard nets with 333-μm mesh, the size of the mesh used for sampling Vava’u surface waters was 100 μm. The result shows that the standard nets most likely greatly underestimate the quantities of microplastics in the surface waters. Additionally, we used CaCl2 salt to create a high-density solution of 1.40 – 1.45 g cm-3 for separation of denser types of plastics, such as PET and PVC, while the commonly used salt is NaCl which reaches a maximum density of 1.2 g cm-3. However, the results of the efficiency of density separation with CaCl2 are inconclusive, as in many studies in which 1.2 NaCl solution was used particles denser than the solution were recovered as well. In conclusion, this research shows that macroscopic and microscopic plastic debris is commonly present in the South Pacific marine environment, as well as commercial marine fish.