Comparing microplastic distribution and potential risk to zooplankton in American Samoan coastal waters and the Equatorial Pacific

Abstract

Microplastics (MPs) are a growing threat to marine organisms due to risks of ingestion and toxin bioaccumulation. Zooplankton are especially vulnerable to MPs and are important as a key piece of the trophic web. However, MP abundance, type, and effect on zooplankton communities in the southwest equatorial Pacific remains understudied. Using data from a cruise on the R/V Thomas G. Thompson between December 28th, 2023 – January 10th, 2024, this study analyzes MP abundance and type, and compares it to zooplankton relative abundance to determine MP pollution and risk to zooplankton populations around American Samoa and the Equatorial Pacific. I hypothesized that higher levels of microplastic pollution would be found near American Samoa than at the Equatorial Pacific. I further hypothesized that a correlation exists between MP abundance and relative abundance of zooplankton species at-risk of MP ingestion. Zooplankton and MP samples were collected near American Samoa and the Equatorial Pacific using a 333 μm mesh Manta net. A dissecting scope was used to identify and count zooplankton and MPs. In comparing MP type and distribution, I found that the average MP concentration at coastal stations was 5.7 x 10-3 MPs/m3, while the average MP concentration at equatorial stations was 1.3 x 10-4 MPs/m3. 88% of all MPs collected were microfibers. However, no correlation between zooplankton abundance and MP abundance was found. Further research in the region is critical due to the direct connection to waste, quality of life, industry, subsistence, and ecosystem and human health in the tropical Pacific.