SEABIRD TRANSFER OF MARINE MICROPLASTIC FIBERS TO TERRESTRIAL SOILS VIA THE ACCUMULATION OF GUANO AT PALMYRA ATOLL, NORTHERN LINE ISLANDS, CENTRAL PACIFIC OCEAN

Plastic pollution and its physical breakdown affect nearly every marine and freshwater ecosystem. In the Pacific Ocean, plastic debris accumulates at high concentrations in coastal waters near population centers, in gyre-controlled oceanic “garbage patches,” and in lithic and organic sediments of nearly every beach and estuary surveyed to date. Away from the gyre-induced garbage patches, concentrations of microplastic particles (MPs; < 5mm) in surface waters of the open Pacific Ocean are exceedingly low; however, bioaccumulation through the oceanic food chain is occurring. This study investigates the animal transfer and accumulation of MPs from the ocean to terrestrial soils at Palmyra Atoll (“Palmyra”), a U.S. territory in the Northern Line Islands Archipelago (5.88°, -162.08°). We document the ocean-to-terrestrial transfer of microplastic fibers through an analysis of the excrement (guano) collected from beneath roosting and nesting sites inhabited by Palmyra’s resident population of ~25,000 Red-footed Booby, Sula sula (RFBO). RFBOs are tree-nesting, obligate marine foragers that prey exclusively on flying fish and squid on daily flights, averaging 60 km from the atoll. To our knowledge, this is the first study to document the transfer of marine microplastic particles to the soils of tropical atoll ecosystems following a two-vector (minimum) transport process involving marine prey and predatory birds.

RFBO guano was collected from stems and leaves below six nesting sites across the atoll. Guano samples were dried, weighed (0.72 kg total), and prepared via wet oxidation. Microplastic fibers were detected via stereo microscope and analyzed for chemical composition via Raman spectroscopy. Guano from all six sampling locations contained microplastics, averaging 0.2 (0.04 – 0.61) MP fibers/g of dry guano. Polyethylene terephthalate (PET) was the dominant observed plastic. RFBOs add ~140 dry tons of guano to Palmyra’s soils annually, and this quantity of excrement likely contains 26-30 x 10⁶ microplastic fibers. Our results indicate that even exceedingly remote terrestrial oceanic ecosystems are not immune from the sedimentary accumulation of long-lived synthetic fibers, despite being located thousands of kilometers from hotspots of plastic waste injection and accumulation.