Influence of Ingested Microplastics on Copepod Fecal Pellet Density: Implications for the Transport of Plastics into the Deep Sea

Abstract: Microplastic ingestion by zooplankton represents an important pathway for the transport of buoyant plastics to the deep sea, yet its effects on fecal pellet properties remain poorly constrained. This study investigates how ingested microplastics influence copepod fecal pellet production and density using natural plankton communities. Copepods were collected via net tow from the Chesapeake Bay and incubated for 12 hours in whole-water food suspensions concentrated via reverse filtration along with 10 μm polystyrene beads. Particle size spectra were measured using an electronic particle counter at the beginning and end of incubations to estimate feeding rates. Following incubation, copepods and fecal pellets were separated and enumerated to determine egestion rates, and pellets were individually analyzed for size, density, and plastic content. Pellet density was measured by centrifugation into a density gradient (1.05–1.25 g cm⁻³). Pellet volume and incorporated microplastic bead counts were quantified via microscopy and image analysis to determine percent plastic volume. Preliminary results indicate that copepods readily accept microplastics as food and incorporate up to 36% plastic by volume into their fecal pellets, which can lead to impacts on pellet sinking behavior. Keywords (≤10): Chesapeake Bay; Copepods; Marine pollution; Microplastics; Particle flux; Vertical transport; Zooplankton ecology