Estimating the Contribution of Zooplankton Fecal Pellets to Marine Suspended Particle Pools

Zooplankton fecal pellets are a major contributor to the vertical flux of particulate organic matter (POM) through the marine water column and into sediments. However, the contribution of zooplankton fecal pellets to POM is difficult to quantify. Current estimates and models often rely on visual identification of pellets to determine their relative input to POM pools, but these methods only capture fecal pellets that are intact or recognizable. Both microbial alteration and coprohexy redistribute fecal pellet carbon into small and suspended particle pools, where particles are too small to visually identify. Lipid biomarkers are also used to quantify detrital fecal pellet contributions, but fecal pellets are not reliably biochemically distinct from zooplankton food sources.

We used bulk and compound specific stable isotope analysis (CSIA) to characterize zooplankton fecal pellets and detect their contribution to POM in the marine environment. We propose that these analyses can provide an isotopic “fingerprint” of the zooplankton fecal pellet end-member in POM deriving from mixed sources. We present a preliminary quantitative model to estimate fecal pellet contributions to POM based on these data and estimate the contribution of zooplankton fecal pellets to suspended and sinking particles in subtropical and subarctic water columns. Our results illuminate the complex roles that zooplankton wastes play in particle flux.