Size as the master trait in modeled copepod fecal pellet carbon flux

Abstract

Zooplankton fecal pellet flux is a highly variable component of the biological carbon pump. While fecal pellets can comprise 0 to nearly 100% of particulate organic carbon collected in sediment traps, mechanisms for this variability remain poorly understood. Fecal pellet carbon flux is a complex function of several variables. We present a model that incorporates individual‐scale metabolic processes to determine fecal pellet production rate, the relationship between body size and fecal pellet size, the relationship between fecal pellet size and sinking rate, and a function representing the breakdown of particles in the water column. When applied to copepod communities sampled by the continuous plankton recorder in the Gulf of Maine over 25 years, a seasonal pattern of fecal pellet carbon flux emerges. The interannual flux time series produced by the model reflects known oceanographic perturbations and shows how organism‐scale processes can be scaled up to explain ecosystem level variability. We conclude that fecal pellet carbon flux in the Gulf of Maine is driven by copepod community size structure and copepod abundance, and that the fraction of fecal pellet carbon that reaches depth is a function of copepod size, rather than abundance. Changes in the physical environment which alter the size composition of the copepod community lead to variability in fecal pellet carbon flux. Our results indicate that incorporating size composition into biogeochemical models can more accurately constrain zooplankton‐mediated carbon flux.

Trait biogeography of marine copepods – an analysis across scales

“…Copepod faecal pellets may contribute a significant but highly variable (0–100%) fraction to the vertical material fluxes in the ocean (Turner ), and body size of copepods appears to be the main determinant of this fraction (Stamieszkin et al . ): small copepods produce small faecal pellets that are mainly recycled in the upper ocean, whereas large copepods produce large pellets that rapidly sink to the seafloor. Body‐size diversity of mesozooplankton communities, which are typically dominated by copepods (Verity & Smetacek ), is furthermore positively correlated with the transfer efficiency of primary production to higher trophic levels (García‐Comas et al .…”

“…The distribution of body size in copepod communities has implications for the fate of the primary production, and determines whether it is recycled in the upper ocean, transported to the sea floor via faecal pellets, or channelled towards higher trophic levels. Copepod faecal pellets may contribute a significant but highly variable (0-100%) fraction to the vertical material fluxes in the ocean (Turner 2002), and body size of copepods appears to be the main determinant of this fraction (Stamieszkin et al 2015): small copepods produce small faecal pellets that are mainly recycled in the upper ocean, whereas large copepods produce large pellets that rapidly sink to the seafloor. Body-size diversity of mesozooplankton communities, which are typically dominated by copepods (Verity & Smetacek 1996), is furthermore positively correlated with the transfer efficiency of primary production to higher trophic levels (Garc ıa-Comas et al 2016): the optimal prey size of primary consumers depends on their body size, and therefore communities of primary consumers with diverse body sizes feed efficiently on a range of prey sizes and harvest the phytoplankton communities more exhaustively.…”

Carbon Budgets of Mesozooplankton Copepod Communities in the Eastern Atlantic Ocean—Regional and Vertical Patterns Between 24°N and 21°S

“…However, large contributions of small copepod species in the (sub)tropics reduce the strength of the biological carbon pump, which is why our values may be overestimated in these regions. Although small copepods produce more fecal pellets per time, the pellets are smaller with lower sinking velocities and thus longer exposure to coprophagy, coprohexy, and bacterial degradation (Stamieszkin et al, ). Yet in the Sargasso Sea, the annual contribution of fecal pellets to carbon fluxes was about three times higher than active carbon transport by diel vertical migrations (Steinberg, Lomas, & Cope, ).…”

“…Many processes that determine the export flux are biologically controlled, and the magnitude and attenuation of this flux, that is, the strength and efficiency of the biological pump, vary with depth, season, and regional variation in the ecosystem structure (Buesseler & Boyd, ). Fixed organic carbon in the euphotic zone is modified by community respiration, zooplankton grazing, and fecal pellet production as well as particle aggregation and microbial decomposition processes, which altogether contribute to the portion of biogenic particles sinking out of the euphotic zone (e.g., Boyd & Trull, ; Buesseler & Boyd, ; McDonnell & Buesseler, ; Siegel et al, ; Stamieszkin et al, ; Stukel et al, ; Wassmann, ). In total, 34–63% of carbon produced by global marine primary production (PP) is consumed by epipelagic mesozooplankton communities (Hernández‐León & Ikeda, ).…”

“…Changes in zooplankton biomass and community structure significantly affect the export of organic material to the deep ocean (Boyd et al, ; Ducklow et al, ; Stamieszkin et al, ; Steinberg, Lomas, & Cope, ; Wilson & Steinberg, ). The fraction of phytoplankton carbon leaving the euphotic zone may vary between 33% and 70%, depending on the trophic behavior and structure of the prevailing zooplankton community (Wassmann, ).…”