The effect of phytoplankton properties on the ingestion rate of marine snow by Calanus pacificus

The aggregation of phytoplankton into marine snow provides a mechanism by which smaller particles can coagulate to form larger particles, as well as creating microcosm environments for microbial dynamics. Marine snow can be readily transported to the deep ocean, consumed at various depths, or sequestered from the atmosphere on millennial time-scales. Zooplankton interacting with these large carbon-rich aggregates can obtain nutrition in environments where the phytoplankton size-spectra is small and not directly available, enhancing the possibility of obtaining adequate nutrition in environments dominated by small cells. In addition, interactions between zooplankton and marine snow can result in fragmentation, thus affecting the particle sinking rate and changing the export of carbon. Unfortunately, these interactions are understudied and poorly understood. Our research focuses on the factors affecting copepods feeding on marine snow, and will provide insight into the role of this food source in planktonic trophic dynamics and export of carbon to depth.

We conducted a series of grazing experiments using gut pigment and stable isotope methods to quantify the ingestion rate of the copepod, Calanus pacificus, on marine snow aggregates in comparison to their ingestion rate on individual phytoplankton. We also examined how the ingestion of copepods on marine snow was affected by the phytoplankton species and phytoplankton growth phase from which the aggregates were formed. Results demonstrate that marine snow is consumed at comparable or higher rates than individual phytoplankton and may partially depend on phytoplankton growth phase. This suggests that marine snow is likely an important food source for copepods but that its role in planktonic food webs may differ depending on the stage of phytoplankton blooms.