The effect of marine snow particle distribution on copepod behavior

Marine snow is a major component of the biological pump, through which carbon is exported to the deep ocean. The sinking of marine snow can be disrupted by organisms that ingest or breakup the falling aggregates. Previous studies have found that zooplankton ingest these aggregates, which may have important impacts on planktonic food web dynamics and carbon export. Marine snow can have patchy distributions, occurring in layers, which may further impact interactions with zooplankton; however, no experimental study has looked specifically at how the presence of a marine snow layer could affect zooplankton foraging behavior. In this study we examined how the distribution of marine snow particles affected copepod foraging and behavior, specifically with regard to their swimming patterns.

We conducted a series of experiments in which copepods of the species Calanus pacificus were exposed to three different feeding environments: a layer of marine snow, a homogenous distribution of marine snow, and a control treatment without marine snow. Copepod behavior was recorded with two cameras that were set up perpendicular to one another, imaging the sides of the tank. MATLAB was used to reconstruct 3D copepod tracks, allowing us to calculate copepod location, velocity, and turning rate throughout the experiments. We observed that copepods performed a spiraling swimming behavior when they were above marine snow particles, potentially in response to chemical plumes from the sinking marine snow aggregates. We saw less of this spiraling behavior in the layer treatment, which potentially suggests that the slowed velocity of these particles in the layer may reduce their chemical signature and make them less detectable to copepods. In addition, we will interpret our results within the context of concurrent measurements of copepod gut content to examine how marine snow distribution can not only affect copepod behavior, but also have implications for larger scale trophic dynamics.