Quantifying reactions of copepods to marine snow through image analysis

Aggregations of sinking phytoplankton and other organic matter in the ocean, often referred to as marine snow, are extremely prevalent and are therefore a very crucial part of the biological pump which transports carbon from surface waters to the deep ocean. Often these marine snow particles do not sink uninterrupted through the water column due to interactions with organisms such as copepods. Previous field and laboratory studies have demonstrated that marine snow is likely an important food source for some copepods, including the species Calanus pacificus. Ingestion of marine snow by copepods may result in fragmenting marine snow particles, which can alter the rate of carbon transport throughout the ocean. However, little is known about how these interactions mechanistically take place between copepods and the particles they fragment. In this study, we used high-resolution imaging to directly observe interactions between tethered copepods and sinking marine snow particles. Through the analysis of these images, we were able to quantify the reaction of copepods in relation to the location of the sinking particle. In addition, we measured gut content as a proxy for ingestion rate, which allowed us to determine how much marine snow each copepod consumed. Future work will allow us to track the size and speed of particles before and after fragmentation to further explore the impact of these interactions on the transport of carbon in the ocean.