Forage Fish and the Ocean Carbon Cycle

Ocean ecosystems play a major role in the global carbon cycle by transporting vast quantities of atmospheric carbon dioxide to the deep ocean via a process called the Biological Carbon Pump. Tiny plants known as phytoplankton convert sunlight and carbon dioxide into biomass before being consumed by small animals called zooplankton. In turn, zooplankton can be consumed by fish who then release carbon and nitrogen as dissolved organic matter or through the production of fast-sinking fecal pellets. Fish have long been overlooked in biological carbon pump research, but recent findings suggest that fish might contribute 10–20% of total carbon export, and even more in some locations. Despite these initial estimates, the role of fish in the biological pump is still poorly resolved. For example, parameters as simple (but crucially important!) as fecal pellet sinking rates are still not entirely understood.

This project will produce some of the foundational data required to estimate the impact of forage fish on carbon storage both locally and in the global ocean. Part of this work consists of at-sea incubations of live fish to study their waste production rates and the properties of their fecal pellets — for example their sinking speed and carbon and nitrogen content. We then use the information produced from these experiments to predict the effects of this waste production on the marine ecosystem and ocean carbon storage, considering historical, present-day, and future ecosystem states. This work will help us better quantify the value of marine ecosystems in terms of carbon storage potential, as well as the role of upper ocean ecosystems in delivering vital nutrients to sea-floor communities.