Postdoctoral Fellowship: OCE-PRF: What drives mesopelagic biomass in the California Current

The mesopelagic zone is a region of the ocean between 200 and 1000 m deep, often defined by its distance and distinctness from the sunlit surface waters above. In reality, the marine organisms inhabiting these depths are not isolated from changing conditions in the upper ocean, as they perform daily vertical movements to feed near the surface. Few long-term observations of mesopelagic communities exist worldwide, making it difficult to determine how vulnerable they may be to global climate change.

This project uses a combination of nets, sound (acoustics) and marine ecosystem models to explore the oceanographic and ecological factors affecting the abundance and distribution of mesopelagic organisms in the California Current Ecosystem. By exploring how past changes in community composition, horizontal movement, habitat compression and advective processes have led to changes in mesopelagic abundance along the US west coast, we can better understand how this ecosystem may be impacted by future climate conditions.

In addition to supporting a postdoctoral scholar, this award will provide mentorship and training to students who would not normally have access to deep-sea research. We will mentor students on how to use and understand fisheries acoustics through the SIO JT-SURF program, curated labs in undergraduate courses, and opportunities to gain firsthand experience with acoustics at sea.

We will also collaborate with a scientific illustrator to broaden scientific literacy and raise public awareness of mesopelagic communities as a critical component of healthy marine ecosystems.

Although mesopelagic science is advancing quickly, and we now recognize the contributions of mesopelagic communities to global biodiversity, biomass, and carbon export, mesopelagic organisms are still poorly understood due to the difficulty of sampling at great depths. This project adds to a growing knowledge by investigating which oceanographic conditions and processes have driven past changes in the composition and horizontal distribution of the mesopelagic community of the California Current.

First, we will develop a classification system to improve the taxonomic resolution of acoustic surveys, by combining acoustic transects with discrete depth sampling with nets to 2000 m. Second, we will use a coupled physical, biogeochemical regional ocean model to examine the oceanographic processes linked to observed changes in mesopelagic backscatter.

Mesopelagic animals provide food for many economically important and protected species (e.g., swordfish and dolphins), and their vertical movements are important for transferring carbon from the surface to the deep ocean. As mesopelagic habitats are projected to shoal by the end of the century, this work is timely for understanding potentially unexpected changes in deep-sea communities in response to warming ocean conditions, and for advancing our understanding of an integral, but poorly understudied component of the broader California Current Ecosystem.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.