The last several decades of research has revealed a startling trend in the world-wide decline of both coastal ecosystems (seagrass, kelp, marsh, and corals) and marine top predators. This has resulted in the near collapse of many coastal fisheries and loss of ecosystem services, such as carbon sequestration, shoreline protection, and nursery grounds. However, decades of policy and management actions protecting marine predators, such as the Marine Life Protection Act, Endangered Species Act, Marine Mammal Protection Act , and the Fur Seal Act has enabled the recovery of certain top predator species along the northeast Pacific coast.
My research focuses on the recovery of sea otters (Enhydra lutris) and its unexpected effects on nearshore ecosystems. My colleagues and I are assessing the role of sea otters in habitats beyond the well-known kelp forest by looking at their expansion into other nearshore environments, such as seagrass and salt marshes. This research has demonstrated that sea otters are capable of generating trophic cascades in eelgrass (Zostera marina) beds through their predation on crabs. This trophic cascade benefits seagrass, even in the case of extreme nutrient loading:
The cartoon above shows how sea otters benefit seagrass in a eutrophic environment through their predation on crabs. This predation frees invertebrate mesograzers from predation by crabs, thus enabling them to efficiently remove harmful epiphytes from seagrass. Below is a video that shows summertime conditions in an estuary with and without sea otters (click on the image to play):
Hughes, B.B., R. Eby, E. Van Dyke, M.T. Tinker, C. Marks, K.S. Johnson, K. Wasson. 2013. Recovery of a top predator mediates negative eutrophic effects on seagrass. Proceedings of the National Academy of Sciences USA 110:1513-1518.
Hughes, B.B., S.C. Lummis, S.C. Anderson, K.J. Kroeker. 2017. Unexpected resilience of a seagrass system exposed to global stressors. In press. Global Change Biology.
Eby, R., R.S. Scoles, B.B. Hughes, K. Wasson. 2017. Serendipity in a salt marsh: detecting frequent sea otter haul outs in a marsh ecosystem. In press. Ecology.