Coastal erosion is one of the most pressing environmental challenges many coastal communities face. While salt marsh ecosystems are highly valued for many ecosystem services, marsh erosion has been accelerated worldwide due to human-driven environmental change. The impacts of nutrient loading on marsh erosion have been experimentally demonstrated in east coast marshes. The hypothesized mechanism is that when nutrients are no longer limiting, marsh plants shift tissue allocation from belowground to roots that both acquire nitrogen and stabilize the marsh soils to aboveground leaves that gather more light. Another increasingly recognized cause of marsh erosion is grazer-driven marsh vegetation loss. Studies on multiple continents have shown that marsh grazers, including many burrowing crabs, can strongly suppress marsh vegetation and kill all vegetation when their abundance increases in the absence of predator control. Whether predator recovery, one of my major research areas outlined above may help halt marsh erosion due to runaway grazer-driven vegetation losses, however, is unknown.
On the west coast of the U.S., where trophic feedbacks are thought to be weak, marshes are experiencing high levels of loss due to intense edge erosion (0.5-1.5 m/yr)1 without regrowth. As these are highly eutrophic estuaries, intense nutrient loading is purported to be a major driving factor in marsh loss. In those west coast marshes, however, we have observed high densities (50-100 burrows/m2) of burrowing crabs on marsh edges. These crabs actively eat marsh plants and their roots, likely contributing to bank erosion as well. In collaboration with my post doc (Brent Hughes) and incoming graduate student Leo Chan Gaskins, we will experimentally investigate the extent to which top-predator expansion (sea otters) can halt marsh erosion through trophic control of runaway grazer impacts. We predict that although nutrient loading and outbreak of burrowing crabs have increased coastal erosion in Elkhorn Slough marshes, top-predator recovery due to recent predator conservation efforts will significantly help halt marsh erosion. This work will be ground breaking in that it will be the first to experimentally test how top predators can change the geomorphology of an ecosystem.