Long-term study reveals top-down effect of crabs on a California salt marsh

Consumers can structure plant communities, and may function as keystone species or ecosystem engineers. In salt marshes, the prevailing paradigm has shifted in recent decades from nearly complete focus on bottom-up processes to inclusion of top-down effects. Although the number of studies investigating top-down control continues to climb, few experiments span multiple years, so temporal variability in or long-term impacts of consumers have not been well characterized. In addition, while top-down control has been found to be common in Western and Eastern Atlantic and Western Pacific salt marshes, our study is one of the first to experimentally consider top-down control of salt marsh plants in the Eastern Pacific. We conducted a five-year field experiment along eroding creekbank edges of a California salt marsh in which we manipulated densities of the shore crab, Pachygrapsus crassipes, and tracked marsh responses over time. Our results demonstrate that, through both consumption and engin...