XVI International Botanical Congess

We are investigating the effect of the crab Chasmagnathus granulata on a mature and on regrowing Spartina-saltmarsh areas by using a phenometric non destructive method. Fire and cattle grazing are two of the perturbations that regularly kill mature plants. In addition, they are important agents for structuring communities. We work on two different regrowing stages of grass. Forty days after the beginning of the experiment, crabs decreased the standing crop biomass, reduced leafy areas and number of leaves per shoot of regrowing plants. Crabs increased the number of dead stems, but did not affect the number of newly emerging stems. Regarding mature plants, crabs did not affect any variables. Results reported that crabs showed the most negative effects concerning only regrowing stages of Spartina plants. The trophic flexibility of the burrowing crab combined with its high endemism, may allow them to have a strong localized effect on salt marsh production. More specifically, C. granulata could affect cordgrass production by herbivore on new shoots. This study is still underway in order to assess the crab impact on cordgrass population dynamics over the long term.