The burrowing crab Neohelice granulata affects the root strategies of the cordgrass Spartina densiflora in SW Atlantic salt marshes

Salt marshes are among the most productive systems of the world, with plant primary production limited by soil oxygen deficiency and nutrient availability. Nevertheless, root adaptations to anoxia and nutrient acquisition are different and often incompatible. The SW Atlantic salt marshes are characterized by high densities of the deep (up to 1 m) burrowing crab Neohelice granulata (Dana, 1851) that may change soil physical and chemical characteristics by burrow construction. In this work, we experimentally evaluated the hypothesis that crab burrowing can enhance soil oxygenation, causing changes in Spartina densiflora Brongniart below ground tissues from structures adapted to anoxia to systems adapted for nutrient acquisition. This response, in turn, would enhance plant productivity. Results from field observations show that oxygen availability is higher in zones with high burrow densities. As burrow densities increased, the plant root distribution changed from shallow (associated to low oxygen availability) to deeper and vertically homogeneous, with a positive correlation between burrow density and plant aboveground biomass. Experimental exclusion of crabs shows that they induce changes of root strategies from anoxia toleration to nutrient efficient acquisition, with increasing plant productivity. The invasive success that this plant shows in other parts of the world is likely to be due to their ability to tolerate harsh environmental conditions. Our results suggest that the morphological plasticity of S. densiflora is also important in their native zone given the characteristics of their specific habitat.