XVI International Botanical Congess

We evaluated the effect of plants on the habitat selection by the crab Chasmagnathus granulata on SW Atlantic salt marsh by experiments and sampling. Botanical richness was related positively to the depth of the freatic nap as well as to the distance to the streamside border. However, it related negatively regarding the crab density. Plants benefit crabs colonization and their permanence by buffering some physical variables. The temperature in covered areas is up to ten degrees Celsius lower than uncovered areas. These uncovered areas show lower sunlight penetration. Soil surface humidity is higher in these vegetated areas than in others. Plant aboveground structures permit crab permanence after settlement, but below ground structures are not needed for those purposes. Our results also show that any inert aboveground structure give way to settlement and permanence of adult crabs by buffering the same physical variables that plants buffer. The density of crabs was higher in the high marsh covered areas. Crabs avoid high-uncovered areas. There is no difference in the abundance of crabs under the two dominant species (Spartina sp. and Salicornia sp.). This evidence suggests that plants indirectly drive habitat selection and permanence of adult crabs in the high marsh.