Spatial and temporal movement of the lined shore crab Pachygrapsus crassipes in salt marshes and its utility as an indicator of habitat condition

The utility of the lined shore crab Pachygrapsus crassipes as an indicator of small-scale variation in the condition of salt marshes was determined by conducting detailed mark-recapture studies of the spatial and temporal patterns of movement in 2 marshes in northern and southern California, and by conducting a stable isotope study along a nutrient gradient at one of the marshes. Crabs (1158) were captured from creek bank and vegetated marsh habitats, tagged, and released. Most crabs were recaptured in the same trap where they were originally tagged, and on average, they traveled less than 5 m from the site of first capture. The mean distance traveled did not increase significantly with the time between captures. A high percentage of crabs (62.1%) tagged near the creek bank remained there; fewer tagged crabs moved between the creek bank and the marsh plain (18.2%) or remained on the marsh plain (12.6%). Crabs moved least along creek banks and farthest when crossing creeks, although few of them did the latter (6.2%). During spring tides, crabs moved from tidal creeks onto the marsh plain. The nitrogen isotope data mirrored the gradient in nutrient input, supporting the conclusion that P. crassipes remained and fed within a localized area. Thus, the lined shore crab can serve as an indicator of small-scale differences in contaminant exposure. Furthermore, semiterrestrial species that are readily sampled and move little are abundant around the world, making them ideal indicators of habitat condition. © Inter-Research 2006