Burrowing And Bioturation By Fiddler Crabs In The Florida Keys PDF Download

Positive rather than negative species interactions dominate in stressful environments like tidal marshes. Fiddler crabs have been shown to ameliorate environmental stress and increase primary productivity through their burrowing behavior. Most notably, bioturbation may facilitate growth of tidal marsh plants by altering soil oxygen concentration, decomposition rates, and soil drainage. In turn, plants provide protection from the elements, refuge from predators and roots provide structural support for burrows in soft substrate. However, dense vegetation may limit the fiddler crab's ability to maneuver on the surface and burrow. Similarly, there may be a threshold where fiddler crab activity becomes destructive to plant growth instead of facilitative. Relatively few fiddler crab and plant interaction studies have been conducted on the Gulf Coast compared to Atlantic Coast. Gulf Coast tidal marshes have distinct climate, dominant vegetation zones and dominant fiddler crab species, and consequently it is likely that community dynamics will differ from Atlantic Coast tidal marshes. To explore interactions between Gulf Coast fiddler crabs and tidal marsh plants, I conducted a seasonal fiddler crab habitat survey and a fiddler crab enclosure study. Both studies were conducted at Grand Bay National Estuarine Research Reserve in Mississippi, across four dominant tidal marsh vegetation zones (salt marsh, brackish marsh, fresh marsh and salt panne). Fiddler crab burrows and associated vegetation were randomly surveyed across the vegetation zones to determine fiddler crab burrow density and habitat preferences. Fiddler crab enclosures were established across the four vegetation zones. Enclosures provided a method to test impacts of fiddler crab burrowing on soil and plant parameters as well as to survey fiddler crab populations. Results of the habitat survey indicated that fiddler crabs utilized all four vegetation zones, but burrow density was statistically higher in the fresh marsh during winter compared to other zones. These results suggest that the fresh marsh may be important habitat for overwintering Gulf Coast fiddler crabs. Additionally, the fresh marsh was found to host higher fiddler crab species diversity and a more balanced sex ratio compared to other zones. The enclosure study established that fiddler crab activity had negligible impacts on plant growth in the salt and fresh marsh yet influenced plant growth in the brackish marsh (positively) and salt panne (negatively). The brackish marsh and salt panne are habitats of intermediate environmental stress for plants and fiddler crabs. Brackish marsh is more frequently inundated than the salt panne and hence bioturbation is likely to be more beneficial in the brackish marsh. Furthermore, brackish marsh below-ground structure is substantial and fiddler crab burrow density was low relative to the salt panne. My work indicates that vegetation abundance and fiddler crab burrow density may balance environmental stresses in tidal marshes and influence nature of fiddler crab and plant interactions.