Fiddler crab burrowing aVects growth and production of the white mangrove (Laguncularia racemosa) in a restored Florida coastal marsh

Positive plant–animal interactions are important in community ecology, but relatively little attention has been paid to their eVect on the production of mangroves, dominant halophytic trees in tropical coastal marshes. Here, the role of Wddler crab (Uca spp.) burrowing on the growth and production of the white mangrove, Laguncularia racemosa (<2 years old), was examined in a restored marsh in Tampa Bay, Florida (27°41.65 N, 82°30.34 W) with manipulative experiments from June 2006 to May 2007. Fiddler crab burrowing signiWcantly increased mangrove height by 27%, trunk diameter by 25%, and leaf production by 15%, compared to mangroves in crab exclusion enclosures. Additionally, the exclusion of Wddler crabs signiWcantly increased interstitial water salinity from 32.4 to 44.2, and decreased the oxidation–reduction potential of the low organic sediments, but did not aVect soil pH or sulWde concentration. Mangrove height, trunk diameter, and leaf production along a transect that varied in crab burrow density were positively associated with the number of crab burrows. Further, the density of sympatric Spartina alterniXora shoots was positively correlated with crab burrow density along the transect. As in temperate marshes, Wddler crabs can have signiWcant ecological eVects on mangrove communities, serving as ecological engineers by modulating the amount of resources available to marsh plants, and by altering the physical, chemical, and biological state of these soft sediment communities. In restored coastal systems that typically have very poor sediment quality, techniques such as soil amendment could be used to facilitate a more natural interaction between crabs and mangroves in ecosystem development.