Crab Burrowing Limits Surface Litter Accumulation in a Temperate Salt Marsh: Implications for Ecosystem Functioning and Connectivity
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Burial of aboveground plant litter by animals reduces the amount available for surface transport and places it into a different environment, affecting decomposition rates and fluxes of organic matter to adjacent ecosystems. Here we show that in a Southwestern Atlantic salt marsh the burrowing crab Neohelice granulata buries aboveground plant litter at rates (0.5–8 g m−2 day−1) comparable to those of litter production (3 g m−2 day−1). Buried litter has a low probability (0.6%) of returning to the marsh surface. The formation of burrow excavation mounds on the marsh surface is responsible for most litter burial, whereas litter trapped in burrows was an order of magnitude lower than rates of burial under excavation mounds. Crab exclusion markedly increased surface litter accumulation (3.5-fold in just 21 days). Tides with the potential to transport significant amounts of surface litter are infrequent; hence, most litter is buried before it can be transported elsewhere or decomposes on the surface. Crab litter burial can account for the observed low levels of surface litter accumulation in this ecosystem and likely drives organic matter transformation and export. The impacts of ecosystem engineering by this crab species are therefore substantial and comparable in magnitude to the large effects found for tropical crabs and other litter-burying organisms, such as anecic earthworms.
Keywordsburrow excavation litter burial Neohelice granulata ecosystem engineering ecosystem export internal ecosystem functioning
We thank Martín Bruschetti, Andrés Rodríguez, and Federico Vera for field assistance, Marcelo Kittlein for statistical advice, and Oscar Iribarne for laboratory space and facilities at Universidad Nacional de Mar del Plata during the execution of this project. We are also indebted to Mónica Fiore (Servicio de Hidrografía Naval, Argentina) for tidal measurements from Mar del Plata port. This paper benefited from the comments made by the Subject-Matter Editor, Dr. Tim Essington, and two anonymous reviewers. Research was supported by the Andrew W. Mellon Foundation and the Cary Institute of Ecosystem Studies (CGJ, JLG, PMG and SEGF). JLG and PDR were supported by scholarships from CONICET at the time of this study. This is a contribution to the programs of GrIETA and the Cary Institute of Ecosystem Studies.
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