Mechanism by which coarse woody debris affects predation and community structure in Chesapeake Bay W. Christopher Long ⁎, Andrew J. Sellers 1 , Anson H. Hines Smithsonian Environmental Research Center, P.O. Box 28, Edgewater, MD 21037, USA abstract article info Article history: Received 7 March 2013 Received in revised form 21 May 2013 Accepted 24 May 2013 Available online 29 June 2013 Keywords: Blue crab Coarse woody debris Community structure Grass shrimp Mummichog Predation Coarse woody debris (CWD) provides a structured habitat in aquatic systems. It is associated with a higher abundance, diversity, and productivity of aquatic animals and can provide a shelter from physical stressors and predation. We investigated the effects of CWD on predation risk and community structure in two field exper- iments in the Rhode River, Chesapeake Bay. In the first experiment we assessed the effects of the orientation (horizontal or vertical) and complexity (simple or crossed) of CWD, and in the second experiment we investigated the effects of interstitial space (ISS). We measured predation risk in a tethering experiment for three species in each experiment: juvenile blue crab, Callinectes sapidus; mummichog (a type of killifish), Fundulus heteroclitus; and grass shrimp, Palaemonetes pugio. These three species are common in nearshore Chesapeake Bay habitats but differ in their size and habitat use, allowing for a holistic examination of the function of CWD. At the end of the experiments, the benthic community inhabiting the CWD was sampled. By interpreting the community data in light of the predation experiments we were able to examine how the structural characteristics of the CWD af- fected predation to shape the benthic community. In the first experiment, lowest predation was experienced by blue crabs at the treatments with high complexity at the sediment surface, by mummichogs at all CWD treatments relative to control plots, and by grass shrimp in horizontally oriented treatments. In the second experiment, lowest predation was experienced by blue crabs at moderate to high ISSs, by mummichogs at intermediate ISSs, and by grass shrimp at low and high ISSs. Predation rates for each experimental species could be predicted by the size of the prey, and by both the size of their predators and the size of species that prey on the predators relative to the ISS of the structure. Community structure differed among treatments in both experiments and appeared to be driven primarily by predation risk; species whose predators were in high abundance in a treatment were less abundant themselves. This work demonstrates the importance of CWD and of wooded shorelines as impor- tant habitat for both economically and ecologically important species. It also highlights the importance of top-down forcing in the small scale community dynamics of these near-shore habitats. Published by Elsevier B.V. 1. Introduction Coarse woody debris (CWD) is an important structural feature of aquatic systems in freshwater (Angermeier and Karr, 1984; Benke et al., 1985; Lehtinen et al., 1997) estuarine (Everett and Ruiz, 1993), and marine (Storry et al., 2006) environments. Coarse woody debris is associated with higher abundance and diversity of organisms (Angermeier and Karr, 1984; Brooks et al., 2004; Gerhard and Reich, 2000; Helmus and Sass, 2008), higher productivity of both inverte- brates and fish (Benke et al., 1985), lower predation rates (Everett and Ruiz, 1993), and reduced intraspecific aggression (Sundbaum and Naslund, 1998), and can alter the physical environment by changing characteristics such as water flow and sediment deposition (Bilby and Likens, 1980; Brooks et al., 2004). Though CWD and other structured habitats can protect organisms from physical stressors (Beck, 1998) or increase food availability either by being a food source itself or by pro- viding a growing surface for biofilm (Storry et al., 2006), perhaps its most important role is that of a predation refuge (Everett and Ruiz, 1993; Hrodey and Sutton, 2008). The orientation and complexity of CWD can have a strong influence on its function (Newbrey et al., 2005; O'Connor, 1991; Schneider and Winemiller, 2008). The orientation of CWD affects how it interacts with the physical environment (e.g. how it alters water flow and sedi- ment depositions) and thus its function as habitat (O'Connor, 1991). The structural complexity of CWD can increase the surface area avail- able for colonization and predation refuge (Bartholomew et al., 2000; Johnson et al., 1988; Schneider and Winemiller, 2008). More complex CWD is associated with higher densities of macroinvertebrates and fish (Newbrey et al., 2005; Schneider and Winemiller, 2008), likely Journal of Experimental Marine Biology and Ecology 446 (2013) 297–305 ⁎ Corresponding author at: Kodiak Laboratory, Resource Assessment and Conservation Engineering Division, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA, 301 Research Ct., Kodiak, AK 99615, USA. Tel.: +1 907 481 1715; fax: +1 907 481 1701. E-mail address: chris.long@noaa.gov (W.C. Long). 1 Current address: McGill University, 845 Sherbrooke Street West, Montreal, Quebec H3A 0G4, Canada. 0022-0981/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.jembe.2013.05.021 Contents lists available at SciVerse ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe