Many fishes shelter in mangrove habitats by day and forage mostly in seagrass beds by night. This pattern of diel habitat use has been attributed to a predator avoidance strategy, whereby predation risk is reduced by alternating between the cover afforded by prop-roots during the day and darkness at night. We employed a series of diel tethering experiments in Biscayne Bay (Florida, USA) to empirically examine whether relative predation pressure on fishes is lower at night than during the day and to compare relative predation pressure on fishes at different distances from the mangroveseagrass ecotone. Pinfish Lagodon rhomboides ranging from 10 to 17 cm in total length were tethered during day and night at 10, 50, and 110 m from the mangrove-seagrass ecotone. Pinfish removal rates at night were twice as high as during the day, which contradicts the idea that darkness provides 'cover' during nocturnal foraging in seagrass. Predation losses were highest nearest the mangrove edge and decreased with increasing distance from shore. Our results agree with those of other tethering studies that marine ecotones, or transition zones between refuges and feeding sites, can be areas of high predation pressure for fishes. KEY WORDS: Predators · Edge effects · Proximity gradient · Shark · Snapper · Porgy · Grunt Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 401: [259][260][261][262][263][264][265][266][267] 2010 tor access (Shulman 1985, Blaber 2007, Rypel et al. 2007). Most previous studies, which have been primarily diurnal, have consistently reported fish densities to be higher nearest the mangroves compared to offshore (e.g. Jelbart et al. 2007, Newman et al. 2007, Unsworth et al. 2008. However, direct field-based evidence evaluating how predation risk varies spatially in seagrass beds in relation to mangrove proximity is lacking.Ecotones, or habitat transition zones, are recognized as hunting corridors for predators in a variety of systems (Decamps & Naiman 1988, Ries & Sisk 2004. Organisms are likely at highest risk from predation when crossing ecotones between sheltered and feeding patches, due to the high concentration of individuals in refuges and predictability of their foraging movements. For example, off the coast of South Africa, hunting white sharks (Carcharodon carcharias) patrol fur seal (Arctocephalus pusillus pusillus) refuge entry and exit points in attempts to ambush seals as they leave for, and return from, foraging (Martin et al. 2005, Hammerschlag et al. 2006, Martin et al. 2009). Although previous studies in a variety of habitats (e.g. reefs, Shulman 1985) have reported predation pressure to be high near ecotones, or habitat edges, this has not been previously reported in mangroveseagrass habitats and results of most published diurnal fish abundance surveys indicate highest fish densities nearest the mangroves (Jelbart et al. 2007, Newman et al. 2007, Unsworth et al. 2008.Recently, Hammerschlag & Serafy (in press) examined nocturnal abundance ...

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