Relative predation risk for fishes along a subtropical mangrove-seagrass ecotone

Many fishes shelter in mangrove habitats by clay 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 mangrove seagrass 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 clay, 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.