Degradation of Surf-Fish Foraging Habitat Driven by Persistent Sedimentological Modifications Caused by Beach Nourishment

Abstract

Novel wave-tank mesocosms allowed hydrodynamically realistic tests of how sediment modifications affect feeding by a surf fish, Florida pompano, Trachinotus carolinus (Linnaeus, 1766). Pompano demonstrated visually based selection, preferentially preying on bean clams, Donax variabilis Say, 1822, colored in contrast with background. Pompano often took shell into their mouths instead of live bean clams. Sediments of nourished Bogue Banks (North Carolina) beaches exhibited >2.5-yr persistence of elevated coarse shell content at levels that suppressed pompano feeding in wave tanks. Elevated turbidity 4-8 mo after nourishment indicated that wave-induced erosion of buried fine sediments in sacrificial beach fill resulted in repeated turbidity events, reaching levels that in wave tanks reduced pompano feeding on Donax and mole crabs, Emerita talpoida (Say, 1817). Burial speeds of these prey in the beach swash zone were progressively reduced by increasing shell concentrations. Reduced burial rates reduce feeding opportunity and expose these mobile invertebrates to greater risk of wave transport out of the swash-zone habitat. Sampling six beaches revealed that density of Donax decreased linearly with increasing sediment size and shell concentration. Beyond the immediate mass mortality of invertebrate prey caused by >1 m of sediment deposition during beach filling, coarse shell fragments and other large particles persist as a press disturbance for years after the nourishment ends, and elevated silts/clays can become resuspended by erosive wind events in repeated pulse disturbances for at least months afterward, in each case reflecting demonstrable long-term degradation of sandy-beach foraging habitat for surf fish.