The impact of epifaunal predation on the structure of macroinfaunal invertebrate communities of tidal saltmarsh creeks

Abstract

The impact of epibenthic predators foraging on macroinfaunal communities was analysed in Great Sippewissett salt marsh (MA, U.S.A.) by installing experimental cages in the most productive sediments of the marsh (77 g dry weight m-2 year-1). The most productive macroinfaunal species in these sediments were Marenzelleria viridis (43.1 g dry weight m-2 year-1) Heteromastus filiformis (13.7 g dry weight m-2 year-1) and Neanthes arenaceodonta (7.6 g dry weight m-2 year-1). Macroinfaunal densities peaked in June following the spring recruitment. Density and biomass inside the cages were significantly higher during the growing season, however, density declined in July and August following the seasonal cycle observed outside cages, while biomass did not suffer this decline. The absence of epibenthic predators favored growth and accumulation of larger organisms, especially M. viridis, and included higher presence of predaceous infauna (Glycera americana, Neanthes succinea, Neanthes virens, Eteone heteropoda and Nemerteans). At the end of the experiment, there was 22.2 g dry weight m-2 more macroinfaunal biomass in the complete cages than in ambient sediments. The absence of epibenthic predators also increased secondary production; M. viridis doubled production in the sediments inside cages compared with outside cages. The most common benthic predaceous fishes in the marsh were the killifishes, Fundulus heteroclitus and Fundulus majalis, and some seasonal invasive fishes (Gasterosteus aculeatus, Tautoga onivis, Centropristes striatus and Pleuronectes americanus). While invasive fishes preyed mainly on benthic invertebrates and grew faster, resident fishes shifted their diets through the season. The values of macroinfaunal secondary production obtained in these sediments can support the energy requirements of the predators of the marsh; in this way the pulse of secondary production created by the macroinfaunal populations travels up the saltmarsh food web.