THE IMPACT OF EPIFAUNAL PREDATION ON THE STRUCTURE OF MACROINFAUNAL INVERTEBRATE COMMUNITIES OF TIDAL SALT-MARSH CREEKS

The impact of epibenthic predators foraging on macroinfaunal communiti es was analysed in Great Sippewissett salt marsh (MA, U.S.A.) by insta lling experimental cages in the most productive sediments of the marsh (77 g dry weight m(-2) year(-1)). The most productive macroinfaunal s pecies in these sediments were Marenzelleria viridis (43.1 g dry weigh t m(-2) year(-1)) Heteromastus filiformis (13.7 g dry weight m(-2) yea r(-1)) and Neanthes arenaceodonta (7.6 g dry weight year year m(-2) ye ar(-1)). Macroinfaunal densities peaked in June following the spring r ecruitment. Density and biomass inside the cages were significantly hi gher during the growing season, however, density declined in July and August following the seasonal cycle observed outside cages, while biom ass did not suffer this decline. The absence of epibenthic predators f avored growth and accumulation of larger organisms, especially M. viri dis, and included higher presence of predaceous infauna (Glycera ameri cana, Neanthes succinea, Neanthes virens, Eteone heteropoda and Nemert eans). 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 sedi ments. The absence of epibenthic predators also increased secondary pr oduction; 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, T autoga onitis, Centropristes striatus and Pleuronectes americanus). Wh ile invasive fishes preyed mainly on benthic invertebrates and grew fa ster, resident fishes shifted their diets through the season. The valu es of macroinfaunal secondary production obtained in these sediments c an support the energy requirements of the predators of the marsh; in t his way the pulse of secondary production created by the macroinfaunal populations travels up the saltmarsh food web. (C) 1998 Academic Pres s Limited.