Decadal shifts in a salt marsh macroinfaunal community in response to sustained long-term experimental nutrient enrichment

The effect of nutrient enrichment on benthic macroinfauna was examined in a long-term experiment that increased food supply in a macroinfaunal community inhabiting salt marsh muddy tidal creeks in Great Sippewissett Marsh (MA, USA). After 15 years of nutrient addition, macrofaunal density and production were higher in fertilized compared to control creeks, primarily because of the response of oligochaete species. Although mean annual total secondary production was higher in fertilized creeks (9.4 g dry weight . m(-2). y(-1)) than in control creeks (6 g dry weight . m(-2). y(-1)), P:B ratios for the key species were similar in both creeks, ranging between 2 and 3. Sustained enrichment shifted species dominance in fertilized creeks. Two oligochaete species, the naidid Paranais litoralis (Muller, 1784), and the tubificid Monopylephorus evertus Baker and Brinkhurst, 1981, became the dominant species responding to the sustained enhancement of food resources by the fertilizer addition. In non-fertilized creeks, the polychaete Streblospio benedicti Webster, 1879, remained the dominant species throughout the 15 year duration of the experiment. The fertilizer has stimulated growth of different oligochaete populations that are able to exploit different resources through the year (bottom-up regulation). During summer, the bottom-up effect of fertilization disappears, and predation controls invertebrate abundance (top-down regulation).