Benthic Versus Planktonic Foundations of Three Lake Superior Coastal Wetland Food Webs

Abstract

The structure of aquatic food webs can provide information on system function, trophic dynamics and, potentially, responses to anthropogenic stressors. Stable isotope analyses in a Lake Superior coastal wetland (Allouez Bay, WI, USA) revealed that the food web was based upon carbon fixed by phytoplankton. We report analyses of two Lake Superior coastal wetland food webs not based upon plankton, indicating that Allouez Bay is not the prototype. In Lost Creek and West Fish Creek wetlands (WI, USA), upper trophic levels appear to be supported by benthic, rather than planktonic, food web pathways. Also, zooplankton in Lost Creek and West Fish Creek wetlands are enriched in 13C relative to periphyton, rather than 13C-depleted as reported in most other systems. This appears to be a consequence of zooplankton feeding on detrital seston that is 13C-enriched relative to phytoplankton. We suggest possible causes for the observed differences in food web structure among these wetlands, including hydrologic differences among the systems, and responses to nutrient enrichment among the dominant forms of primary producers, similar to those described in lakes.