Impact of Macroconsumers on Leaf Breakdown and Detritivores in Wetlands on a Southeastern US Coastal Plain Floodplain during Drought

Abstract

Interactions between macroconsumers (predators and large omnivores) and detritus breakdown on river floodplains are poorly understood, yet important to ecosystem function. We evaluated the impact of macroconsumers on leaf breakdown, macroinvertebrate abundance and biomass, and fungal biomass on a river floodplain using exclosures in 6 wetlands during a severe drought during which the floodplain was disconnected from the river. Sweetgum (Liquidambar styraciflua) leaves were held in both mesh bags and in leaf packs within each exclosure. After 301 days, breakdown rates (k) were slow and did not significantly differ between treatments. Fungal biomass and total macroinvertebrate abundance and biomass also did not significantly differ between treatments. Collector-gatherers were significantly more abundant in treatments open to macroconsumers in mesh bags. Shredders had significantly higher biomass in packs held in exclosures closed to macroconsumers, but were rare. A subsequent exclosure experiment in one flooded wetland mimicked stream-floodplain connectivity despite drought. Pre-conditioned leaves in mesh bags open to macroconsumers had significantly faster breakdown than those closed to macroconsumers. Abundance of total macroinvertebrates, scrapers and predators were higher in treatments open to macroconsumers. These results indicate that the role of macroconsumers on floodplains varies depending on river connectivity and water availability.