Flow-mediated growth of an aquatic herbivore

Herbivorous macroinvertebrates make up a large fraction of secondary production in wetlands, but little is known about how water flow affects herbivorous macroinvertebrate production. Reintroducing measurable water flow (1–5 cm/s) to the oligotrophic (phosphorus-limited) Everglades has the potential to improve herbivorous macroinvertebrate production by providing a constant low supply of phosphorus (P) to periphyton and improving food quality. This study investigated potential effects of flow-mediated nutrient loading on growth rates of herbivorous grazers, juvenile apple snails (Pomacea maculata). Periphyton was grown on standard substrates, within a landscape-scale flow addition experiment, in two sloughs that received elevated velocities (3–5 cm/s) and two control sloughs. The flowing sloughs produced periphyton with greater biomass, higher concentrations of nutrients, and lower C:P ratios. Snails, in a laboratory setting, gained more than 3.7-fold greater total mass when fed periphyton from flowing sloughs than snails fed periphyton from control sloughs. Water column nutrients were slightly elevated in flowing sloughs, but the amount could not fully explain differences in periphyton nutrients or snail growth. Increasing flow above background conditions improved food quality, which subsequently increased growth rates. Restoring flow has the potential to increase nutrient accessibility that could enhance food webs, but additional study will be needed to determine whether increased growth rates translate into increased standing stocks.