The role of refiltration on suspension feeder carrying capacity and coexistence with zooplankton

Increasing man-made substrates in aquatic environments leads to changes in food-web pathways, notably enhancing pathways linked to suspension feeding. However, increasing such pathways imposes a competitive pressure on zooplankton. Zooplankton play important roles in aquatic ecosystems, typically contributing to marine secondary production, nutrient cycling, and vertical mass transfers. Predicting the impacts of man-made substrates, therefore, requires understanding the mechanisms that determine coexistence among these two groups. We present a simplified Dynamic Energy Budget (DEB)-based ecosystem model that incorporates properties intended to enhance spatial coexistence. The model contains two realistic properties linked to suspension feeding: a density-dependent interference in suspension feeding, and an emerging concentration gradient above the sessile suspension feeders. To map conditions at which coexistence was possible, we performed bifurcation analyses with respect to the parameters controlling suspension feeding and spatial processes. Finally, we determined which DEB parameters had the strongest influence on whether the dynamics of this ecosystem model stabilize. The concentration gradient played a large role on equilibrium time-scales, while the density-dependent interference in suspension feeding enabled coexistence by modulating suspension feeder carrying capacity. Furthermore, the amount of density-dependent interference at which the dynamics of the ecosystem model stabilize was affected by zooplankton consumption and maintenance processes. In summary, spatial mechanisms associated to suspension feeding inherently allow zooplankton and suspension feeders to coexist.