Intraguild Predation Is Insufficiently Mitigated by Complex‐Structured Aquatic Vegetation

ABSTRACT Intraguild predation (IGP) occurs when one predator species consumes another species with whom it also competes for shared prey. IGP is widely believed to reduce prey suppression. In terrestrial ecosystems, structurally complex habitats may lessen IGP by offering refuge to intermediate predators. However, whether submerged macrophytes in shallow lakes could mitigate such antagonistic interactions remains largely unexplored. We examined the interactive impact of two aquatic predators, fish ( Pelteobagrus fulvidraco , intraguild predator) and shrimp ( Exopalaemon modestus , intraguild prey), on the biomass and assimilation of zooplankton prey in vegetation‐sparse and vegetation‐dense habitats in outdoor mesocosms. Relative to the shrimp‐alone treatment, the presence of both predators resulted in a higher average zooplankton biomass in both simple and complex vegetation habitats. This suggests that IGP between the two predator species alleviated predation pressure on the zooplankton community when compared to the shrimp‐alone mesocosms. However, no significant predator‐macrophyte interactions were detected, suggesting that the strength of IGP was not significantly affected by habitat vegetation complexity. Evidence from zooplankton dietary markers (fatty acids) and associated carbon stable isotopes further substantiated that vegetation complexity did not significantly affect the assimilation of zooplankton by predators. Additionally, vegetation complexity had no significant effect on chlorophyll a concentrations. The results demonstrate that the strength of IGP was not substantially influenced by habitat vegetation complexity. Our findings have implications for food webs and predator–prey dynamics within aquatic systems. Thus, when implementing biomanipulation efforts aimed at combating eutrophication by enhancing herbivory on phytoplankton and promoting the resurgence of submerged macrophytes, both the quantity and diversity of predator assemblages, as well as the scale effects of submerged macrophytes, should be considered.