Co‐restoring keystone predators and foundation species to recover a coastal wetland

Abstract

Abstract Achieving global targets for ecosystem restoration necessitates the development of effective restoration approaches. Current restoration approaches focus primarily on mitigating abiotic stresses or supplementing propagules to restore foundation species that support associated species by ‘engineering’ local habitats. Although keystone predators can strongly affect foundation species in natural ecosystems via trophic cascades and are often diminished in degraded ecosystems, they are traditionally neglected in efforts to restore foundation species. Here, we investigated how a keystone predator (Scylla serrata) might affect the restoration of a foundational plant (Scirpus mariqueter) in a degraded salt marsh. In a series of restoration experiments, we examined the effects of proximity to existing Scylla burrows, as well reintroducing Scylla, on the establishment of planted Scirpus in restoration areas. Furthermore, we tested if Scylla affected Scirpus via non‐consumptive effects in experiments that controlled Scylla's consumption of grazers. We found that planted Scirpus suffered less grazing and achieved higher density in areas closer to existing Scylla burrows where Scylla predation on grazers was stronger. Consistently, reintroduction of Scylla reduced grazing on Scirpus and increased its density by 360%. These positive effects of Scylla on Scirpus were driven by consumptive effects that reduced the abundance of grazers and by non‐consumptive effects that inhibited the herbivory by grazers. Synthesis and applications. These results demonstrate that incorporation of keystone predators, including both their consumptive and non‐consumptive effects, into restoration designs can greatly enhance the restoration of foundation species. Our study thus highlights the value of co‐restoring keystone predators and foundation species. Given that predators are depleted in many ecosystems, this co‐restoration approach may be broadly applicable.