An example of multi-habitat restoration: Conceptual assessment of benefits from merging shellfish-reef and boulder-reef restorations

Abstract

Multi-habitat restoration should be considered for conservation of habitat-types that are ecologically-related and regularly co-occur. Multi-habitat restoration has been used to a limited extent for marine habitats including oysters, mangroves and seagrass. Recent increases in research and understanding of shellfish-reefs and boulder/cobble-reefs means they should likewise be considered for integrated restoration. Importantly, boulders have recently been used as the foundation for several large-scale oyster-reef restorations. These would benefit from improved recognition that multiple distinct habitat-types are involved each associated with distinct knowledge pools. These habitat-types mostly have similar restoration objectives, they often co-occur pre-disturbance, and they share varied taxa. These linkages mean that opportunities may be missed if restorations are only considered separately in contexts where an integrated approach is feasible; restoration of one habitat may benefit from concurrent restoration of the other and the sum of benefits from integration may outweigh the sum from restorations done separately. Here, I discuss concepts concerning five potential synergies: 1) boulders provide natural hard-substrata that initiates shellfish recruitment, 2) boulders produce beneficial hydrological heterogeneity, increasing recruitment of some shellfish species, 3) shellfish generate self-sustaining supplies of novel hard-substrata habitat used by boulder/cobble species thus expanding the original restoration site footprint, 4) large shellfish populations strengthen valuable ecological functions in boulder habitats, and 5) boulders and shells together increase overall diversity of available hard-substrata types, and thus of associated specialist species. Not only restoration outcomes, but also objectives and planning can be improved by integrating knowledge from both habitat-types to encompass these five synergies.