Bioturbating bivalves show potential to bioremediate degraded soft sediments by restoring ecosystem function

Abstract Introduction Natural recovery of disturbed marine ecosystems can take years, mainly because long‐lived, functionally important species are lost. To regain ecosystem services, the focus of estuarine restoration is shifting from biodiversity metrics to functional restoration. Objectives In a disturbance‐recovery experiment, we investigated the potential of two functionally different bivalve species for restoring soft‐sediment ecosystem functioning by assessing proxies related to sediment properties, ecosystem productivity, and nutrient cycling. Methods Clams (porewater pressurizing Macomona liliana , 200 ind./m 2 and bioturbating Austrovenus stutchburyi , 800 ind./m 2 ) were added to experimentally defaunated sediments within Tauranga Harbor, New Zealand. Treatments consisted of no bivalve addition, single species additions, combined addition, and an unmanipulated ambient/control. Measures of sediment properties, ecosystem functioning, and bivalve survival were taken 20 (3 weeks), 81 (3 months), and 389 days (1 year) post‐bivalve addition. Results The addition of A. stutchburyi can facilitate recovery of proxies for ecosystem function similar to ambient levels compared to unaided recovery. Austrovenus stutchburyi aided recovery by reducing sediment mud content (2–3%), enhancing sediment oxygen consumption (16–30%), and increasing ammonium flux (40‐fold) compared to no addition treatments, even after 389 days. Macomona liliana had limited influence on the assessed ecosystem functions, and co‐addition of species identified no additional effects. Although survival of translocated A. stutchburyi was low (16%) after 1 year, measures of recovery were enhanced in addition treatments. Conclusions Hence, using bioturbating bivalves for estuarine bioremediation to restore ecosystem functioning shows promise, provided the limits of degradation are within the species' capability to survive.