Widespread resource extraction and habitat degradation have severely reduced functionally important subtidal mussel reefs globally. While methods for restoring oyster reefs are becoming increasingly well-established, the development of techniques for the effective restoration of mussel reefs remain in their infancy and face biological and logistical challenges. This study investigated the potential use of subadult and juvenile green-lipped mussels (Perna canaliculus) for mussel reef restoration with the aim of understanding factors related to subadult and juvenile mussel survival after transfer to the seafloor. Small-scale (m 2) field experiments were conducted subtidally in a New Zealand harbor to assess subadult and juvenile mussel survival after translocation to soft-sediment seafloor, the efficacy of biodegradable substrate to support reef development, and whether juvenile mussel survival was related to changes in seeding density. Results demonstrated survival of cultured subadult and juvenile mussels after transfer to soft-sediment seafloor only when completely protected from mobile predators. Attachment to biodegradable substrate alone was insufficient to prevent the loss of cultured juvenile mussels, while 80% of wild subadult mussels survived translocation to the seafloor without predator protection-indicating a certain level of resilience. Changes in seeding density failed to prevent loss of cultured juvenile mussels. This study supports further consideration for incorporating cultured subadult and juvenile mussels into restoration, provided subadult and juvenile mussels can be protected until they become established as adults.

The restoration of shellfish reefs to soft‐sediment environments often relies on the translocation of donor stock, typically from aquaculture, to the seafloor. In New Zealand, subadult green‐lipped mussels (Perna canaliculus) grown on subtidal aquaculture long‐lines are being considered over adult conspecifics to increase restoration efficiency but are currently limited by predation and hydrodynamic dislodgment following transfer to the seabed. In this study, the survival of subadult mussels from five different sources representing a range of growth conditions (i.e. subtidal aquaculture long‐lines 1 and 2, subtidal shellfish aquaculture baskets 1, wild intertidal reefs 1 and 2) were compared across separate translocations (1 and 2) to see if careful consideration of stock source could improve subadult mussel survival following transfer to the seafloor. Mussel morphology (shell strength, attachment thread structure) and clumping behavior (perimeter:area ratios, clump densities, clump complexity) were compared among populations to explain relationships among prior stock growth conditions, mussel size, and survival. Following experimental translocations, high survival (>90%) was closely related to decreases in perimeter:area ratios of mussel clumps and increases in clump complexity. High survival groups of mussels were selected from stock with high shell compression strength (subtidal aquaculture long‐line 2, 95.5% survival), greater attachment thread number and thickness (aquaculture basket 1, 92.3% survival), or some combination of the two (wild intertidal reef 2, 99.3% survival). This study supports further consideration for incorporating subadult mussels into restoration provided they are selected from sources that produce individuals with the resistant characteristics outlined in this study.

The loss of newly translocated species directly contributes to low rates of reintroduction success in both terrestrial and aquatic ecosystems. In this study, experimental reintroductions of green-lipped mussels Perna canaliculus into a shallow coastal habitat were conducted across 5 week-long experimental translocations within a 10 mo period (April 2021-January 2022) to relate temporal variations in predator abundance, predator size, and environmental parameters (water temperature, rainfall, days before/after full moon, turbidity, wind speed, wind direction) to variations in mussel survival. Predator counts from timelapse camera images gathered over the first 4 d after each deployment were used as a proxy for potential predator pressure. Timelapse images (n = 8561) allowed for a census of 2371 individuals from 10 different mobile species, 5 of which were known bivalve predators (Australasian snapper, New Zealand eagle ray, rig shark, octopus, and an unidentifiable ray species), with Australasian snapper contributing to 98% of overall species counts. At the end of the study, mean mussel survival ranged from 0 ± 0 SE% to 56 ± 8 SE% and was best predicted by changes in turbidity and the total number of predators among deployments (R2 = 0.445). Patterns in predator abundance were best explained by time of year and did not share strong correlations among environmental parameters (rho = 0.015). These results suggest that planning deployments of mussels for cooler times of the year when water clarity is high and predator abundance is low may substantially increase immediate survivorship of translocated mussels and improve reintroduction success.