Considering the use of subadult and juvenile mussels for mussel reef restoration

Abstract

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 importance of stock selection for improving transplantation efficiency

“…Previous work found that loose, unprotected subadult and juvenile mussels disappear within 1 week of being placed at experimental sites (Alder et al 2020). To improve initial postdeployment survival, the mussels in this study were provided a clumping period prior to deployment.…”

“…The restoration of biogenic habitat depends on careful consideration of larval, seed, and adult stock sources (Schulte et al 2009; Fitzsimons et al 2019). For restoration that relies on translocations of populations from aquaculture, careful stock selection that accounts for growth conditions and size may improve survival and restoration efficiency (Alder et al 2020) while avoiding the use of costly engineering interventions (Capelle et al 2019; Schotanus et al 2020 a , 2020 b ). In this study, variations in post‐translocation survival were closely related to stock source and differences observed in the formation of protective clumps as explained by two aspects of clumping behavior (P:A ratio, D ).…”

“…The high survival of aquaculture basket mussels suggests that modifications to aquaculture growing conditions can be made to raise mussels well‐suited to overcome the pressures that currently limit the use of subadult mussels for restoration (Alder et al 2020). While mussels raised intertidally or to larger SLs on aquaculture long‐lines (i.e.…”

“…For field comparisons of survival, mussels from each population were partitioned into seven groups of 200 mussels each (1,400 total per population) and held in individual plastic baskets (6 mm mesh; 732 × 270 × 140 mm, L × W × H ) that remained submerged in holding systems until translocation to the seafloor. The quantity of mussels used in field comparisons was considered a sufficient representation of the numbers observed in naturally occurring clumps of mussels (blue mussels—Snover & Commito 1998; green‐lipped mussels—Alder et al 2020). Note that groups refer to the sets of 200 mussels ( n = 7) from each population ( n = 5), while clumps refer to aggregates of ≥2 mussels attached by byssus threads (Côté & Jelnikar 1999) occurring within each group.…”

“…At small (m 2 ) scales, long‐line juvenile and subadult mussel losses can be mitigated by engineering measures such as predator exclusion cages (e.g. green‐lipped mussels; Alder et al 2020) or breakwaters that lower environmental stressors to promote organization into reef structures (e.g. for intertidal blue mussels; Capelle et al 2019; Schotanus et al 2020 a , 2020 b ).…”