Cage Protection Duration Reveals Critical Window of Opportunity for the Successful Attachment of Translocated Adult Mussels in a Semi‐exposed Intertidal Ecosystem

ABSTRACT Green‐lipped mussels ( Perna canaliculus ), like other reef building bivalves, are ecosystem engineers that hold considerable importance commercially and culturally. However, natural beds of this endemic species in Aotearoa New Zealand have been decimated through overharvesting and recovery has been almost non‐existent. For restoration purposes, mussels are typically sourced from subtidal aquaculture farms requiring time to allow for successful attachment. This is particularly challenging in exposed environments where dislodgement risk is high and limited research exists. The aim of this field experiment was to investigate the use of cages for different durations to protect and contain adult mussels translocated to a semi‐exposed intertidal site to assess attachment success and survival. Farm‐supplied mussels ( n = 20 per plot) were translocated to plots with no cages, partial cages or full cages for three different durations (i.e., 2, 15 or 29 days; n = 3 plots per treatment). All plots were assessed at 2‐ and 14‐days post cage removal (total experimental period of 46 days). Condition of mussels was also assessed at the start and end of the experiment. The duration of cage containment was shown to be a key factor in attachment success and survival. Results indicated that the longest protection period significantly improved mussel attachment, thereby improving settlement success. A protection period of only two days resulted in ∼98% loss of mussels after 14 days, whereas 29 days of cage protection reduced losses to ∼10%. The condition of mussels at the end of the experiment, however, was reduced compared to deployment. These findings highlight the promising value of using temporary protection during the initial attachment phase of translocated adult mussels and the importance of allowing for an adequate window of opportunity to establish strong byssal attachments to the available substrates. This study provides important insights for future restoration of mussels in semi‐exposed intertidal environments.