Assessing the potential to restore green-lipped mussels in Pelorus Sound/Te Hoiere, New Zealand

Abstract

The global loss of marine ecosystem engineering species, such as reef-building bivalves, has led to widespread calls for restoration. Restoration of reef-building bivalves, such as oysters and mussels, can be hindered by multiple factors including selection of inappropriate locations and deployment methods, particularly in a new restoration area. The research presented in this thesis aimed to examine the potential to restore green-lipped mussels, Perna canaliculus, in Pelorus Sound/Te Hoiere, New Zealand, in an effort to understand how to overcome barriers to natural mussel recovery in this area. With three experimental deployments of mussels comprising four field experiments, this research addresses the questions of; 1) whether seafloor habitats throughout the inner-Pelorus Sound/Te Hoiere are suitable for adult mussel survival, 2) if restored mussel reefs promote biodiversity across three different faunal classifications and how that differs among different benthic environments within the first year post-restoration, 3) if the provision of shell substrate aids in the establishment of adult mussels in different benthic environments, and 4) whether smaller mussels can be utilized for restoration in intertidal (exposed at low tide) and subtidal (5-7 m) environments. The three experimental mussel deployments resulted in high survival ~75% in the subtidal environments over 1-2 years, while the major influence impacting survival at that depth appeared to be sea star predation. A year after the addition of mussels to the seafloor there was a general reduction of infaunal abundance and biodiversity, but an increase in epifaunal and pelagic faunal abundances, specifically from those species that benefit from benthic habitat complexity and an increase in food availability. The provision of shell substrate did not appear to have an influence on adult mussel establishment; however, the added substrate may have positive environmental influences that need further examination. Smaller mussel survival in the subtidal and intertidal locations were similar to larger mussels, indicating they can be used for more cost-efficient mussel restoration. Although the mussel survival was high across the three deployments, no juvenile mussel recruits were ever observed in the restored mussel reefs, despite mussel settlement occurring on settlement collectors placed on the reefs. The lack of juvenile mussel recruitment into the restored mussel reefs and the presence of predator sea stars in some locations will hinder long-term mussel restoration in the area. Further investigation is needed to overcome juvenile recruitment bottlenecks to effectively restore the green-lipped mussel population in Pelorus Sound/Te Hoiere, New Zealand. Overall, the findings of the research presented in this thesis do indicate that the low-intertidal and subtidal habitats in Pelorus Sound/Te Hoiere remain suitable for supporting green-lipped mussels.