Subtidal Mussel Restoration: A Tool for Recovering Ecosystem Services

Abstract

In an attempt to address globally relevant environmental crises, the United Nations declared 2021-2030 as “the UN decade on Ecosystem Restoration” (UN Resolution 73/284). Restoration initiatives are especially timely for coastal ecosystems which deliver a myriad of benefits to mankind yet are subject to multiple anthropogenic stressors with cumulative effects. As the combined effects of these stressors have led to concurrent declines in global shellfish ecosystems, there is growing interest in the ability of bivalve restoration projects to revitalise the coastal ecosystems shellfish historically inhabited. In response to anthropogenically-induced population collapse, coastal restoration utilising endemic green-lipped mussels (Perna canaliculus) is currently underway in New Zealand, with ecosystem service provision considered a primary justification for the continuation and upscaling of restoration projects. However, there is little information available to quantify service value associated with mussel restoration efforts, nor is there information regarding how ecological functions and processes underpinning these services might differ with contrasting environmental properties exhibited at various restoration locations. This thesis investigates the role of mussel restoration in recovering ecosystem functionality and service value relevant to the biodiversity, eutrophication, and climate crises (chapters 2, 3, and 4 respectively). Through a variety of mechanisms, mussel beds are shown to generally increase species richness and abundance of associated organisms, which in turn influence regulating services (nitrogen and carbon cycling) explored in later data chapters. I show that enhanced nitrogen removal rates observed in mussel beds are consistent despite patchiness in restored beds, highlighting the upscaling-role of mussels in seafloor biogeochemistry. Finally, I take an ecosystem-based approach to create a carbon budget for restored mussel bed systems, discussing implications for coastal carbon cycling through space and time. Throughout the thesis I consistently demonstrate that the magnitude and extent of service provision varies as a result of environmental conditions experienced; therefore, restoration location should be crucially considered for its impact on the generation and delivery of ecosystem services.