The project demonstrated that macroalgae play a significant and previously under-recognised role in supporting Greenshell mussel (Perna canaliculus) productivity within integrated aquaculture systems. Stable isotope analysis and field studies showed that macroalgal detritus can contribute up to approximately 58% of the nutritional input supporting mussel growth, particularly during cooler months when phytoplankton availability is limited. While phytoplankton remains the preferred food source during summer, macroalgae act as an important seasonal nutritional subsidy that can stabilise mussel growth rates across the year. The research also confirmed that the presence of live macroalgae can improve water chemistry by increasing pH levels, which benefits shell formation in juvenile mussels and potentially reduces energetic costs associated with calcification.

The research identified substantial variation between macroalgal species in their suitability for co-culture. Differences in palatability, decomposition rates, and biochemical composition influence both mussel nutrition and carbon sequestration potential. Species with lower levels of defensive phenolic compounds were generally more digestible and nutritionally valuable to mussels. Conversely, species with higher levels of these compounds resisted grazing and microbial degradation, increasing the likelihood that their organic matter could persist in sediments or be transported to deep water, contributing to long-term carbon storage. These findings highlight the potential for selective breeding or targeted species selection to optimise macroalgae for both aquaculture productivity and environmental outcomes.

Technological advances were another major outcome of the project. Researchers successfully developed hatchery and transplantation techniques for key kelp species, including Ecklonia radiata and Macrocystis pyrifera, enabling large-scale propagation and deployment onto mussel longlines. The research also showed that integrated kelp-mussel systems can reduce nitrogen emissions from shellfish farms and provide habitat and feeding opportunities for fish species. Collectively, the findings demonstrate that co-culturing macroalgae with mussels has strong potential to enhance aquaculture sustainability, support emerging seaweed industries, and contribute to blue-carbon mitigation strategies in New Zealand.