Background
Greenshell™ mussels (Perna canaliculus) underpin New Zealand's aquaculture sector, yet production remains highly inefficient. Nearly 400 billion spat are harvested annually to yield only 1.5 billion harvestable mussels (Skelton et al., 2022). A major driver of this inefficiency is the extremely small size of spat used for seeding, typically just 0.5 to 1 mm in shell length, which makes them highly vulnerable to post-seeding losses. Rearing spat to larger sizes in nursery systems could greatly improve retention, reduce spat wastage, and increase farm productivity. The first step to developing scalable, predictive nursery systems is to determine the relative importance of different dietary pools to spat growth. This would enable nursery managers to monitor food availability and better predict nursery performance. In this study, spat were reared in an upwelling nursery system to quantify the relative depletion of phytoplankton, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and particulate organic matter (POM), providing an initial assessment of the relative importance of different dietary pools.
Methods
Spat were reared in a land-based upwelling nursery system supplied with raw seawater from an adjacent bay in the Marlborough Sounds. Water samples were collected from the system inflow and outflow to quantify changes in phytoplankton, DOC, DON, and POM.
Results and Discussion
Phytoplankton showed the greatest and most consistent depletion across sampling periods (peaking at 21.1% of the available pool), indicating it was the primary dietary resource for spat. POM was depleted to a lesser extent, while DOC and DON showed low or inconsistent depletion, suggesting a comparatively minor nutritional role. This study provides an initial step toward identifying the key dietary pools supporting Greenshell™ mussel spat in nursery systems. These results identify the dietary pools most likely to influence nursery performance. Future work will quantify the assimilation efficiency and growth value of each pool, enabling the development of biologically meaningful food metrics for predictive nursery management.
Acknowledgments
This work was funded by an MBIE Endeavour Research Programme, UOA2515 "Reducing spat losses to grow New Zealand's Greenshell mussel sector"
References
Skelton, B. M., South, P. M., & Jeffs, A. G. (2022). Inefficiency of conversion of seed into market-ready mussels in New Zealand's Greenshell™ mussel (Perna canaliculus) industry. Aquaculture, 560, 738584.