Exposure of Greenshell Mussel Spat ( Perna canaliculus ) to Stressors for Producing Single‐Spat From Collector Ropes

ABSTRACT Nursery culture can improve the efficiency of mussel aquaculture by reducing the high losses of spat and overcoming inconsistencies in wild‐spat supplies. The success of nursery systems depends on the availability of unattached single or singulated spat, which requires the separation of spat from their associated settlement substrates (i.e., singulation). This study investigated whether sub‐lethal environmental stressors could facilitate the singulation of Greenshell mussels ( Perna canaliculus ) spat from their attachment to collector ropes. Segments of spat‐collector ropes were exposed to stressors consisting of either high (45 ppt) or low (25 ppt) salinity for 2 h, periods of emersion (air exposure) for 2 or 4 h, or combinations of reduced aeration and limited food availability for 12 h. Spat singulated from the collector rope were returned to clean seawater and reared for 24 h, after which their survival rates were measured. The results indicated that up to 80% of spat could be singulated from the ropes after a 12 h exposure to seawater with no aeration and no food (i.e., NA‐NF). However, although survival rates following singulation ranged from 60% to 90% across treatments, overall recovery of viable, unattached spat was lower, reaching a maximum of 65% relative to the initial number of settled spat. Singulation efficacy was influenced by treatment and spat size, with smaller spat (< 3.5 mm) more easily singulated than larger ones (> 5 mm). Variations in the spat responses to the stressors indicate a need for further research to optimise singulation techniques and better understand the mechanisms driving the attachment and detachment responses in the mussel spat. Regardless, the study demonstrates that up to 65% of viable spat can be effectively removed from collector ropes using environmental stressors, making them readily available for rearing in nursery systems and reducing spat losses from production.