New Zealand’s aquaculture industry is at increasing risk from intense marine heatwaves which threaten the productivity and sustainability of marine farms, emphasizing the need for targeted genetic solutions. Perna canaliculus (Greenshell mussels; GSM) are an endemic New Zealand mussel of cultural and commercial importance that have been selectively bred since 2002. This well-established family-based breeding programme provides an opportunity to breed for thermal tolerance and improve survival and growth during periods of elevated temperature.
In collaboration with industry, we have developed a reliable and repeatable survival challenge to compare thermal tolerance of different mussel families, with survival assessed as the number of days to death at 26°C (maximum sea surface temperature in summer). We have used this method to assess heat tolerance in adult families of different ages (from 1-3 yrs). Results to date show that heat tolerance in GSM is moderately heritable (h2 = 0.27-0.54), suggesting that if thermal tolerance is included in a selection index, there is adequate genetic variation to enable genetic improvement of thermal tolerance in this GSM population. We have also found that in juvenile and sub-adult mussels (aged 6-52 weeks post-fertilisation), both genetics and ontogeny strongly influence thermal resilience when these mussels are exposed to an acute heat challenge.
In parallel to GSM survival challenges, we have measured gene expression levels of the 70 kDa heat shock protein (Hsp70), immune responses, the transcriptome and the microbiome of mussel haemolymph or gill samples from selected families. This helps us to understand how the different families respond physiologically to heat stress, and gives us the opportunity to identify and compare biomarkers of heat stress in families with high and low heat tolerance.
These results highlight the complex interactions between genetics, age and size which all determine heat tolerance in GSM. Our findings indicate that selective breeding for heat tolerance is promising in GSM, and is likely to be a key tool used for climate change adaptation into the future.