RESUMEN
Transport out of the water is one of the most challenging events for juvenile Perna canaliculus and can be a highly inefficient process, with many juveniles subsequently being lost following extended periods of emersion. Hardening techniques offer a possible method for reducing transport-related stress. In this study, different hardening treatments (short, long and intermittent sub-lethal emersion) were used to prepare ~1.2 mm P.canaliculus for transport (20 h) and subsequent reoxygenation stress during re-immersion (i.e., recovery). The oxidative stress responses, resettlement behaviour, respiration rates and survival of the mussels after transport and during recovery were all assessed. Short emersion (1 h) as a hardening treatment prior to transport did not cause major stress to the mussels, which maintained respiration at control levels, showed significantly stimulated antioxidant defences during recovery, showed greater resettlement behaviour and remained viable after 24 h of recovery. In comparison, the long and intermittent emersion treatments negatively impacted oxidative stress responses and affected the viability of the mussels after 24 h of recovery. This study showed that exposing juvenile P.canaliculus to a mild stress prior to transport may stimulate protective mechanisms, therefore eliciting a hardening response, but care must be taken to avoid overstressing the mussels. Improving the management of stress during the transport of juvenile mussels may be key to minimising mussel losses and increasing harvest production, and biomarkers associated with oxidative stress/antioxidant metabolism could be valuable tools to ensure emersion hardening does not overstress the mussels and reduce survival.
RESUMEN
Increasing seawater temperatures coupled with more intense and frequent heatwaves pose an increasing threat to marine species. In this study, the New Zealand green-lipped mussel, Perna canaliculus, was used to investigate the effect of genetics and ontogeny on thermal resilience. The culturally and economically significant mussel P. canaliculus (Gmelin, 1971) has been selectively-bred in New Zealand for two decades, making it a unique biological resource to investigate genetic interactions in a temperate bivalve species. Six selectively-bred full sibling families and four different ages, from early juveniles (6, 8, 10 weeks post-fertilisation) to sub-adults (52 weeks post-fertilisation), were used for experimentation. At each age, each family was exposed to a three-hour heat challenge, followed by recovery, and survival assessments. The shell lengths of live and dead juvenile mussels were also measured. Gill tissue samples from sub-adults were collected after the thermal challenge to quantify the 70 kDa heat shock protein gene (hsp70). Results showed that genetics, ontogeny and size influence thermal resilience in P. canaliculus, with LT50 values ranging between 31.3 and 34.4 °C for all studied families and ages. Juveniles showed greater thermotolerance compared to sub-adults, while the largest individuals within each family/age class tended to be more heat sensitive than their siblings. Sub-adults differentially upregulated hsp70 in a pattern that correlated with net family survival following heat challenge, reinforcing the perceived role of inducible HSP70 protein in molluscs. This study provides insights into the complex interactions of age and genotype in determining heat tolerance of a key mussel species. As marine temperatures increase, equally complex selection pressure responses may therefore occur. Future research should focus on transcriptomic and genomic approaches for key species such as P. canaliculus to further understand and predict the effect of genetic variation and ontogeny on their survival in the context of climate change.