Investigating the stress response of blue mussels to heat tolerance in a Northeast Atlantic hybrid zone

Abstract

Heatwaves and rising sea surface temperatures are expected to increasingly affect mussel aquaculture. Beyond shaping species distributions, warming may alter the organisms’ cellular stress responses (CSR), with consequences for survival, growth, and recruitment. Many studies have focused on thermal stress in pure Mytilus spp., with comparatively less attention given to admixed genotypes. This study examined the effects of repeated thermal stress on blue mussels from an Irish hybrid zone, simulating projected Northeast Atlantic heatwaves. Pure Mytilus edulis , M. galloprovincialis , and admixed mussels were exposed to a two-week heat-stress regime (13–22 °C) in a controlled environment. Expression of heat shock protein genes ( hsp24, hsc71, hsp90 ) and superoxide dismutase ( sod ) was quantified via Reverse-Transcription quantitative PCR (RT-qPCR) across four timepoints (before exposure, 24 h, 4 and 7 days after heat exposure) and modelled using Linear Mixed-effect Models (LMMs). Among genes, hsp24 showed significant induction, with time having a significant effect on expression. Before heat exposure, no significant differences were observed among controls, treatments, and genotypes. The first acute heat stress (24 h after exposure) induced the greatest response in hsp24 , while at subsequent time points, expression decreased. This study provides new insight into the thermal sensitivity of pure and admixed blue mussels, highlighting the importance of temporal dynamics in shaping heat stress responses. Further work is needed to understand how hybrid zones and farmed stocks respond to warming, supporting aquaculture management in a changing ocean.