Evaluating the Growth and Survival of Diploid and Triploid Blue Mussel ( <i>Mytilus edulis</i> ) Larvae From Different Sources Reared at Constant and Fluctuating Thermal Regimes

Farming triploid bivalves has gained favor due to their enhanced growth rate and effective sterility; however, they may exhibit lower thermal tolerance, a concern due to climate change. Environmental conditions influence ectotherm performance, resulting in natural intraspecific variation across geographic regions through local adaptation, developmental plasticity, or transgenerational phenotypic plasticity. Notably, blue mussels in particular locations in Nova Scotia (NS) experience elevated summer temperatures and exhibit a higher thermal tolerance relative to mussels from Prince Edward Island (PE), where temperatures are comparatively lower. This study aimed to assess the performance (growth and survival) of Mytilus edulis larvae using a fully factorial design between (1) source (NS vs. PE); (2) ploidy (diploid vs. triploid); and (3) thermal regimes (constant vs. fluctuating). Larvae were reared under a hatchery standard, constant 18°C or a semidiurnal fluctuating thermal regime of 16–20°C. After fertilization, eggs were either subjected to hydrostatic pressure shock to induce triploidy or placed directly into rearing treatments. Triploidy was confirmed using flow cytometry, and survival and growth were measured until settlement. This experiment found that (i) PE larvae had a larger mean length compared to NS larvae at 22 days postfertilization (dpf); (ii) PE larvae exhibited a higher triploid percentage; (iii) triploid treatments had lower survival and comparable mean lengths to diploid treatments; (iv) the fluctuating regime had no effect on survival or growth, but it diminished both the mean shell length advantage and triploid percentage of PE larvae; and (v) triploid percentage decreased under the fluctuating thermal regime. Future studies should investigate the mechanisms that explain differential performance across larval sources and explore effects in other life stages. These insights can serve as the foundation for producing climate‐resilient blue mussels, thereby promoting the ecological and economic sustainability of the aquaculture industry.