Forecasting the impact of marine heat waves on farmed bivalves Nodipecten nodosus and Magallana gigas

Marine heat waves are considered a threat to the cultivation of commercially important species because exposure to thermal stress may lead to mass mortalities of organisms. Investigating the upper thermal limits of marine species and their capacity for shifting these limits can contribute to securing the sustainability of aquaculture activities as exposure to heat extremes is increasing in frequency. The scallop Nodipecten nodosus and oyster Magallana [Crassostrea] gigas are two bivalve species commercially farmed in Brazil and production of spat is undertaken mainly at two hatcheries located in different regions subjected to distinct climate and seawater temperature conditions over the year. This study investigated the upper thermal tolerance of populations of N. nodosus and M. gigas sourced from temperate and tropical farming areas. Groups of N. nodosus and M. gigas farmed under warmer temperature regimes exhibited lower mortality rates when exposed to elevated temperatures compared to groups sourced from cooler waters and consequently displayed higher values of lethal temperature 50 (LT50). N. nodosus exhibited superior thermal tolerance than was previously known, however, commercial cultivation of this species is still at risk of mass mortalities depending on the duration and intensity of forecasted heat waves in both cultivation regions. M. gigas showed a high capacity to endure acute thermal stress at the resting stage of the reproductive cycle. To enhance the aquaculture sector's resilience to climate change, we recommend the development of cultivation methods that account for marine and atmospheric heat wave events, alongside continuous monitoring of abiotic factors at farming sites.