Impacts of marine heat extremes on bivalves

Abstract

As the global ocean continues to experience the consequences of an increase in the frequency and intensity of heat waves, the trend is expected to persist into the 21st century, with a projected tripling of heat waves by 2040. This phenomenon poses a significant threat to marine ecosystems and the survival of marine organisms, including the ecologically and economically vital bivalves. Bivalves are vulnerable to harm from heat stress at various levels of biological organization, and their growth can be negatively impacted by high temperatures, potentially leading to mass mortalities and posing a threat to ecosystem quality and food security. In light of these concerns, this review aims to provide a comprehensive examination of the effects of heat stress on bivalves. It summarizes the physiological and biochemical changes that bivalves undergo in response to extreme heat events and offers an overview of the strategies they employ to mitigate their impacts. A better understanding of the underlying mechanisms of bivalve responses to heat stress is crucial in order to fully appreciate the impact of these events on these organisms. This review synthesizes the current knowledge on heat stress in bivalves and highlights the importance of further research in this area. By providing a comprehensive overview of the physiological and biochemical changes that bivalves experience during heat stress and the strategies they use to mitigate its impact, this review aims to support the development of more effective approaches to minimize heat stress in bivalves.

Marine diseases and the Anthropocene: Understanding microbial pathogenesis in a rapidly changing world

“…The increased exposure of an organism to environmental stressors, either in intensity or frequency, is generally regarded to reduce the ability of that organism to respond to a pathogen. For example, thermal stress associated with extreme heatwaves can dampen molecular and phenotypic immune processes in bivalves, echinoderms and macroalgae (Campbell et al, 2011;Masanja et al, 2023;Murano et al, 2023), while exposure to pollutants such as ammonia or heavy metals can compromise the integrity of the shrimp intestinal mucosa rendering it susceptible to infection (Duan et al, 2018(Duan et al, , 2021. However, there remains a paucity of detailed molecular knowledge regarding the immune physiology of many marine organisms and hence the mechanisms by which stress may render them susceptible to infection are not known.…”

Differential responses of selectively bred mussels (Perna canaliculus) to heat stress—survival, immunology, gene expression and microbiome diversity

“…The effects of climate change on aquaculture can be positive, neutral or negative, depending on the region and the species being farmed ( Maulu et al, 2021 ). Inshore operations are often more vulnerable to coastal ocean acidification and heatwaves, which has resulted in numerous mass mortality events of farmed bivalves, especially during summer ( Masanja et al, 2023 ).…”

“…Traditionally, these desirable traits have primarily related to variables such as shell color for bivalves, fast growth, disease resistance or feed efficiency ( Gjedrem et al, 2012 ; Hollenbeck and Johnston, 2018 ). As the risks associated with climate change are now well documented, selective breeding for environmental resilience (e.g., thermal tolerance) has been identified as a key trait to include in selective breeding programmes ( Pernet and Browman, 2021 ; Liu et al, 2022 ; Masanja et al, 2023 ). The use of selectively bred mussels in transcriptomic and microbiome studies also allows assessment of their response to different stressors while controlling for genetic variation, which can often confound such studies.…”

Hard clam resilience to marine heatwaves in the face of climate change

“…Throughout the past 20 years, MHWs have become more severe, recurrent, and longer in coastal ecosystems, especially attacking intertidal zones that support a very productive coastal environment (Masanja et al, 2023;Whalen et al, 2023). The thermal conditions in intertidal regions, specifically in subtidal zones, undergo substantial changes that surpass the fluctuations observed in ocean water temperatures, both in terms of amplitude and variability (Dong et al, 2022).…”

“…Despite the increasing prevalence of MHWs at an unprecedented rate, there remains significant uncertainty surrounding the response of economically and ecologically relevant organisms to the intensification of MHWs (Garrabou et al, 2022;Smith et al, 2023). MHWs may cause profound impacts at various levels of biological organization on marine bivalves, including hindering metabolism, reducing energy reserves, impairing reproduction, and triggering dysbiosis at the molecular level (Masanja et al, 2023). Encompassing population feedback down to the molecular level can hence provide a more accurate assessment of the effects of MHWs on marine bivalves and their ecosystems.…”