A quantitative analysis of marine heatwaves in response to rising sea surface temperature

Impact of marine heatwaves on Carcinus maenas crabs: Physiological and biochemical mechanisms of thermal stress resilience

Marine heatwaves (MHWs), characterized by prolonged periods of elevated sea temperatures, pose significant threats to marine ecosystems, particularly affecting the physiology and behavior of marine organisms, including crustaceans. This study investigates the physiological and biochemical responses of males and females of Carcinus maenas crabs, after an acute exposure to an MHW, focusing on energy metabolism, oxidative status, and potential neurotoxicity. Specimens were exposed to controlled laboratory conditions simulating a temperature increase from 17 °C to 23 °C, and responses were analyzed in gills and hepatopancreas. Results revealed sex-specific differences in thermal stress resilience, with males showing higher glycogen storage in gills after MHW exposure, while females exhibited a significant reduction in glycogen reserves and an increase in antioxidant enzyme activity. Superoxide dismutase and glutathione reductase activities were notably elevated in females subjected to MHW, suggesting a more robust antioxidant response to counteract oxidative stress. Additionally, acetylcholinesterase activity, an indicator of neurotoxicity, was significantly reduced in females post-MHW, hinting at potential neurotoxic effects. Despite these biochemical changes, lipid peroxidation levels remained stable across both sexes and tissues, indicating that short-term MHW exposure did not cause significant oxidative damage to cell membranes. This study highlights the importance of considering sex differences in assessing the impacts of climate change-induced stressors on marine organisms, as males and females display distinct metabolic and physiological strategies for coping with thermal stress.

Global warming drives a threefold increase in persistence and 1 °C rise in intensity of marine heatwaves

Marine heatwaves are extreme climatic events consisting of persistent periods of warm ocean waters that have profound impacts on marine life. These episodes are becoming more intense, longer, and more frequent in response to anthropogenic global warming. Here, we provide a comprehensive and quantitative assessment on the role of global warming on marine heatwaves. To do so, we construct a counterfactual version of observed global sea surface temperatures since 1940, corresponding to a stationary climate without the effect of long-term increasing global temperatures, and use it to calculate the contribution of global air temperature rise on the intensity and persistence of marine heatwaves. We determine that global warming is responsible for nearly half of these extreme events and that, on a global average, it has led to a three-fold increase in the number of days per year that the oceans experience extreme surface heat conditions. We also show that global warming is responsible for an increase of 1 °C in the maximum intensity of the events. Our findings highlight the detrimental role that human-induced global warming plays on marine heatwaves. This study supports the need for mitigation and adaptation strategies to address these threats to marine ecosystems.

Trends and variability of marine heatwaves in Portuguese coastal waters

Marine heatwaves (MHWs) represent a significant threat to marine ecosystems, particularly in vital fisheries regions such as the Portuguese coast. Understanding MHW dynamics at a finer spatial scale is essential for comprehending their impacts on the ecosystems. This study addresses this gap by analyzing historical MHW events from 1982 to 2023 and projecting future scenarios based on different greenhouse gas emission pathways. The primary objective is to characterize the spatiotemporal patterns of MHWs along the Portuguese coast and understand their temporal evolution. Using historical sea surface temperature (SST) data, MHW metrics were analyzed across various coastal regions. Future projections, utilizing Shared Socioeconomic Pathways (SSP) 245 and SSP 585, assessed changes in MHW frequency, duration, and intensity in the near future (2024-2060) and far future (2061-2100). Results indicate no significant spatial differences in average annual MHW metrics among study areas, but significant temporal variations were observed. The progression of MHW metrics is often more than twice as fast in the slopes and southern areas compared to the west shelf. Record-breaking MHW events in 2023 were consistent with global trends, highlighting a positive linear correlation between historical warming and increased MHW metrics. Projections under SSP 585 indicate a 2.5 to 4.5-fold increase in the annual number of MHW events, lasting 1 to 3 months, with nearly year-round MHW conditions by 2100, reaching peak intensities of 10.7 °C. These findings highlight the need for climate action to mitigate the impacts of intensified MHWs on coastal ecosystems. This research provides foundational insights into MHW dynamics along the Portuguese coast, laying the groundwork for future studies and highlighting the implications of climate change on marine environments.

Impact of Carbon and Nitrogen Assimilation in Sargassum fusiforme (Harvey) Setchell due to Marine Heatwave Under Global Warming

Because of the rising global temperatures, Sargassum fusiforme (Harvey) Setchell, a commercially valuable seaweed, has experienced reduced yield and quality due to high temperatures from marine heatwave events. However, the mechanisms underlying the effects of heatwave stress on S. fusiforme remain unclear. In this study, the mechanisms of heatwave stress on the carbon and nitrogen assimilation processes in S. fusiforme were analyzed. These results indicated that heatwave stress, especially at 30°C for 12 days, significantly increased the levels of hydrogen peroxide (83%), malondialdehyde (84.7%), and relative conductivity (16.5%) in algae, which suggested an increase in algal damage. Morphologically, heatwave stress damaged the thylakoid structure and reduced the photosynthetic efficiency of algae and accumulated NADPH, ATP, and α-ketoglutarate significantly, resulting in decreased content of mannitol, the photosynthetic product. Additionally, physiological and transcriptomic results revealed that heatwave stress inhibited the rate of nitrate absorption rate and the activities of the most enzymes associated with nitrogen accumulation, while significantly upregulating glutamate dehydrogenase (GDH), suggesting a crucial role for GDH in S. fusiforme's adaptation to heatwave stress. In terms of amino acid composition, proline and alanine were the most sensitive to heatwave treatment. Moreover, under the natural heatwave environment simulation validation experiment, the algae showed the same physiological performance as under laboratory conditions. The results indicated that marine heatwave events increased oxidative damage in S. fusiforme and inhibited carbon and nitrogen absorption and assimilation, ultimately leading to negative effects on the growth of algae. Thus, in the context of rapid global warming exacerbating marine heatwave events, our study provides valuable insights for high-temperature-resistant breeding and ecological management in coastal aquaculture.

Exploring the impact of ocean warming and nutrient overload on macroalgal blooms and carbon sequestration in deep-sea sediments of the subtropical western North Pacific

The role of macroalgae as blue carbon (BC) under changing climate was investigated in the subtropical western North Pacific. Sea surface temperatures (SSTs) and nutrient influx increased over the past two decades (2001-2021). The proliferation of climate-resilient macroalgae was facilitated. Using Pterocladiella capillacea and Turbinaria ornata, outdoor laboratory experiments and elemental assays underscored the influence of nutrient enrichment on their resilience under ocean warming and low salinity. Macroalgal incorporation into marine sediments, indicated by environmental DNA barcoding, total organic carbon (TOC), and stable isotope analysis. Over time, an increase in δ13C and δ15N values, particularly at greater depths, suggests a tendency of carbon signature towards macroalgaeand nitrogen pollution or high tropic levels. eDNA analysis revealed selective deposition of these species. The species-dependent nature of macroalgae in deep-sea sediments highlights the role of nutrients on climate-resilient macroalgal blooms as carbon sinks in the western North Pacific.

Ocean warming and Marine Heatwaves unequally impact juvenile introduced and native oysters with implications for their coexistence and future distribution

Climate change is causing ocean warming (OW) and increasing the frequency, intensity, and duration of extreme weather events, including Marine Heat Waves (MHWs). Both OW and MHWs pose a significant threat to marine ecosystems and marine organisms, including oysters, oyster reefs and farmed oysters. We investigated the survival and growth of juveniles of two commercial species of oyster, the Sydney rock oyster, Saccostrea glomerata, and the Pacific oyster, Crassostrea gigas, to elevated seawater temperatures reflecting a moderate and an extreme MHW in context with recent MHWs and beyond. The survival and size of Pacific oysters to moderate MHWs (22-32 °C; 14 days) was greater than that for Sydney rock oysters (24-32 °C; 15 days). While survival and growth of both species was significantly impacted by extreme MHWs (29-38 °C; 5-6 days), Sydney rock oysters were found to survive greater temperatures compared to the Pacific oyster. Overall, this study found that Pacific oyster juveniles were more tolerant of a moderate MHW, while Sydney rock oyster juveniles were more resilient to extreme MHWs. These differences in thermal tolerance may have consequences for aquaculture and coexistence of both species in their intertidal and latitudinal distributions along the south-eastern Australian coastline.

Gene expression response under thermal stress in two Hawaiian corals is dominated by ploidy and genotype

Transcriptome data are frequently used to investigate coral bleaching; however, the factors controlling gene expression in natural populations of these species are poorly understood. We studied two corals, Montipora capitata and Pocillopora acuta, that inhabit the sheltered Kāne'ohe Bay, Hawai'i. M. capitata colonies in the bay are outbreeding diploids, whereas P. acuta is a mixture of clonal diploids and triploids. Populations were sampled from six reefs and subjected to either control (no stress), thermal stress, pH stress, or combined pH and thermal stress treatments. RNA-seq data were generated to test two competing hypotheses: (1) gene expression is largely independent of genotype, reflecting a shared treatment-driven response (TDE) or, (2) genotype dominates gene expression, regardless of treatment (GDE). Our results strongly support the GDE model, even under severe stress. We suggest that post-transcriptional processes (e.g., control of translation, protein turnover) modify the signal from the transcriptome, and may underlie the observed differences in coral bleaching sensitivity via the downstream proteome and metabolome.

Earth at risk: An urgent call to end the age of destruction and forge a just and sustainable future

Human development has ushered in an era of converging crises: climate change, ecological destruction, disease, pollution, and socioeconomic inequality. This review synthesizes the breadth of these interwoven emergencies and underscores the urgent need for comprehensive, integrated action. Propelled by imperialism, extractive capitalism, and a surging population, we are speeding past Earth's material limits, destroying critical ecosystems, and triggering irreversible changes in biophysical systems that underpin the Holocene climatic stability which fostered human civilization. The consequences of these actions are disproportionately borne by vulnerable populations, further entrenching global inequities. Marine and terrestrial biomes face critical tipping points, while escalating challenges to food and water access foreshadow a bleak outlook for global security. Against this backdrop of Earth at risk, we call for a global response centered on urgent decarbonization, fostering reciprocity with nature, and implementing regenerative practices in natural resource management. We call for the elimination of detrimental subsidies, promotion of equitable human development, and transformative financial support for lower income nations. A critical paradigm shift must occur that replaces exploitative, wealth-oriented capitalism with an economic model that prioritizes sustainability, resilience, and justice. We advocate a global cultural shift that elevates kinship with nature and communal well-being, underpinned by the recognition of Earth's finite resources and the interconnectedness of its inhabitants. The imperative is clear: to navigate away from this precipice, we must collectively harness political will, economic resources, and societal values to steer toward a future where human progress does not come at the cost of ecological integrity and social equity.