Subcontinental heat wave triggers terrestrial and marine, multi-taxa responses

Co-occurrence of marine and atmospheric heatwaves with drought conditions and fire activity in the Mediterranean region

Climate change has become a major concern in the twenty-first century, leading to the amplification of extreme events and, consequently, to severe impacts on society, economy and ecosystems. Heatwave conditions in particular, often coupled with extended periods of dryness, have an important contribution in exacerbating rural fires. Here, we propose to analyse the co-occurring interplay between atmospheric heatwaves and droughts in southern Europe, and marine heatwaves in the East Atlantic and the Mediterranean Sea, between 2001 and 2022, highlighting their linkage to wildfires, on both an individual and compound approach. Positive correlations between air and sea temperatures and negative correlations between air temperature and precipitation values were found. Our analysis reveals that severe wildfires are mostly associated with reduced precipitation and/or elevated air temperatures during the summer season, alongside heightened sea surface temperatures. Marine hot (drier) conditions are prevalent for months in which burned areas remain below (above) the 80th percentile. Months marked by higher fire activity are predominantly associated with extreme climatic conditions, showcasing a substantial occurrence of compound events. This study highlights the potential of considering both land-based atmospheric and marine conditions when exploring compound extremes, crucial for mitigating climatic disasters. Moreover, it highlights the role played by compound extreme events in fire management strategies, particularly considering the present context of climate change and the increasing frequency and severity of extreme events threatening ecosystem stability.

Humidity modifies species-specific and age-dependent heat stress effects in an insect host-parasitoid interaction

Climate change is projected to increase the frequency and intensity of extreme heat events, and may increase humidity levels, leading to coupled thermal and hydric stress. However, how humidity modulates the impacts of heat stress on species and their interactions is currently unknown. Using an insect host-parasitoid interaction: the Indian meal moth, Plodia interpunctella, and its endoparasitoid wasp, Venturia canescens, we investigated how humidity interacted with heat stress duration, applied at different host developmental stages, to affect life history traits. Hosts parasitized as 4th instar larvae and unparasitized hosts were maintained in high- (60.8% RH) or low-humidity (32.5% RH) at constant 28°C. They were then exposed to a 38°C thermal stress with a duration of 0 (no heat stress), 6 or 72 h in either the 4th or 5th host instar. Neither humidity nor heat stress duration affected emergence of unparasitized hosts, but increasing heat stress duration during the 4th instar decreased parasitoid emergence irrespective of humidity. When applied during the 5th instar, increasing heat duration decreased parasitoid emergence under low humidity, but no effect of heat stress was found under high humidity. Moreover, experiencing longer heat stress in the 4th instar increased host larval development time and decreased body size under high humidity, but this effect differed under low humidity; increasing heat duration in the 5th instar decreased parasitoid body sizes only under low humidity. Larval stage and heat stress duration directly affected parasitized host survival time, with a concomitant indirect reduction of parasitoid sizes. We show that humidity modifies key life history responses of hosts and parasitoids to heat stress in species-specific ways, highlighting the potential importance of humidity in regulating host-parasitoid interactions and their population dynamics. Finally, we emphasize that interactions between environmental stressors need to be considered in climate change research.

Tree rings reveal the transient risk of extinction hidden inside climate envelope forecasts

Given the importance of climate in shaping species' geographic distributions, climate change poses an existential threat to biodiversity. Climate envelope modeling, the predominant approach used to quantify this threat, presumes that individuals in populations respond to climate variability and change according to species-level responses inferred from spatial occurrence data-such that individuals at the cool edge of a species' distribution should benefit from warming (the "leading edge"), whereas individuals at the warm edge should suffer (the "trailing edge"). Using 1,558 tree-ring time series of an aridland pine (Pinus edulis) collected at 977 locations across the species' distribution, we found that trees everywhere grow less in warmer-than-average and drier-than-average years. Ubiquitous negative temperature sensitivity indicates that individuals across the entire distribution should suffer with warming-the entire distribution is a trailing edge. Species-level responses to spatial climate variation are opposite in sign to individual-scale responses to time-varying climate for approximately half the species' distribution with respect to temperature and the majority of the species' distribution with respect to precipitation. These findings, added to evidence from the literature for scale-dependent climate responses in hundreds of species, suggest that correlative, equilibrium-based range forecasts may fail to accurately represent how individuals in populations will be impacted by changing climate. A scale-dependent view of the impact of climate change on biodiversity highlights the transient risk of extinction hidden inside climate envelope forecasts and the importance of evolution in rescuing species from extinction whenever local climate variability and change exceeds individual-scale climate tolerances.

Competition Increases Risk of Species Extinction during Extreme Warming

AbstractTemperature and interspecific competition are fundamental drivers of community structure in natural systems and can interact to affect many measures of species performance. However, surprisingly little is known about the extent to which competition affects extinction temperatures during extreme warming. This information is important for evaluating future threats to species from extreme high-temperature events and heat waves, which are rising in frequency and severity around the world. Using experimental freshwater communities of rotifers and ciliates, this study shows that interspecific competition can lower the threshold temperature at which local extinction occurs, reducing time to extinction during periods of sustained warming by as much as 2 weeks. Competitors may lower extinction temperatures by altering biochemical characteristics of the natural environment that affect temperature tolerance (e.g., levels of dissolved oxygen, nutrients, and metabolic wastes) or by accelerating population decline through traditional effects of resource depletion on life history parameters that affect population growth rates. The results suggest that changes in community structure in space and time could drive variability in upper thermal limits.

Record-breaking marine heatwave in northern Yellow Sea during summer 2018: Characteristics, drivers and ecological impact

Globally, marine heatwaves (MHWs) are becoming more common, more intense, and longer-lasting. They could have a large ecological and societal impact when compounded by low oxygen concentrations or high acidity. Here, using a high-resolution satellite product and reanalysis datasets, we investigated the characteristics of the MHW at northern Yellow Sea (NYS) during mid-summer 2018 and the driving mechanisms of large-scale atmospheric circulations. Results showed that the MHW in mid-summer 2018 (lasting from 26 July to 18 August 2018) had been the most intense since 1982, reaching an anomaly peak of 5.15 °C. For the 2018 MHW, the onset rate was 0.49 °C/day, indicating that the reaction window was relatively short and hard to take mitigation measures, while the decline rate was 0.19 °C/day, meaning the coping window was long and easy to push an already stressed system. The synergy of the two large-scale dynamic systems, i.e., the northward-shifted western north Pacific subtropical high (WNPSH) and the northeastward-expanded South Asia high (SAH), was likely responsible for establishment and maintenance of the hot-weather conditions. These high-pressure systems could result in stronger descending motion, less cloud cover, more solar radiation, and smaller wind speeds which in combination aggravated the MHW. We further found that the unprecedented MHW was actually also impacted by terrestrial heatwave. From 14 July to 15 August 2018, Northeast China was affected by an exceptionally long and intense atmospheric heat wave (AHW). The AHW had impacted on the MHW through warm advection transportation and may significantly contribute to the record-breaking intensity of the MHW, in addition to the impact of abnormal atmospheric circulations. Finally, we showed that a mass mortality of sea cucumbers in the study region during mid-summer 2018 was highly likely caused by the MHW through severe heat stress.

Effects of heatwave events on the seagrass-dwelling crustacean Pandalus latirostris in a subarctic lagoon

Heatwaves often cause mass mortality of organisms in seagrass areas, and they eventually alter some ecological functions of seagrass ecosystems. In subarctic regions, however, the effects of heatwaves on seagrass areas are still unclear. In a subarctic lagoon of northern Japan, we examined the effects of heatwaves on the Hokkai shrimp, Pandalus latirostris, a commercially exploited species distributed in seagrass areas of northern Japan and eastern Russia. A long-term survey of the surface water temperature in the lagoon clarified a gradual increase in the frequency and intensity of heatwave events since 1999. Surveys of the water temperature at a seagrass area in the lagoon during summer have also demonstrated that the maximum water temperature had been exceeding 25 °C, unusually high for this location, regardless of water depth. These results indicate that the effects of heatwaves in seagrass areas in a subarctic region had become as severe as those in tropical and temperate regions. We also experimentally evaluated the effects of this unusually high water temperature (25 °C) on the survival of P. latirostris by changing the length of exposure time. Some individuals suffered damage to their intestinal mucosal structure after exposure for 12 h or longer, and all individuals died after exposure for 120 h. Our results suggest that heatwaves possibly cause mass mortality in P. latirostris in the following sequence: heat stress, damage to the intestinal epithelial mucosal structure, degradation of nutrient absorption and immunological function of the intestine, energy deficiency and disease infection, and finally mortality. This study, conducted in subarctic closed waters, concludes that it is essential to become familiar with not only trends in heatwaves but also the intermittent occurrence of unusually high water temperature in seagrass areas in order to better understand the process of mortality of organisms that inhabit these ecosystems.

Demographic consequences of an extreme heat wave are mitigated by spatial heterogeneity in an annual monkeyflower

Heat waves are becoming more frequent and intense with climate change, but the demographic and evolutionary consequences of heat waves are rarely investigated in herbaceous plant species. We examine the consequences of a short but extreme heat wave in Oregon populations of the common yellow monkeyflower (Mimulus guttatus) by leveraging a common garden experiment planted with range-wide populations and observational studies of 11 local populations. In the common garden, 89% of seedlings died during the heat wave including >96% of seedlings from geographically local populations. Some populations from hotter and drier environments had higher fitness, however, others from comparable environments performed poorly. Observational studies of local natural populations drastically differed in the consequences of the heat wave-one population was completely extirpated and nearly half had a >50% decrease in fitness. However, a few populations had greater fitness during the heat wave year. Differences in mortality corresponded to the impact of the heat wave on soil moisture-retention of soil moisture throughout the heat wave led to greater survivorship. Our results suggest that not all populations experience the same intensity or degree of mortality during extreme events and such heterogeneity could be important for genetic rescue or to facilitate the distribution of adaptive variants throughout the region.

More frequent, persistent, and deadly heat waves in the 21st century over the Eastern Mediterranean

Heat waves are extreme events characterized by sweltering weather over an extended period. Skillful projections of heat waves and their impacts on human mortality can help develop appropriate adaptation strategies. Here, we provide nuanced projections of heat wave characteristics and their effect on human mortality over the Eastern Mediterranean based on ERA5 reanalysis and CORDEX ensemble simulations. Heat waves were identified according to the 90th percentile threshold of the Climatic Stress Index (CSI), specifically tailored for the summer conditions in this region. We provide evidence that heat waves in the region are projected to occur seven times more often and last three times longer by the end of the 21st century (RCP8.5). We find that heat waves will become more persistent in a warmer world. Finally, we offer a conservative estimate of excess mortality in Israel based on a simple linear model. The projected changes in heat stress intensity and frequency may result in ~330 excess deaths per summer at the end of the 21st century (RCP8.5) compared to the historical baseline of ~30 heat-related deaths, particularly pronounced in the elderly (65+ years). We conclude that heat waves increasingly threaten society in the vulnerable Eastern Mediterranean. We also emphasize that true interdisciplinary regional collaborations are required to achieve adequate public health adaptation to extreme weather events in a changing climate.

Interactions between dissolved organic matter and the microbial community are modified by microplastics and heat waves

Dissolved organic matter (DOM) exists widely in natural waters and plays an important role in river carbon cycles and greenhouse gas emissions through microbial interactions. However, information on DOM-microbe associations in response to environmental stress is limited. River environments are the main carriers of microplastic (MP) pollution, and global heat waves (HWs) are threatening river ecology. Here, through MP exposure and HW simulation experiments, we found that DOM molecular weight and aromaticity were closely related to initial microbial communities. Moreover, MP-derived DOM regulated microbial community abundance and diversity, influenced microorganism succession trajectories as deterministic factors, and competed with riverine DOM for microbial utilization. SimulatedHWs enhanced the MP-derived DOM competitive advantage and drove the microbial community to adopt a K-strategy for effective recalcitrant carbon utilization. Relative to single environmental stressor exposure, combined MP pollution and HWs led to a more unstable microbial network. This study addresses how MPs and HWs drive DOM-microbe interactions in rivers, contributes to an in-depth understanding of the fate of river DOM and microbial community succession processes, and narrows the knowledge gap in understanding carbon sinks in aquatic ecosystems influenced by human activities and climate change.

Drought then wildfire reveals a compound disturbance in a resprouting forest

The frequency and intensity of forest disturbances, such as drought and fire, are increasing globally, with an increased likelihood of multiple disturbance events occurring in short succession. Disturbances layered over one another may influence the likelihood or intensity of subsequent events (a linked disturbance) or impact response and recovery trajectories (a compound disturbance), with substantial implications for ecological spatiotemporal vulnerability. This study evaluates evidence for disturbance interactions of drought followed by wildfire in a resprouting eucalypt-dominated forest (the Northern Jarrah Forest) in southwestern Australia. Sites were stratified by drought (high, low), from previous modeling and ground validation, and fire severity (high, moderate, unburnt), via remote sensing using the relative difference normalized burn ratio (RdNBR). Evidence of a linked disturbance was assessed via fine fuel consumption and fire severity. Compound disturbance effects were quantified at stand scale (canopy height, quadratic mean diameter, stem density) and stem scale (mortality). There was no evidence of prior drought influencing fine fuel consumption or fire severity and, hence, no evidence of a linked disturbance. However, compound disturbance effects were evident; stands previously affected by drought experienced smaller shifts in canopy height, quadratic mean diameter, and stem density than stands without prior drought impact. At the stem scale, size and fire severity were the strongest determinants of stem survival. Proportional resprouting height was greater in high drought sites than in low drought sites (p < 0.01), meaning, structurally, the low drought stands decreased in height more than the high drought stands. Thus, a legacy of the drought was evident after the wildfire. Although these resprouting eucalypt forests have been regarded as particularly resilient, this study illustrates how multiple disturbances can overwhelm the larger tree component and promote an abundance of smaller stems. We suggest that this is early evidence of a structural destabilization of these forests under a more fire-prone, hotter, and drier future climate.

Climate change mitigation by coral reefs and seagrass beds at risk: How global change compromises coastal ecosystem services

Seagrass meadows provide valuable ecosystem services of coastal protection and chemical habitat formation that could help mitigate the impact of sea level rise and ocean acidification. However, the intensification of hydrodynamic forces caused by sea level rise, in addition to habitat degradation threaten the provision of these ecosystem services. With quantitative field measurements of the coastal protection and chemical habitat formation services of seagrass meadows, we statistically model the relationships between hydrodynamic forces, vegetation density and the provision of these ecosystem services. Utilising a high-resolution hydrodynamic model that simulates end of the century hydrodynamic conditions and three scenarios of coral reef degradation (i.e., keep up, remain or loss) we quantify how the environmental conditions within a tropical bay will change given changes to the provision of ecosystem services. Our study shows that increasing hydrodynamic forces lead to a seafloor made up of a larger grain size that is increasingly unstable and more vulnerable to erosion. The loss of a fringing reef leads to larger hydrodynamic forces entering the bay, however, the 0.87 m increase in depth due to sea-level rise reduces the bed shear stress in shallower areas, which limits the change in the ecosystem services provided by the current benthic seagrass meadow. Loss of seagrass constitutes the greatest change in a bay ecosystem, resulting in the sediment surface where seagrass existed becoming unstable and the median sediment grain size increasing by 5-7 %. The loss of seagrass also leads to the disappearance of the unique fluctuating chemical habitat, which leaves the surrounding community vulnerable to ocean acidification. A reduction or complete loss of these ecosystem services would impact the entire community assemblage while also leaving the surrounding coastline vulnerable to erosion, thus exacerbating negative effects brought about by climate change.

Extensive polyploid clonality was a successful strategy for seagrass to expand into a newly submerged environment

Polyploidy has the potential to allow organisms to outcompete their diploid progenitor(s) and occupy new environments. Shark Bay, Western Australia, is a World Heritage Area dominated by temperate seagrass meadows including Poseidon's ribbon weed, Posidonia australis. This seagrass is at the northern extent of its natural geographic range and experiences extremes in temperature and salinity. Our genomic and cytogenetic assessments of 10 meadows identified geographically restricted, diploid clones (2n = 20) in a single location, and a single widespread, high-heterozygosity, polyploid clone (2n = 40) in all other locations. The polyploid clone spanned at least 180 km, making it the largest known example of a clone in any environment on earth. Whole-genome duplication through polyploidy, combined with clonality, may have provided the mechanism for P. australis to expand into new habitats and adapt to new environments that became increasingly stressful for its diploid progenitor(s). The new polyploid clone probably formed in shallow waters after the inundation of Shark Bay less than 8500 years ago and subsequently expanded via vegetative growth into newly submerged habitats.

Climate Change Risks to Global Forest Health: Emergence of Unexpected Events of Elevated Tree Mortality Worldwide

Recent observations of elevated tree mortality following climate extremes, like heat and drought, raise concerns about climate change risks to global forest health. We currently lack both sufficient data and understanding to identify whether these observations represent a global trend toward increasing tree mortality. Here, we document events of sudden and unexpected elevated tree mortality following heat and drought events in ecosystems that previously were considered tolerant or not at risk of exposure. These events underscore the fact that climate change may affect forests with unexpected force in the future. We use the events as examples to highlight current difficulties and challenges for realistically predicting such tree mortality events and the uncertainties about future forest condition. Advances in remote sensing technology and greater availably of high-resolution data, from both field assessments and satellites, are needed to improve both understanding and prediction of forest responses to future climate change.

Global field observations of tree die-off reveal hotter-drought fingerprint for Earth's forests

Earth's forests face grave challenges in the Anthropocene, including hotter droughts increasingly associated with widespread forest die-off events. But despite the vital importance of forests to global ecosystem services, their fates in a warming world remain highly uncertain. Lacking is quantitative determination of commonality in climate anomalies associated with pulses of tree mortality-from published, field-documented mortality events-required for understanding the role of extreme climate events in overall global tree die-off patterns. Here we established a geo-referenced global database documenting climate-induced mortality events spanning all tree-supporting biomes and continents, from 154 peer-reviewed studies since 1970. Our analysis quantifies a global "hotter-drought fingerprint" from these tree-mortality sites-effectively a hotter and drier climate signal for tree mortality-across 675 locations encompassing 1,303 plots. Frequency of these observed mortality-year climate conditions strongly increases nonlinearly under projected warming. Our database also provides initial footing for further community-developed, quantitative, ground-based monitoring of global tree mortality.

In the Hot Seat: Behavioral Change and Old-Growth Trees Underpin an Australian Songbird’s Response to Extreme Heat

Anthropogenic climate change is increasing the frequency and intensity of heat waves, thereby threatening biodiversity, particularly in hot, arid regions. Although free-ranging endotherms can use behavioral thermoregulation to contend with heat, it remains unclear to what degree behavior can buffer organisms from unprecedented temperatures. Thermoregulatory behaviors that facilitate dry heat loss during moderate heat become maladaptive once environmental temperatures exceed body temperature. Additionally, the costs associated with behavioral thermoregulation may become untenable with greater heat exposure, and effective cooling may be dependent upon the availability of specific microhabitats. Only by understanding the interplay of these three elements (responses, costs and habitat) can we hope to accurately predict how heat waves will impact wild endotherms. We quantified the thermoregulatory behaviors and microhabitat use of a small passerine, the Jacky Winter (Microeca fascinans), in the mallee woodland of SE Australia. At this location, the annual number of days ≥ 42°C has doubled over the last 25 years. The birds’ broad repertoire of behavioral responses to heat was nuanced and responsive to environmental conditions, but was associated with reduced foraging effort and increased foraging costs, accounting for the loss of body condition that occurs at high temperatures. By measuring microsite surface temperatures, which varied by up to 35°C at air temperatures &gt; 44°C, we found that leaf-litter coverage and tree size were positively correlated with thermal buffering. Large mallee eucalypts were critical to the birds’ response to very high temperatures, providing high perches that facilitated convective cooling, the coolest tree-base temperatures and the greatest prevalence of tree-base crevices or hollows that were used as refuges at air temperatures &gt; 38°C. Tree-base hollows, found only in large mallees, were cooler than all other microsites, averaging 2°C cooler than air temperature. Despite the plasticity of the birds’ response to heat, 29% of our habituated study population died when air temperatures reached a record-breaking 49°C, demonstrating the limits of behavioral thermoregulation and the potential vulnerability of organisms to climate change.

Extreme heat increases stomatal conductance and drought-induced mortality risk in vulnerable plant species

Tree mortality during global-change-type drought is usually attributed to xylem dysfunction, but as climate change increases the frequency of extreme heat events, it is necessary to better understand the interactive role of heat stress. We hypothesized that some drought-stressed plants paradoxically open stomata in heatwaves to prevent leaves from critically overheating. We experimentally imposed heat (>40°C) and drought stress onto 20 broadleaf evergreen tree/shrub species in a glasshouse study. Most well-watered plants avoided lethal overheating, but drought exacerbated thermal damage during heatwaves. Thermal safety margins (TSM) quantifying the difference between leaf surface temperature and leaf critical temperature, where photosynthesis is disrupted, identified species vulnerability to heatwaves. Several mechanisms contributed to high heat tolerance and avoidance of damaging leaf temperatures-small leaf size, low leaf osmotic potential, high leaf mass per area (i.e., thick, dense leaves), high transpirational capacity, and access to water. Water-stressed plants had smaller TSM, greater crown dieback, and a fundamentally different stomatal heatwave response relative to well-watered plants. On average, well-watered plants closed stomata and decreased stomatal conductance (g_s ) during the heatwave, but droughted plants did not. Plant species with low g_s , either due to isohydric stomatal behavior under water deficit or inherently low transpirational capacity, opened stomata and increased g_s under high temperatures. The current paradigm maintains that stomata close before hydraulic thresholds are surpassed, but our results suggest that isohydric species may dramatically increase g_s (over sixfold increases) even past their leaf turgor loss point. By actively increasing water loss at high temperatures, plants can be driven toward mortality thresholds more rapidly than has been previously recognized. The inclusion of TSM and responses to heat stress could improve our ability to predict the vulnerability of different tree species to future droughts.

Estimating the Evaporative Cooling Effect of Irrigation within and above Soybean Canopy

Vegetation with an adequate supply of water might contribute to cooling the land surface around it through the latent heat flux of transpiration. This study investigates the potential estimation of evaporative cooling at plot scale, using soybean as example. Some of the plants’ physiological parameters were monitored and sampled at weekly intervals. A physics-based model was then applied to estimate the irrigation-induced cooling effect within and above the canopy during the middle and late season of the soybean growth period. We then examined the results of the temperature changes at a temporal resolution of ten minutes between every two irrigation rounds. During the middle and late season of growth, the cooling effects caused by evapotranspiration within and above the canopy were, on average, 4.4 K and 2.9 K, respectively. We used quality indicators such as R-squared (R2) and mean absolute error (MAE) to evaluate the performance of the model simulation. The performance of the model in this study was better above the canopy (R2 = 0.98, MAE = 0.3 K) than below (R2 = 0.87, MAE = 0.9 K) due to the predefined thermodynamic condition used to estimate evaporative cooling. Moreover, the study revealed that canopy cooling contributes to mitigating heat stress conditions during the middle and late seasons of crop growth.

Repeated extreme heatwaves result in higher leaf thermal tolerances and greater safety margins

The frequency and severity of heatwave events are increasing, exposing species to conditions beyond their physiological limits. Species respond to heatwaves in different ways, however it remains unclear if plants have the adaptive capacity to successfully respond to hotter and more frequent heatwaves. We exposed eight tree populations from two climate regions grown under cool and warm temperatures to repeated heatwave events of moderate (40°C) and extreme (46°C) severity to assess adaptive capacity to heatwaves. Leaf damage and maximum quantum efficiency of photosystem II (F_v /F_m ) were significantly impacted by heatwave severity and growth temperatures, respectively; populations from a warm-origin avoided damage under moderate heatwaves compared to those from a cool-origin, indicating a degree of local adaptation. We found that plasticity to heatwave severity and repeated heatwaves contributed to enhanced thermal tolerance and lower leaf temperatures_, leading to greater thermal safety margins (thermal tolerance minus leaf temperature) in a second heatwave. Notably, while we show that adaptation and physiological plasticity are important factors affecting plant adaptive capacity to thermal stress, plasticity of thermal tolerances and thermal safety margins provides the opportunity for trees to persist among fluctuating heatwave exposures.

Phytoplankton mortality in a changing thermal seascape

Predicting spatiotemporal distributions of phytoplankton biomass and community composition heavily relies on experimental studies that document how environmental conditions influence population growth rates. In unicellular phytoplankton, the net population growth rate is the difference between the cell division rate and the death rate. Along with predation and disease, phytoplankton mortality arises from abiotic stress. Although the effect of temperature on the net population growth rate is well understood, studies examining thermally induced death rates in phytoplankton are scarce. We investigated how cell division and death rates of the diatom Phaeodactylum tricornutum varied within its thermal tolerance limits (thermal niche), and at temperatures just above its upper thermal tolerance limit. We show that death rates were largely independent of temperature when P. tricornutum was grown within its thermal niche, but increased significantly at temperatures that approached or exceeded its upper thermal tolerance limit. Furthermore, the sensitivity of mortality increased with the duration of exposure to heat stress and was affected by the pre-acclimation temperature. Heat waves can be expected to significantly affect phytoplankton mortality episodically. The increasing frequency of heat waves accompanying global warming can be expected to drive changes in phytoplankton community structure due to interspecific variability of thermal niches with potential implications for food web dynamics and biogeochemical cycles.

Late-stage pregnancy reduces upper thermal tolerance in a live-bearing fish

Upper thermal limits are considered a key determinant of a population's ability to persist in the face of extreme heat events. However, these limits differ considerably among individuals within a population, and the mechanisms underlying this differential sensitivity are not well understood. Upper thermal tolerance in aquatic ectotherms is thought to be determined by a mismatch between oxygen supply and the increased metabolic demands associated with warmer waters. As such, tolerance is expected to decline during reproduction given the heightened oxygen demand for gamete production and maintenance. Among live-bearing species, upper thermal tolerance of reproductive adults may decline even further after fertilization due to the cost of meeting the increasing oxygen demands of developing embryos. We examined the upper thermal tolerance of live-bearing female Trinidadian guppies at different stages of reproduction and found that critical thermal maximum was similar during the egg yolking and early embryos stage but then declined by almost 0.5 °C during late pregnancy when oxygen demands are the greatest. These results are consistent with the hypothesis that oxygen limitation sets thermal limits and show that reproduction is associated with a decline in upper thermal tolerance.

Underappreciated plant vulnerabilities to heat waves

With climate change, heat waves are becoming increasingly frequent, intense and broader in spatial extent. However, while the lethal effects of heat waves on humans are well documented, the impacts on flora are less well understood, perhaps except for crops. We summarize recent findings related to heat wave impacts including: sublethal and lethal effects at leaf and plant scales, secondary ecosystem effects, and more complex impacts such as increased heat wave frequency across all seasons, and interactions with other disturbances. We propose generalizable practical trials to quantify the critical bounding conditions of vulnerability to heat waves. Collectively, plant vulnerabilities to heat waves appear to be underappreciated and understudied, particularly with respect to understanding heat wave driven plant die-off and ecosystem tipping points.

Birds of different morphs use slightly different strategies to achieve similar reproductive performance following heatwave exposure

Responses to extreme climatic events may differ between individuals of distinct morphs which differ in life-history strategies, resulting in climate change 'winners' and 'losers' within species. We examined the reproductive performance and carry-over effects on offspring of black- and red-headed Gouldian finches Erythrura gouldiae after exposure to simulated heatwaves of moderate or severe intensity. We expected black-headed pairs' reproductive performance to decline after the severe heatwave because only the condition of black-headed females deteriorates during such a heatwave. Supporting the fact that Gouldian finches of different morphs use alternative reproductive strategies, we found that black-headed females initiated egg-laying a month earlier than red-headed females after experiencing a severe heatwave. We also found that this severe heatwave resulted in shorter spermatozoa in males irrespective of their morph. Despite these effects associated with heatwave intensity, the overall reproductive performance of both morphs was not affected by this factor, which was possibly due to an increased nestling provisioning rate by parents after exposure to the severe heatwave. However, offspring still bore the cost of parental exposure to the severe heatwave, as they showed a reduced condition (lower plasma antioxidant capacity and transient lower breathing rate) and higher oxidative damage (at least in fledglings with black-headed parents). These results suggest that inter-morph phenotypic variability in the Gouldian finch does not result in clear differences in reproductive performance following heatwave exposure, despite basal phenotypic differences between morphs. Whether animals using alternative reproductive strategies are, in the end, differently affected by climate changes will likely depend on the capacity of their offspring to recover from altered developmental conditions.

Global meta-analysis of tree decline impacts on fauna

Significant portions of the world's forests have been impacted by severe and large-scale tree declines characterised by gradual but widespread loss of vigour and subsequent death of either single or several tree species. Tree deaths represent a threat for fauna that are dependent on forest habitats for their survival. Although tree declines have received considerable scientific attention, surprisingly, little is known about their impacts on fauna. In total, we calculated 631 effect sizes across 59 studies that quantified the impact of tree declines on animal abundance. Data representing 186 bird species indicated an overall increase in bird abundance in response to tree declines (meta-analysis mean ± estimation g = 0.172 ± 0.053 [CI 0.069 to 0.275], P = 0.001); however, there was substantial variability in responses (significant heterogeneity P < 0.001) with a strong influence of diet as well as nesting guild on bird responses. Granivores (especially ground-foraging species, e.g. Passerellidae species), bark-foraging insectivores (e.g. woodpeckers), as well as ground- and cavity-nesting species apparently benefitted from tree declines, while nectarivorous birds [and, although not significant, aerially foraging insectivores (e.g. flycatchers) and leaf-gleaning insectivores (canopy-feeding)] were less common in the presence of tree declines. Data representing 33 mammal species indicate a tendency for detrimental effects of tree declines on mammals that use trees as refuges, while aerial foragers (i.e. bats) may benefit from opening up the canopy. Overall the average effect for mammals was neutral (meta-analysis mean estimation g = -0.150 ± 0.145 [-0.433 to 0.134], P = 0.302). Data representing 20 reptile species showed an insufficient range of responses to determine any diet or foraging effect on their responses. Data for 28 arthropod taxa should be considered with caution, as we could not adequately separate taxa according to their specialisations and reliance on key habitat. The data broadly suggest a detrimental effect of tree declines (meta-analysis mean estimation g = -0.171 ± 0.072 [-0.311 to -0.031], P = 0.017) with ground-foraging arthropods (e.g. detritivores and predators such as spiders and centipedes) more likely to be detrimentally impacted by tree declines. The range of responses to tree declines signifies substantially altered animal communities. In many instances, altered ecosystem function due to loss of key animal services will represent a significant threat to forest health.

Heatwave-induced synchrony within forage fish portfolio disrupts energy flow to top pelagic predators

During the Pacific marine heatwave of 2014-2016, abundance and quality of several key forage fish species in the Gulf of Alaska were simultaneously reduced throughout the system. Capelin (Mallotus catervarius), sand lance (Ammodytes personatus), and herring (Clupea pallasii) populations were at historically low levels, and within this community abrupt declines in portfolio effects identify trophic instability at the onset of the heatwave. Although compensatory changes in age structure, size, growth or energy content of forage fish were observed to varying degrees among all these forage fish, none were able to fully mitigate adverse impacts of the heatwave, which likely included both top-down and bottom-up forcing. Notably, changes to the demographic structure of forage fish suggested size-selective removals typical of top-down regulation. At the same time, changes in zooplankton communities may have driven bottom-up regulation as copepod community structure shifted toward smaller, warm water species, and euphausiid biomass was reduced owing to the loss of cold-water species. Mediated by these impacts on the forage fish community, an unprecedented disruption of the normal pelagic food web was signaled by higher trophic level disruptions during 2015-2016, when seabirds, marine mammals, and groundfish experienced shifts in distribution, mass mortalities, and reproductive failures. Unlike decadal-scale variability underlying ecosystem regime shifts, the heatwave appeared to temporarily overwhelm the ability of the forage fish community to buffer against changes imposed by warm water anomalies, thereby eliminating any ecological advantages that may have accrued from having a suite of coexisting forage species with differing life-history compensations.

Combating ecosystem collapse from the tropics to the Antarctic

Globally, collapse of ecosystems-potentially irreversible change to ecosystem structure, composition and function-imperils biodiversity, human health and well-being. We examine the current state and recent trajectories of 19 ecosystems, spanning 58° of latitude across 7.7 M km² , from Australia's coral reefs to terrestrial Antarctica. Pressures from global climate change and regional human impacts, occurring as chronic 'presses' and/or acute 'pulses', drive ecosystem collapse. Ecosystem responses to 5-17 pressures were categorised as four collapse profiles-abrupt, smooth, stepped and fluctuating. The manifestation of widespread ecosystem collapse is a stark warning of the necessity to take action. We present a three-step assessment and management framework (3As Pathway Awareness, Anticipation and Action) to aid strategic and effective mitigation to alleviate further degradation to help secure our future.

Marine Heatwaves

Ocean temperature variability is a fundamental component of the Earth's climate system, and extremes in this variability affect the health of marine ecosystems around the world. The study of marine heatwaves has emerged as a rapidly growing field of research, given notable extreme warm-water events that have occurred against a background trend of global ocean warming. This review summarizes the latest physical and statistical understanding of marine heatwaves based on how they are identified, defined, characterized, and monitored through remotely sensed and in situ data sets. We describe the physical mechanisms that cause marine heatwaves, along with their global distribution, variability, and trends. Finally, we discuss current issues in this developing research area, including considerations related to thechoice of climatological baseline periods in defining extremes and how to communicate findings in the context of societal needs.

Seascape Genomics of the Sugar Kelp Saccharina latissima along the North Eastern Atlantic Latitudinal Gradient

Temperature is one of the most important range-limiting factors for many seaweeds. Driven by the recent climatic changes, rapid northward shifts of species' distribution ranges can potentially modify the phylogeographic signature of Last Glacial Maximum. We explored this question in detail in the cold-tolerant kelp species Saccharina latissima, using microsatellites and double digest restriction site-associated DNA sequencing ( ddRAD-seq) derived single nucleotide polymorphisms (SNPs) to analyze the genetic diversity and structure in 11 sites spanning the entire European Atlantic latitudinal range of this species. In addition, we checked for statistical correlation between genetic marker allele frequencies and three environmental proxies (sea surface temperature, salinity, and water turbidity). Our findings revealed that genetic diversity was significantly higher for the northernmost locality (Spitsbergen) compared to the southern ones (Northern Iberia), which we discuss in light of the current state of knowledge on phylogeography of S. latissima and the potential influence of the recent climatic changes on the population structure of this species. Seven SNPs and 12 microsatellite alleles were found to be significantly associated with at least one of the three environmental variables. We speculate on the putative adaptive functions of the genes associated with the outlier markers and the importance of these markers for successful conservation and aquaculture strategies for S. latissima in this age of rapid global change.

Heat wave effects on the behavior and life-history traits of sedentary antlions

Research on the behavioral responses of animals to extreme weather events, such as heat wave, is lacking even though their frequency and intensity in nature are increasing. Here, we investigated the behavioral response to a simulated heat wave in two species of antlions (Neuroptera: Myrmeleontidae). These insects spend the majority of their lives as larvae and live in sandy areas suitable for a trap-building hunting strategy. We used larvae of Myrmeleon bore and Euroleon nostras, which are characterized by different microhabitat preferences-sunlit in the case of M. bore and shaded in the case of E. nostras. Larvae were exposed to fluctuating temperatures (40 °C for 10 h daily and 25 °C for the remaining time) or a constant temperature (25 °C) for an entire week. We found increased mortality of larvae under heat. We detected a reduction in the hunting activity of larvae under heat, which corresponded to changes in the body mass of individuals. Furthermore, we found long-term consequences of the simulated heat wave, as it prolonged the time larvae needed to molt. These effects were pronounced in the case of E. nostras but did not occur or were less pronounced in the case of M. bore, suggesting that microhabitat-specific selective pressures dictate how well antlions handle heat waves. We, thus, present results demonstrating the connection between behavior and the subsequent changes to fitness-relevant traits in the context of a simulated heat wave. These results illustrate how even closely related species may react differently to the same event.

Heat stress responses and population genetics of the kelp Laminaria digitata (Phaeophyceae) across latitudes reveal differentiation among North Atlantic populations

To understand the thermal plasticity of a coastal foundation species across its latitudinal distribution, we assess physiological responses to high temperature stress in the kelp Laminaria digitata in combination with population genetic characteristics and relate heat resilience to genetic features and phylogeography. We hypothesize that populations from Arctic and cold-temperate locations are less heat resilient than populations from warm distributional edges. Using meristems of natural L. digitata populations from six locations ranging between Kongsfjorden, Spitsbergen (79°N), and Quiberon, France (47°N), we performed a common-garden heat stress experiment applying 15°C to 23°C over eight days. We assessed growth, photosynthetic quantum yield, carbon and nitrogen storage, and xanthophyll pigment contents as response traits. Population connectivity and genetic diversity were analyzed with microsatellite markers. Results from the heat stress experiment suggest that the upper temperature limit of L. digitata is nearly identical across its distribution range, but subtle differences in growth and stress responses were revealed for three populations from the species' ecological range margins. Two populations at the species' warm distribution limit showed higher temperature tolerance compared to other populations in growth at 19°C and recovery from 21°C (Quiberon, France), and photosynthetic quantum yield and xanthophyll pigment responses at 23°C (Helgoland, Germany). In L. digitata from the northernmost population (Spitsbergen, Norway), quantum yield indicated the highest heat sensitivity. Microsatellite genotyping revealed all sampled populations to be genetically distinct, with a strong hierarchical structure between southern and northern clades. Genetic diversity was lowest in the isolated population of the North Sea island of Helgoland and highest in Roscoff in the English Channel. All together, these results support the hypothesis of moderate local differentiation across L. digitata's European distribution, whereas effects are likely too weak to ameliorate the species' capacity to withstand ocean warming and marine heatwaves at the southern range edge.

Heatwaves alter survival of the Sydney rock oyster, Saccostrea glomerata

Heatwaves are an increasing threat to organisms across the globe. Marine and atmospheric heatwaves are predicted to impact sessile intertidal marine organisms, especially when exposed at low tide and unable to seek refuge. The study aimed to determine whether a simulated atmospheric heatwave will alter the survival of selectively bred families of Sydney rock oysters (Saccostrea glomerata), and whether survival is dependent on morphological and physiological traits. The survival of S. glomerata families to a simulated atmospheric heatwave varied from 25 to 60% and was not correlated with morphology or physiology. Survival may depend on the presence of genotypes that translate into molecular defenses such as heat-shock proteins and inhibitor of apoptosis proteins that provide oysters with resilience. Understanding the responses among families of oysters to heatwaves is critical if we are to restore the ecological services of oyster reefs and sustain oyster aquaculture.

Physiological responses of wild zebra finches (Taeniopygia guttata) to heatwaves

Desert birds inhabit hot, dry environments that are becoming hotter and drier as a consequence of climate change. Extreme weather such as heatwaves can cause mass-mortality events that may significantly impact populations and species. There are currently insufficient data concerning physiological plasticity to inform models of species' response to extreme events and develop mitigation strategies. Consequently, we examine here the physiological plasticity of a small desert bird in response to hot (mean maximum ambient temperature=42.7°C) and cooler (mean maximum ambient temperature=31.4°C) periods during a single Austral summer. We measured body mass, metabolic rate, evaporative water loss and body temperature, along with blood parameters (corticosterone, glucose and uric acid) of wild zebra finches (Taeniopygia guttata) to assess their physiological state and determine the mechanisms by which they respond to heatwaves. Hot days were not significant stressors; they did not result in modification of baseline blood parameters or an inability to maintain body mass, provided drinking water was available. During heatwaves, finches shifted their thermoneutral zone to higher temperatures. They reduced metabolic heat production, evaporative water loss and wet thermal conductance, and increased hyperthermia, especially when exposed to high ambient temperature. A consideration of the significant physiological plasticity that we have demonstrated to achieve more favourable heat and water balance is essential for effectively modelling and planning for the impacts of climate change on biodiversity.

Too hot to handle: Unprecedented seagrass death driven by marine heatwave in a World Heritage Area

The increased occurrence of extreme climate events, such as marine heatwaves (MHWs), has resulted in substantial ecological impacts worldwide. To date, metrics of thermal stress within marine systems have focussed on coral communities, and less is known about measuring stress relevant to other primary producers, such as seagrasses. An extreme MHW occurred across the Western Australian coastline in the austral summer of 2010-2011, exposing marine communities to summer seawater temperatures 2-5°C warmer than average. Using a combination of satellite imagery and in situ assessments, we provide detailed maps of seagrass coverage across the entire Shark Bay World Heritage Area (ca. 13,000 km² ) before (2002 and 2010) and after the MHW (2014 and 2016). Our temporal analysis of these maps documents the single largest loss in dense seagrass extent globally (1,310 km² ) following an acute disturbance. Total change in seagrass extent was spatially heterogeneous, with the most extensive declines occurring in the Western Gulf, Wooramel Bank and Faure Sill. Spatial variation in seagrass loss was best explained by a model that included an interaction between two heat stress metrics, the most substantial loss occurring when degree heating weeks (DHWm) was ≥10 and the number of days exposed to extreme sea surface temperature during the MHW (DaysOver) was ≥94. Ground truthing at 622 points indicated that change in seagrass cover was predominantly due to loss of Amphibolis antarctica rather than Posidonia australis, the other prominent seagrass at Shark Bay. As seawater temperatures continue to rise and the incidence of MHWs increase globally, this work will provide a basis for identifying areas of meadow degradation, or stability and recovery, and potential areas of resilience.

Drought can offset potential water use efficiency of forest ecosystems from rising atmospheric CO2

Increasing atmospheric CO₂ is both leading to climate change and providing a potential fertilisation effect on plant growth. However, southern Australia has also experienced a significant decline in rainfall over the last 30 years, resulting in increased vegetative water stress. To better understand the dynamics and responses of Australian forest ecosystems to drought and elevated CO₂, the magnitude and trend in water use efficiency (WUE) of forests, and their response to drought and elevated CO₂ from 1982 to 2014 were analysed, using the best available model estimates constrained by observed fluxes from simulations with fixed and time-varying CO₂. The ratio of gross primary productivity (GPP) to evapotranspiration (ET) (WUEe) was used to identify the ecosystem scale WUE, while the ratio of GPP to transpiration (Tr) (WUEc) was used as a measure of canopy scale WUE. WUE increased significantly in northern Australia (p < 0.001) for woody savannas (WSA), whereas there was a slight decline in the WUE of evergreen broadleaf forests (EBF) in the southeast and southwest of Australia. The lag of WUEc to drought was consistent and relatively short and stable between biomes (≤3 months), but notably varied for WUEe, with a long time-lag (mean of 10 months). The dissimilar responses of WUEe and WUEc to climate change for different geographical areas result from the different proportion of Tr in ET. CO₂ fertilization and a wetter climate enhanced WUE in northern Australia, whereas drought offset the CO₂ fertilization effect in southern Australia.

Climatic and local stressor interactions threaten tropical forests and coral reefs

Tropical forests and coral reefs host a disproportionately large share of global biodiversity and provide ecosystem functions and services used by millions of people. Yet, ongoing climate change is leading to an increase in frequency and magnitude of extreme climatic events in the tropics, which, in combination with other local human disturbances, is leading to unprecedented negative ecological consequences for tropical forests and coral reefs. Here, we provide an overview of how and where climate extremes are affecting the most biodiverse ecosystems on Earth and summarize how interactions between global, regional and local stressors are affecting tropical forest and coral reef systems through impacts on biodiversity and ecosystem resilience. We also discuss some key challenges and opportunities to promote mitigation and adaptation to a changing climate at local and global scales. This article is part of the theme issue 'Climate change and ecosystems: threats, opportunities and solutions'.

Effect of acute exposure to high ambient temperature on the thermal, metabolic and hygric physiology of a small desert bird

The intensity and frequency of extreme weather events, such as heat waves, are increasing as a consequence of global warming. Acute periods of extreme heat can be more problematic for wildlife than a chronic increase in mean temperature, to which animals can potentially acclimatise. Predicting effects of heat exposure requires a clear understanding of the capacity of individuals to respond to heat waves, so we examined the physiological response of a small desert bird, the zebra finch (Taeniopygia guttata), after acute previous exposure to high ambient temperature, simulating heatwave-like conditions. The standard physiology of the zebra finches was unaffected by prior exposure to heatwave-type conditions, suggesting that periodic exposure to heatwaves is unlikely to impact their longer-term day-to-day energy and water requirements. When finches were thermally challenged, prior experience of heatwave-like conditions did not impact overall body temperature and evaporative water loss, but birds previously experiencing high temperatures did reduce their metabolic heat production, and the variance in water loss and metabolism between individuals was significantly lower. This suggests that some individuals are more likely to become dehydrated if they have not had prior experience of high temperatures, and do not prioritise water conservation over thermoregulation. However, our observations overall suggest that acute periods of heat exposure do little to modify the general physiology of small birds, supporting the hypothesis that periodic extreme heat events may be more problematic for them than chronic warming.

Intra-Annual Variability in Responses of a Canopy Forming Kelp to Cumulative Low Tide Heat Stress: Implications for Populations at the Trailing Range Edge

Anthropogenic climate change is driving the redistribution of species at a global scale. For marine species, populations at trailing edges often live very close to their upper thermal limits and, as such, poleward range contractions are one of the most pervasive effects of ongoing and predicted warming. However, the mechanics of processes driving such contractions are poorly understood. Here, we examined the response of the habitat forming kelp, Laminaria digitata, to realistic terrestrial heatwave simulations akin to those experienced by intertidal populations persisting at the trailing range edge in the northeast Atlantic (SW England). We conducted experiments in both spring and autumn to determine temporal variability in the effects of heatwaves. In spring, heatwave scenarios caused minimal stress to L. digitata but in autumn all scenarios tested resulted in tissue being nonviable by the end of each assay. The effects of heatwave scenarios were only apparent after consecutive exposures, indicating erosion of resilience over time. Monthly field surveys corroborated experimental evidence as the prevalence of bleaching (an indication of physiological stress and tissue damage) in natural populations was greatest in autumn and early winter. Overall, our data showed that L. digitata populations in SW England persist close to their upper physiological limits for emersion stress in autumn. As the intensity of extreme warming events is likely to increase with anthropogenic climate change, thermal conditions experienced during periods of emersion will soon exceed physiological thresholds and will likely induce widespread mortality and consequent changes at the population level.

Relationship between the common brushtail possum (Trichosurus vulpecula) and tuart (Eucalyptus gomphocephala) tree decline in Western Australia

Forest canopy loss due to plant pathogens, insect or abiotic factors significantly alters habitat and resource availability for animals, which has flow-on effects for whole ecosystems. The tuart (Eucalyptus gomphocephala) has been in decline throughout its geographic range; this is likely associated with watertable and salinity changes, although a plant pathogen (Phytophthora multivora) has also been implicated. We examined the relative abundance of common brushtail possums (Trichosurus vulpecula) across 12 sites (each 0.72 ha) selected on the basis of the health of dominant tuart trees (six ‘healthy’ and six ‘declining’ sites). Habitat variables (understorey, tuart dimensions and density, tree hollows, tree-to-trap distance) and tuart tree health (crown loss, epicormic regrowth) were compared with possum abundance. Possums were detected at most sites. There was no significant difference between brushtail possum numbers at ‘healthy’ or ‘declining’ sites, although marginally more possums were recorded at declining sites (5.7 ± 1.5 (s.e.), n = 6 sites) compared with healthy sites (3.3 ± 0.7; Cohen’s effect size d = 0.80). Slightly higher abundance of possums was associated with sites that had a greater density of smaller-diameter but taller tuart trees. ‘Declining’ sites, with more epicormic regrowth and greater tree densities, may provide more palatable food resources for possums.

Physiological implications of climate change for a critically endangered Australian marsupial

Extreme weather events (e.g. heatwaves and droughts) can expose animals to environmental conditions outside of their zones of physiological tolerance, and even resistance, and impact long-term viability of populations and species. We examined the thermal and hygric physiology of the critically endangered western ringtail possum (Pseudocheirus occidentalis), a member of a family of marsupial folivores (Pseudocheiridae) that appear particularly vulnerable to environmental extremes. Basal metabolic rate and other standard physiological variables measured at an ambient temperature of 30°C conformed to values for other marsupials. At lower temperatures, body temperature decreased slightly, and metabolic rate increased significantly at 5°C. At higher temperatures, possums experienced mild hyperthermia and increased evaporative heat loss by licking rather than panting. Their point of relative water economy (–8.7°C) was more favourable than other pseudocheirid possums and the koala (Phascolarctos cinereus). We predict that western ringtail possums should tolerate low ambient temperatures well and be more physiologically tolerant of hot and dry conditions than common (Pseudocheirus peregrinus) and particularly green (Pseudochirops archeri) ringtail possums, and koalas. Our physiological data can be incorporated into mechanistic species distribution models to test our hypothesis that western ringtail possums should physiologically tolerate the climate of habitat further inland than their current distribution, and withstand moderate impacts of climate change in the south-west of Western Australia.

The Field Metabolic Rate, Water Turnover, and Feeding and Drinking Behavior of a Small Avian Desert Granivore During a Summer Heatwave

Global environmental change is leading to an increase in the frequency, intensity, and duration of extreme weather events, so effective environmental management requires an understanding not only of the physiological response of organisms to increased mean temperatures, but also to extreme environmental conditions. To determine the physiological consequences of heatwaves on energy and water balance of arid-adapted zebra finches (Taeniopygia guttata), we measured field metabolic rate and water turnover rate of wild, free-living finches during a heatwave (consecutive days of maximum ambient temperature of 40–45°C) and during a cooler period (maximum ambient temperature of 28°C) during a summer drought. To understand how birds accommodated their energy and water requirements, we also monitored feeding and drinking behavior of zebra finches at the study site on hot and cold days over 2.5 months during the same summer. Zebra finches can accommodate heatwaves without major impacts on field energy or water turnover, even when the heatwave is superimposed on high summer temperatures and long-term drought, so long as drinking water is available. In fact, cooler periods may pose a greater energetic challenge than heatwaves during drought, when food availability is limited, due to the increased thermoregulatory cost of maintaining a high body temperature against a thermal gradient. Zebra finches avoided or limited activity during the most thermally challenging periods of the day. Their pre-emptive feeding and drinking in preparation for hours of relative inactivity at high ambient temperature, together with a high body water content and reduced midday activity and metabolic heat production, enabled zebra finches to maintain body mass during a heatwave. Predicting upcoming periods of unfavorably high ambient temperature, together with a high body water content, may be essential for survival by desert birds of extreme ambient temperature during heatwaves.

Resilience of a harvested gastropod, Turbo militaris, to marine heatwaves

Marine heatwaves (MHW) are predicted to occur with increased frequency, duration and intensity in a changing climate, with pervasive ecological and socioeconomic consequences. While there is a growing understanding of the ecological impacts of warming and marine heatwaves, much less is known about how they influence the underlying physiology and health of species, and the nutritional properties of tissue. We evaluated the effects of different heatwave scenarios and ocean warming on the nutritional properties and immune health of the harvested gastropod Turbo militaris. Neither heatwave scenarios nor elevated temperatures had significant impacts on morphometrics, proximate composition or inorganic content of T. militaris. However, an increased moisture content and non-significant trends, such as elevated amount of lipids, and an increased number of hemocytes in the blood of T. militaris in the heatwave treatments were suggestive of mild stress. Overall, our study suggests that T. militaris is resilient to marine heatwaves and warming, although delayed, additive or synergistic stress responses cannot be ruled out. Understanding the possible effects of ocean warming and heatwaves on fisheries species could improve management actions to avoid species impacts, socioeconomic losses and negative effects to ecosystem service provision in a changing climate.

Carbon consequences of drought differ in forests that resprout

Prolonged drought and intense heat-related events trigger sudden forest die-off events and have now been reported from all forested continents. Such die-offs are concerning given that drought and heatwave events are forecast to increase in severity and duration as climate change progresses. Quantifying consequences to carbon dynamics and storage from die-off events are critical for determining the current and future mitigation potential of forests. We took stand measurements five times over 2+ years from affected and unaffected plots across the Northern Jarrah Forest, southwestern Australia, following an acute drought/heatwave in 2011. We found a significant loss of live standing carbon (49.3 t ha^-1 ), and subsequently a significant increase in the dead standing carbon pool by 6 months post-die-off. Of the persisting live trees, 38% experienced partial mortality contributing to the rapid regrowth and replenishment (82%-88%) of labile carbon pools (foliage, twigs, and branches) within 26 months. Such regrowth was not substantial in terms of net carbon changes within the timeframe of the study but does reflect the resprouting resilience of this forest type. Dead carbon generated by the die-off may persist for centuries given low fragmentation and decay rates resulting in low biogenic emission rates relative to other forest types. However, future fire may threaten persistence of both dead and live pools via combustion and mortality of live tissue and impaired regrowth capacity. Resprouting forests are commonly regarded as resilient systems, however, a changing climate could see vulnerable portions of forests become carbon sources rather than carbon sinks.

Widespread shifts in the coastal biota of northern California during the 2014-2016 marine heatwaves

During 2014-2016, severe marine heatwaves in the northeast Pacific triggered well-documented disturbances including mass mortalities, harmful algal blooms, and declines in subtidal kelp beds. However, less attention has been directed towards understanding how changes in sea surface temperature (SST) and alongshore currents during this period influenced the geographic distribution of coastal taxa. Here, we examine these effects in northern California, USA, with a focus on the region between Point Reyes and Point Arena. This region represents an important biogeographic transition zone that lies <150 km north of Monterey Bay, California, where numerous southern species have historically reached their northern (poleward) range limits. We report substantial changes in geographic distributions and/or abundances across a diverse suite of 67 southern species, including an unprecedented number of poleward range extensions (37) and striking increases in the recruitment of owl limpets (Lottia gigantea) and volcano barnacles (Tetraclita rubescens). These ecological responses likely arose through the combined effects of extreme SST, periods of anomalous poleward flow, and the unusually long duration of heatwave events. Prolonged marine heatwaves and enhanced poleward dispersal may play an important role in longer-term shifts in the composition of coastal communities in northern California and other biogeographic transition zones.

Global environmental consequences of twenty-first-century ice-sheet melt

Government policies currently commit us to surface warming of three to four degrees Celsius above pre-industrial levels by 2100, which will lead to enhanced ice-sheet melt. Ice-sheet discharge was not explicitly included in Coupled Model Intercomparison Project phase 5, so effects on climate from this melt are not currently captured in the simulations most commonly used to inform governmental policy. Here we show, using simulations of the Greenland and Antarctic ice sheets constrained by satellite-based measurements of recent changes in ice mass, that increasing meltwater from Greenland will lead to substantial slowing of the Atlantic overturning circulation, and that meltwater from Antarctica will trap warm water below the sea surface, creating a positive feedback that increases Antarctic ice loss. In our simulations, future ice-sheet melt enhances global temperature variability and contributes up to 25 centimetres to sea level by 2100. However, uncertainties in the way in which future changes in ice dynamics are modelled remain, underlining the need for continued observations and comprehensive multi-model assessments.