Biological and Ecological Responses of Swordtip Squid Uroteuthis edulis to the 2023–2024 Marine Heatwave Off Sendai Bay, Northeastern Honshu, Japan

Under future climate scenarios, ocean temperatures that are presently extreme and qualify as marine heatwaves (MHW) are forecasted to increase in frequency and intensity, but little is known about the impact of these events on one of the most common paleoproxies, planktonic foraminifera. Planktonic foraminifera are globally ubiquitous, shelled marine protists. Their abundances and geochemistry vary with ocean conditions and fossil specimens are commonly used to reconstruct ancient ocean conditions. Planktonic foraminiferal assemblages are known to vary globally with sea surface temperature, primary productivity, and other hydrographic conditions, but have not been studied in the context of mid-latitude MHWs. For this study, the community composition and abundance of planktonic foraminifera were quantified for 2010-2019 along the Newport Hydrographic Line, a long-term monitoring transect at 44.6°N in the Northern California Current (NCC). Samples were obtained from archived plankton tows spanning 46 to 370 km offshore during annual autumn (August – October) cruises. Two MHWs impacted the region during this timeframe: the first during 2014-2016 and a second, shorter duration MHW in 2019. During the 2014-2016 MHW, warm water subtropical and tropical foraminifera species were more prevalent than the typical polar, subpolar, and transitional species common to this region. Cold water species were abundant again after the first MHW dissipated in late 2016. During the second, shorter-duration MHW in 2019, the assemblage consisted of a warm water assemblage but did not include tropical species. The foraminiferal assemblage variability correlated with changes in temperature and salinity in the upper 100 meters and was not correlated with distance offshore or upwelling. These results suggest that fossil foraminiferal assemblages from deep sea sediment cores may provide insight into the magnitude and frequency of past MHWs.

The spatio-temporal characteristics of the interannual variability and long-term trend of the marine heatwaves (MHWs) and related dynamic mechanisms in the western equatorial Indian Ocean (WEIO) are investigated using satellite observations. A prominent MHW hot spot is found in a region of the WEIO (48°E-54°E, 2°S-2°N), with a mean MHWs' intensity, duration, and frequency of 1.54°C, 13.33 days, and 1.97 times, respectively. MHWs in the hot spot region have significant interannual variability after removing the long-term trend, associated with Indo-Pacific major climate modes. In 1982/1983, 1983/1984, 1987/1988, 1997/1998, 2006/2007, 2009/2010, 2011/2012, 2012/2013, 2014/2015, 2015/2016, and 2019/2020, the MHWs occurred with longer duration, higher frequency, and more total days. These years correspond to a positive Indian Ocean Dipole, or an El Niño event, or both. The occurrence of MHWs accompanied by anomalous positive sea surface height suggests that oceanic planetary wave processes modulate MHWs in the WEIO. Westward-propagating downwelling equatorial Rossby waves triggered by anomalous equatorial easterly winds drive the convergence of warm upper-ocean water and weaken the upwelling of cool subsurface water, which favor anomalously warm sea surface temperature (SST) and the occurrence of MHWs. In addition, the westward-propagating off-equatorial downwelling Rossby waves in the southern tropical Indian Ocean also affect MHWs in the WEIO through the propagation and reflection of waves. The annual MHW frequency, duration, and total days in the hot spot region increase up to 1.56 times, 4.95 days, and 31.72 days per decade, respectively, related to the significant increase in mean SST under global warming.

Marine heat waves (MHWs) are recognized as pervasive drivers of impacts on marine species and ecosystems across the world; however, sub-Arctic areas that are rapidly losing seasonal sea-ice cover remain understudied. In this research, we examine a forty-year time series of MHW characteristics in the seasonally ice-covered James Bay region of the Canadian Inland Seas in central Canada. Through the period 1982 to 2021, we document the trends and investigate past MHW occurrences with respect to their driving processes. After only two MHW events during the early portion of the record (1982-1997), five events occurred in 1998 and signaled both an anomalous year and a step change in the region’s marine climatology. The new marine climate in the region is more variable with longer and more intense MHWs. Four or more MHWs occurred in each of 2001, 2005, 2010, 2012. Events in May and October 2021 lasted over a month in duration, with the former reaching intensities of between 2.5 and 3°C. MHW intensity was correlated with ice breakup date and positive Atlantic Multi-decadal Variability, which are suggested drivers of the increasing trends in sea surface temperatures. While the impacts of MHWs on marine and coastal ecosystems in the region remain unknown because of a lack of monitoring, the 1998 MHW intensification coincides with a massive decline in the region’s seagrass Zostera marina (eelgrass) ecosystem, which has been monitored since 1982. Given projections of more extreme MHWs under global warming and the sensitivity of marine species and ecosystems to warm water events, there is an urgent need to better tracks MHWs and investigate their role in shaping northern ecosystem changes.

Prolonged events of anomalously warm sea water temperature, or marine heatwaves (MHWs), have major detrimental effects to marine ecosystems and the world's economy. While frequency, duration and intensity of MHWs have been observed to increase in the global oceans, little is known about their potential occurrence and variability in estuarine systems due to limited data in these environments. In the present study we analyzed a novel data set with over three decades of continuous in situ temperature records to investigate MHWs in the largest and most productive estuary in the US: the Chesapeake Bay. MHWs occurred on average twice per year and lasted 11 days, resulting in 22 MHW days per year in the bay. Average intensities of MHWs were 3°C, with maximum peaks varying between 6 and 8°C, and yearly cumulative intensities of 72°C × days on average. Large co-occurrence of MHW events was observed between different regions of the bay (50–65%), and also between Chesapeake Bay and the Mid-Atlantic Bight (40–50%). These large co-occurrences, with relatively short lags (2–5 days), suggest that coherent large-scale air-sea heat flux is the dominant driver of MHWs in this region. MHWs were also linked to large-scale climate modes of variability: enhancement of MHW days in the Upper Bay were associated with the positive phase of Niño 1+2, while enhancement and suppression of MHW days in both the Mid and Lower Bay were associated with positive and negative phases of North Atlantic Oscillation, respectively. Finally, as a result of long-term warming of the Chesapeake Bay, significant trends were detected for MHW frequency, MHW days and yearly cumulative intensity. If these trends persist, by the end of the century the Chesapeake Bay will reach a semi-permanent MHW state, when extreme temperatures will be present over half of the year, and thus could have devastating impacts to the bay ecosystem, exacerbating eutrophication, increasing the severity of hypoxic events, killing benthic communities, causing shifts in species composition and decline in important commercial fishery species. Improving our basic understanding of MHWs in estuarine regions is necessary for their future predictability and to guide management decisions in these valuable environments.

Marine heatwaves (MHWs), characterized by multiple days of exceptionally elevated sea surface temperature (SST), have profound marine ecological impacts, but their effect on precipitation, particularly extreme rainfall over coastal regions, remains unknown. Using multi-platform observational data since 2000, here we show that SST gradients of MHW intensify surface wind speeds and drive downwind surface wind convergence and upward motions by enhancing vertical turbulent flux over the warm water. The induced anomalies lead to substantially increased local precipitation with spatial scale several hundreds of kilometers and temporally peaking one-day after the MHW. Furthermore, in global coastal regions, about 5%-25% of extreme rainfall over land (>99% wet-day) occurs in the downwind direction of nearby MHWs. Averaged land precipitation of the extreme rainfall events in the downwind direction of a strong MHW increases by 20%-30%, or 4-8 mm/day, from the amount without an influence from MHWs, exacerbating flood-related fatalities. Our finding identifies an impact of MHWs on coastal extreme events with important implications for affected communities, particularly given the projected increase in MHW intensity and frequency under greenhouse warming.

Analysis of ecosystem impacts from offshore wind (OSW) farm development has primarily focused on localized effects. However, in Eastern Boundary Current Upwelling Systems (EBUS) like the California Current, OSW farms can modify the intensity and spatial structure of wind-driven upwelling, inducing non-local (tens of kms away) changes to seawater temperature. Recent numerical modeling research determined that a hypothetical upper bound full buildout of OSW farms in central California could warm coastal waters through a reduction in upwelling. Here, we examine the sensitivity of coastal marine heatwaves (MHWs), which are prolonged extreme seawater temperatures that are among the greatest threats to marine ecosystems, to seawater temperature increases motivated by OSW-induced warming. Using a novel long-term coastal water temperature record spanning over four decades, we find that there is the potential for significant increases in MHW days, with individual MHWs becoming more intense and prolonged. Although the exact nature of OSW-induced changes to MHWs are uncertain, this is the first investigation into the potential impacts of OSW development on coastal MHWs, with important implications for marine ecosystems in EBUS globally where OSW is being considered. Despite the potential impacts, OSW remains a critical component to combat the much more pervasive issue of global climate change. • First study on impacts of offshore wind (OSW) farms on marine heatwaves (MHWs) • Sensitivity analysis of MHWs to OSW farm induced warming scenarios • Full buildout in central CA could increase MHW days, intensities, and durations • Non-local ecosystem impact of OSW in eastern boundary current upwelling systems

Depth- and season-resolved characteristics and drivers of marine heatwaves in the East Sea (Sea of Japan).

Extreme sea surface temperature (SST) events, such as marine heatwaves (MHWs) and marine cold spells (MCSs), severely affect warm water coral reefs. However, further study is required on their historical and future spatiotemporal patterns, driving mechanisms, and impacts in coral reef regions. This study analyzed the spatiotemporal patterns in MHWs/MCSs for the periods 1982–2022 and 2023–2070 using ten indices based on OISSTv2.1 and CMIP6 data, respectively, identified key MHW drivers via four machine learning methods (Random Forest, Extreme Gradient Boosting, Light Gradient Boosting Machine, and categorical boosting) and SHAP values (Shapley Additive Explanations), and then examined their relationship with coral coverage across ten global marine regions. Our results revealed that (1) MHWs are not only increasing in their average intensity but also becoming more extreme, while MCSs have declined. More MHW days are observed in regions like the Red Sea, the Persian Gulf, and the South Pacific Islands, with increases of up to 28 days per decade. (2) Higher-latitude coral reefs are experiencing more severe MHWs than equatorial regions, with up to 1.24 times more MHW days, emphasizing the urgent need to protect coral refuges. (3) MHWs are projected to occur nearly year-round by 2070 under scenario SSP5–8.5. The area ratio of MHWs to MCSs is expected to rise sharply from 2040 onward, reaching approximately 100-fold under the SSP2–4.5 scenario and 196-fold under the SSP5–8.5 scenario, particularly in the Marshall Islands and Caribbean Sea regions. (4) The coefficient of variation (CV) of annual temperature, annual ocean heat content, and monthly temperature were the top three factors driving MHW intensity. We emphasize that future MHW predictions should focus more on the CV of forecasting indicators rather than just the climate means. (5) Coral coverage exhibited post-mortality processes following MHWs, showing a strong negative correlation (r = −0.54, p < 0.01) with MHWs while demonstrating a significant positive correlation (r = 0.6, p < 0.01) with MCSs. Our research underscores the sustained efforts to protect and restore coral reefs amid escalating climate-induced stressors.

As the mean temperatures of the worlds oceans increase, it is predicted that marine heatwaves (MHWs) will occur more frequently and with increased severity. However, it has been shown that variables other than increases in sea water temperature have been responsible for MHWs. To better understand these mechanisms driving MHWs we have utilized atmospheric (ERA-Interim) and oceanic (OISST, AVISO) data to examine the patterns around southern Africa during coastal (in situ) MHWs. Nonmetric multidimensional scaling (NMDS) was first used to determine that the atmospheric and oceanic states during MHW are different from daily climatological states. Self-organizing maps (SOMs) were then used to cluster the MHW states into one of nine nodes to determine the predominant atmospheric and oceanic patterns present during these events. It was found that warm water forced onto the coast via anomalous ocean circulation was the predominant oceanic pattern during MHWs. Warm atmospheric temperatures over the subcontinent during onshore or alongshore winds were the most prominent atmospheric patterns. Roughly one third of the MHWs were clustered into a node with no clear patterns, which implied that they were not forced by a recurring atmospheric or oceanic state that could be described by the SOM analysis. Because warm atmospheric and/or oceanic temperature anomalies were not the only pattern associated with MHWs, the current trend of a warming earth does not necessarily mean that MHWs will increase apace; however, aseasonal variability in wind and current patterns was shown to be central to the formation of coastal MHWs, meaning that where climate systems shift from historic records, increases in MHWs will likely occur.

The effects of climate warming on ecosystem dynamics are widespread throughout the world's oceans. In the Northeast Pacific, large-scale climate patterns such as the El Niño/Southern Oscillation and Pacific Decadal Oscillation, and recently unprecedented warm ocean conditions from 2014 to 2016, referred to as a marine heatwave (MHW), resulted in large-scale ecosystem changes. Larval fishes quickly respond to environmental variability and are sensitive indicators of ecosystem change. Categorizing ichthyoplankton dynamics across marine ecosystem in the Northeast Pacific can help elucidate the magnitude of assemblage shifts, and whether responses are synchronous or alternatively governed by local responses to regional oceanographic conditions. We analyzed time-series data of ichthyoplankton abundances from four ecoregions in the Northeast Pacific ranging from subarctic to subtropical: the Gulf of Alaska (1981-2017), British Columbia (2001-2017), Oregon (1998-2017), and the southern California Current (1981-2017). We assessed the impact of the recent (2014-2016) MHW and how ichthyoplankton assemblages responded to past major climate perturbations since 1981 in these ecosystems. Our results indicate that the MHW caused widespread changes in the ichthyoplankton fauna along the coast of the Northeast Pacific Ocean, but impacts differed between marine ecosystems. For example, abundances for most dominant taxa were at all-time lows since the beginning of sampling in the Gulf of Alaska and British Columbia, while in Oregon and the southern California Current species richness increased as did abundances of species associated with warmer waters. Lastly, species associated with cold waters also increased in abundances close to shore in southern California during the MHW, a pattern that was distinctly different from previous El Niño events. We also found several large-scale, synchronized ichthyoplankton assemblage composition shifts during past major climate events. Current climate projections suggest that MHWs will become more intense and thus our findings can help project future changes in larval dynamics, allowing for improved ecosystem management decisions.

<p align="justify">Rapidly developing extreme events such as anomalously warm water events, known as Marine Heat Waves (MHWs), have received considerable attention in the past few years due to the significant impact they have on regional ecosystems and socioeconomic activity. The Peruvian Coastal Upwelling System (PCUS), one of the most productive ecosystem in the world in terms of fisheries, is highly exposed to climate variability in particular because of its geographic location close to the equator, and the influence of the subtropical high pressure cell variability.</p><p align="justify">The PCUS is highly influenced by El Niño events, which have been intensively studied, and whose variability is related to the longest and most intense MHWs in the region. However the very visible El Niño events probably overshadowed the MHWs of shorter duration that also have an important impact on the coastal environment as they can often go with other extreme events such as nearshore hypoxia. To date, a census of MHWs of shorter duration (less than 30 days) is lacking in the region.</p><p><span>Here, we investigate the characteristics (spatial variability, frequency, intensity and duration) and evolution of such MHWs in the South Tropical Eastern Pacific, with a focus on the PCUS coastal area where the ecological vulnerability is higher. Several sea surface temperature satellite products are compared to test the sensitivity of the results. </span></p><p><span>The distinction between El Niño events and regular MHWs has a major impact on the statistical distribution of MHWs properties in the South Equatorial and South Tropical Eastern Pacific as well as on their evolution over the last 35 years. First results indicate that in the equatorial region and along the Peruvian coast, fewer MHWs and of shorter duration are observed north than south of 15°S. The observed trend is an increase of MHWs occurrences, duration and intensity in the South Tropical Eastern Pacific over the last 35 years, with the exception of the coastal region off Peru where </span><span>t</span><span>he trend in occurrences and duration is the same </span><span>but </span><span>the average temperature anomaly associated to MHWs has decreased. It also seems that there is no apparent preferential season for the occurrence of MHWs. A study of the possible drivers is performed in an attempt to disentangle the role of the local (wind stress, heat fluxes) and remote (equatorial wave activity) forcing. </span></p>

The West African climate system is highly sensitive to oceanic conditions in the Gulf of Guinea (GG), where rising sea surface temperatures (SSTs) and marine heatwaves (MHWs) are emerging as key indicators of regional climate change. This study analyses the relationship between MHW during the monsoon period and rainfall in West Africa using 30‐year data (May–October) of daily SST and precipitation. Based on the SST dataset. MHW intensities allowed to delineate the oceanic zones of their occurrences. The results show that these events have enhanced over the last decade along the northern coast of the GG and at the equator. Different classes are defined in each oceanic area defined. The high intensities of the MHWs of the different classes are located in the upwelling zone along the northern coast of GG. The analysis of the cumulative annual rainfall shows that the wettest regions are situated in the western and eastern parts of the Guinean zone of West Africa. It’s interannual trend is not significant, even if there is a break in 2018. The first modes of the relationships between each class of MHWs and rainfall show significant correlations between MHWs and rainfall of the coastal area and in the Sahelian zone. Most of the MHWs at the northern coast of the GG and in the tropical Atlantic cold tongue area have a positive influence on rainfall. All MHW events associated with rainfall represent about half of the MHW events that occur at the northern coast of the GG. For the Atlantic cold tongue area, the percentage of MHW concomitant with rainfall is about two‐third. A rainfall deficit is observed in the Sahelian zone during MHW events. This indicates that the onset of a rainfall deficit north of 10°N and an excess to the south coincides with the warming of the surface waters of the GG. This study is a first step to understand the impact of MHWs on climate, and their relationships with weather catastrophic extreme events.

Marine foundation species underpin some of the world's most diverse ecosystems but they are increasingly threatened by intensification of marine heatwaves (MHWs). Where MHWs exceed critical thermal maxima (CTmax), increased mortality and population declines can occur. CTmax is increasingly used to assess MHW population vulnerability but studies estimating CTmax across species, range edges and thermal histories in a comparable manner remain lacking. We determined the impact of MHWs on subsequent CTmax estimates of matched cool/warm affinity pairs of marine foundation species (kelp, seagrass and bivalves) in the Western English Channel. Following a 4‐week MHW simulation, individuals were subjected to a CTmax trial, where temperatures were raised by 2°C day−1 until physiological end points were reached. We found no positive effect of MHWs on CTmax but clear negative impacts were observed for some groups of foundation species. Increased MHW intensity had a stepwise negative impact on the physiology of both warm (Laminaria ochroleuca) and cool water (L. digitata) kelp species that manifested in significant reductions in CTmax. Surprisingly, this was most marked in the warm water species, which runs opposite to the assumed safety of leading‐edge populations. The physiology of warm (Zostera noltii) and cool (Z. marina) seagrasses was negatively impacted by increasing MHW intensity but no significant decrease in CTmax was observed. Both bivalve species (Mytilus edulis and Magallana gigas) showed marked resistance to exposure to MHWs, which was unexpected given the observed vulnerability of these species to stressful summertime conditions. Our results show pre‐exposure to realistic MHWs can influence CTmax values but generalities are difficult to make across groups or based on assumed thermal safety margins. We show CTmax is a labile trait and exposure to MHWs, can erode the resilience of an individual or population to subsequent thermal challenges. This leaves uncertainty within frameworks built to understand where and when MHWs will be most impactful. Further experimentation across a wider range of species and thermal challenges is needed to better understand the dynamic nature of CTmax and field validation is needed to determine the responses of individuals and populations within complex natural systems. Read the free Plain Language Summary for this article on the Journal blog.

Marine heatwaves (MHWs), or prolonged periods of anomalously warm sea water temperature, have been increasing in duration and intensity globally for decades. However, there are many coastal, oceanic, polar, and sub-surface regions where our ability to detect MHWs is uncertain due to limited high quality data. Here we investigate the effect that short time series length, missing data, or linear long-term temperature trends may have on the detection of MHWs. We show that MHWs detected in time series as short as 10 years did not have durations or intensities appreciably different from events detected in a standard 30 year long time series. We also show that the output of our MHW algorithm for time series missing less than 25% data did not differ appreciably from a complete time series, and that the level of allowable missing data could cautiously be increased to 50% when gaps were filled by linear interpolation. Finally, linear long-term trends of 0.10°C/decade or greater added to a time series caused larger changes (increases) to the count and duration of detected MHWs than shortening a time series to 10 years or missing more than 25% of the data. The long-term trend in a time series has the largest effect on the detection of MHWs and has the largest range in added uncertainty in the results. Time series length has less of an effect on MHW detection than missing data, but adds a larger range of uncertainty to the results. We provide suggestions for best practices to improve the accuracy of MHW detection with sub-optimal time series and show how the accuracy of these corrections may change regionally.

BackgroundOngoing global ocean warming and a recent increase in the frequency and duration of marine heatwaves have demonstrably impacted marine ecosystems. Growing evidence points to both short- and long-term biological changes, across several levels of organization. While range shifts are among the predicted responses, few studies are focused solely on documenting such changes. Here we report ecological changes in response to marine heatwaves across multiple taxa in the eastern Pacific from central California to Baja California.MethodsSea surface temperature data from two estuaries and one coastal site were analyzed to define the number, duration, and intensity of marine heatwaves occurring in central and southern California from 2013 to 2018. Long-term monitoring programs and short-term research projects in coastal and estuarine ecosystems serendipitously collected specimens or photographs of extralimital species from central California to the Baja California Peninsula. Spatial and temporal sampling protocols and the targeted species for six unrelated programs varied greatly, from annual to monthly at both fixed and variable locations. In addition, anomalous occurrences were reported to staff at local and regional marine and estuarine protected areas and noted in local news and social media outlets. Anomalous range detections were categorized as range expansions and extensions, reappearances, abundance increases, shifts into new habitats, and range contractions.ResultsMultiple marine heatwaves occurred from 2014 to 2018, peaking in 2015. Marine heatwaves were more intense and longer in the estuaries, with a maximum duration of 109 days in 2015. We observed 29 species that had responded to the warm water anomalies of 2014–2018 along the eastern Pacific Ocean between central California and the Baja California Peninsula: 7 expansions, 2 extensions, 10 reappearances, 7 increases, 2 shifts into new habitats, and 1 apparent contraction. These shifts included algae, invertebrates and fishes. Twenty species were observed by professional biologists involved both in long-term monitoring programs and short-term studies, 6 by amateur naturalists as part of community-based science programs in the field, and 3 through a combination of all three.ConclusionsIncreased warm waters, sustained for an unprecedented 4 of 5 years, facilitated the northward redistribution of multiple species from several taxonomic groups. Species shifting northward were from warm-temperate and subtropical ecosystems to the south. In the absence of programs designed to detect range shifts, we must rely on the serendipitous observations of biologists conducting both long-term monitoring and short-term research, and the growing wealth of information from community-based science programs made available via online databases.