Lifeform indicators reveal large‐scale shifts in plankton across the North‐West European shelf

Increasing direct human pressures on the marine environment, coupled with climate‐driven changes, is a concern to marine ecosystems globally. This requires the development and monitoring of ecosystem indicators for effective management and adaptation planning. Plankton lifeforms (broad functional groups) are sensitive indicators of marine environmental change and can provide a simplified view of plankton biodiversity, building an understanding of change in lower trophic levels. Here, we visualize regional‐scale multi‐decadal trends in six key plankton lifeforms as well as their correlative relationships with sea surface temperature (SST). For the first time, we collate trends across multiple disparate surveys, comparing the spatially and temporally extensive Continuous Plankton Recorder (CPR) survey (offshore) with multiple long‐term fixed station‐based time‐series (inshore) from around the UK coastline. These analyses of plankton lifeforms showed profound long‐term changes, which were coherent across large spatial scales. For example, ‘diatom’ and ‘meroplankton’ lifeforms showed strong alignment between surveys and coherent regional‐scale trends, with the 1998–2017 decadal average abundance of meroplankton being 2.3 times that of 1958–1967 for CPR samples in the North Sea. This major, shelf‐wide increase in meroplankton correlated with increasing SSTs, and contrasted with a general decrease in holoplankton (dominated by small copepods), indicating a changing balance of benthic and pelagic fauna. Likewise, inshore‐offshore gradients in dinoflagellate trends, with contemporary increases inshore contrasting with multi‐decadal decreases offshore (approx. 75% lower decadal mean abundance), urgently require the identification of causal mechanisms. Our lifeform approach allows the collation of many different data types and time‐series across the NW European shelf, providing a crucial evidence base for informing ecosystem‐based management, and the development of regional adaptation plans.     

Phenological changes in intertidal con‐specific gastropods in response to climate warming

There is substantial evidence from terrestrial and freshwater systems of species responding to climate change through changes in their phenology. In the marine environment, however, there is less evidence. Using historic (1946–1949) and contemporary (2003–2007) data, collected from rocky shores of south‐west Britain, we investigated the affect of recent climate warming on the reproductive phenology of two con‐specific intertidal limpet grazers, with cool/boreal and warm/lusitanian centres of distribution. Reproductive development in the southern limpet, Patella depressa, has advanced, on average, 10.2 days per decade since the 1940s, with a longer reproductive season and more of the population reproductively active. The peak in the proportion of the population in advanced stages of gonad development was positively correlated with sea surface temperature (SST) in late spring/early summer, which has increased between the 1940s and 2000s. The advance in peak reproductive development of this species is double the average observed for terrestrial and freshwater systems and indicates, along with other studies, that marine species may be responding faster to climate warming. In contrast, the northern limpet, Patella vulgata, has experienced a delay in the timing of its reproductive development (on average 3.3 days per decade), as well as an increase in reproductive failure years and a reduction in the proportion of the population reaching advanced gonad stages. These results are the first to demonstrate a delay in the reproductive development of a cool‐temperate, winter spawner, towards cooler more favourable environmental conditions in response to climate warming. Such a delay in spawning will potentially lead to trophic miss‐matches, resulting in a rapid nonlinear decline of this species.     

Using palaeolimnological and limnological data to reconstruct the recent history of European lake ecosystems: introduction

1. As future climate change is expected to have a major impact on freshwater lake ecosystems, it is important to assess the extent to which changes taking place in freshwater lakes can be attributed to the degree of climate change that has already taken place. 2. To address this issue, it is necessary to examine evidence spanning many decades by combining long‐term observational data sets and palaeolimnological records. 3. Here, we introduce a series of case studies of seven European lakes for which both long‐term data sets and sediment records are available. Most of the sites have been affected by eutrophication and are now in recovery. 4. The studies attempt to disentangle the effects of climate change from those of nutrient pollution and conclude that nutrient pollution is still the dominant factor controlling the trophic state of lakes. 5. At most sites, however, there is also evidence of climate influence related in some cases to natural variability in the climate system, and in others to the trend to higher temperatures over recent decades attributed to anthropogenic warming. 6. More generally and despite some problems, the studies indicate the value of combining limnological and palaeolimnological records in reconstructing lake history and in disentangling the changing role of different pressures on lake ecosystems.     

Satellite‐based evidence for shrub and graminoid tundra expansion in northern Quebec from 1986 to 2010

Global vegetation models predict rapid poleward migration of tundra and boreal forest vegetation in response to climate warming. Local plot and air‐photo studies have documented recent changes in high‐latitude vegetation composition and structure, consistent with warming trends. To bridge these two scales of inference, we analyzed a 24‐year (1986–2010) Landsat time series in a latitudinal transect across the boreal forest‐tundra biome boundary in northern Quebec province, Canada. This region has experienced rapid warming during both winter and summer months during the last 40 years. Using a per‐pixel (30 m) trend analysis, 30% of the observable (cloud‐free) land area experienced a significant (P < 0.05) positive trend in the Normalized Difference Vegetation Index (NDVI). However, greening trends were not evenly split among cover types. Low shrub and graminoid tundra contributed preferentially to the greening trend, while forested areas were less likely to show significant trends in NDVI. These trends reflect increasing leaf area, rather than an increase in growing season length, because Landsat data were restricted to peak‐summer conditions. The average NDVI trend (0.007 yr^?1) corresponds to a leaf‐area index (LAI) increase of ~0.6 based on the regional relationship between LAI and NDVI from the Moderate Resolution Spectroradiometer. Across the entire transect, the area‐averaged LAI increase was ~0.2 during 1986–2010. A higher area‐averaged LAI change (~0.3) within the shrub‐tundra portion of the transect represents a 20–60% relative increase in LAI during the last two decades. Our Landsat‐based analysis subdivides the overall high‐latitude greening trend into changes in peak‐summer greenness by cover type. Different responses within and among shrub, graminoid, and tree‐dominated cover types in this study indicate important fine‐scale heterogeneity in vegetation growth. Although our findings are consistent with community shifts in low‐biomass vegetation types over multi‐decadal time scales, the response in tundra and forest ecosystems to recent warming was not uniform.     

Climate‐induced glacier and snow loss imperils alpine stream insects

Climate warming is causing rapid loss of glaciers and snowpack in mountainous regions worldwide. These changes are predicted to negatively impact the habitats of many range‐restricted species, particularly endemic, mountaintop species dependent on the unique thermal and hydrologic conditions found only in glacier‐fed and snow melt‐driven alpine streams. Although progress has been made, existing understanding of the status, distribution, and ecology of alpine aquatic species, particularly in North America, is lacking, thereby hindering conservation and management programs. Two aquatic insects – the meltwater stonefly (Lednia tumana) and the glacier stonefly (Zapada glacier) – were recently proposed for listing under the U.S. Endangered Species Act due to climate‐change‐induced habitat loss. Using a large dataset (272 streams, 482 total sites) with high‐resolution climate and habitat information, we describe the distribution, status, and key environmental features that limit L. tumana and Z. glacier across the northern Rocky Mountains. Lednia tumana was detected in 113 streams (175 sites) within Glacier National Park (GNP) and surrounding areas. The probability of L. tumana occurrence increased with cold stream temperatures and close proximity to glaciers and permanent snowfields. Similarly, densities of L. tumana declined with increasing distance from stream source. Zapada glacier was only detected in 10 streams (24 sites), six in GNP and four in mountain ranges up to ~600 km southwest. Our results show that both L. tumana and Z. glacier inhabit an extremely narrow distribution, restricted to short sections of cold, alpine streams often below glaciers predicted to disappear over the next two decades. Climate warming‐induced glacier and snow loss clearly imperils the persistence of L. tumana and Z. glacier throughout their ranges, highlighting the role of mountaintop aquatic invertebrates as sentinels of climate change in mid‐latitude regions.     

Ecosystem response to earlier ice break‐up date: Climate‐driven changes to water temperature,lake‐habitat‐specific production,and trout habitat and resource use

Climate warming has yielded earlier ice break‐up dates in recent decades for lakes leading to water temperature increases, altered habitat, and both increases and decreases to ecosystem productivity. Within lakes, the effect of climate warming on secondary production in littoral and pelagic habitats remains unclear. The intersection of changing habitat productivity and warming water temperatures on salmonids is important for understanding how climate warming will impact mountain ecosystems. We develop and test a conceptual model that expresses how earlier ice break‐up dates influence within lake habitat production, water temperatures and the habitat utilized by, resources obtained and behavior of salmonids in a mountain lake. We measured zoobenthic and zooplankton production from the littoral and pelagic habitats, thermal conditions, and the habitat use, resource use, and fitness of Brook Trout (Salvelinus fontinalis). We show that earlier ice break‐up conditions created a "resource‐rich" littoral–benthic habitat with increases in zoobenthic production compared to the pelagic habitat which decreased in zooplankton production. Despite the increases in littoral–benthic food resources, trout did not utilize littoral habitat or zoobenthic resources due to longer durations of warm water temperatures in the littoral zone. In addition, 87% of their resources were supported by the pelagic habitat during periods with earlier ice break‐up when pelagic resources were least abundant. The decreased reliance on littoral–benthic resources during earlier ice break‐up caused reduced fitness (mean reduction of 12 g) to trout. Our data show that changes to ice break‐up drive multi‐directional results for resource production within lake habitats and increase the duration of warmer water temperatures in food‐rich littoral habitats. The increased duration of warmer littoral water temperatures reduces the use of energetically efficient habitats culminating in decreased trout fitness.     

Continent‐scale global change attribution in European birds ‐ combining annual and decadal time scales

Species attributes are commonly used to infer impacts of environmental change on multiyear species trends, e.g. decadal changes in population size. However, by themselves attributes are of limited value in global change attribution since they do not measure the changing environment. A broader foundation for attributing species responses to global change may be achieved by complementing an attributes‐based approach by one estimating the relationship between repeated measures of organismal and environmental changes over short time scales. To assess the benefit of this multiscale perspective, we investigate the recent impact of multiple environmental changes on European farmland birds, here focusing on climate change and land use change. We analyze more than 800 time series from 18 countries spanning the past two decades. Analysis of long‐term population growth rates documents simultaneous responses that can be attributed to both climate change and land‐use change, including long‐term increases in populations of hot‐dwelling species and declines in long‐distance migrants and farmland specialists. In contrast, analysis of annual growth rates yield novel insights into the potential mechanisms driving long‐term climate induced change. In particular, we find that birds are affected by winter, spring, and summer conditions depending on the distinct breeding phenology that corresponds to their migratory strategy. Birds in general benefit from higher temperatures or higher primary productivity early on or in the peak of the breeding season with the largest effect sizes observed in cooler parts of species' climatic ranges. Our results document the potential of combining time scales and integrating both species attributes and environmental variables for global change attribution. We suggest such an approach will be of general use when high‐resolution time series are available in large‐scale biodiversity surveys.     

Climate‐driven habitat change causes evolution in Threespine Stickleback

Climate change can shape evolution directly by altering abiotic conditions or indirectly by modifying habitats, yet few studies have investigated the effects of climate‐driven habitat change on contemporary evolution. We resampled populations of Threespine Stickleback (Gasterosteus aculeatus) along a latitudinal gradient in California bar‐built estuaries to examine their evolution in response to changing climate and habitat. We took advantage of the strong association between stickleback lateral plate phenotypes and Ectodysplasin A (Eda) genotypes to infer changes in allele frequencies over time. Our results show that over time the frequency of low‐plated alleles has generally increased and heterozygosity has decreased. Latitudinal patterns in stickleback plate phenotypes suggest that evolution at Eda is a response to climate‐driven habitat transformation rather than a direct consequence of climate. As climate change has reduced precipitation and increased temperature and drought, bar‐built estuaries have transitioned from lotic (flowing‐water) to lentic (still‐water) habitats, where the low‐plated allele is favoured. The low‐plated allele has achieved fixation at the driest, hottest southernmost sites, a trend that is progressing northward with climate change. Climate‐driven habitat change is therefore causing a reduction in genetic variation that may hinder future adaptation for populations facing multiple threats.     

Climate‐change impacts on sandy‐beach biota: crossing a line in the sand

Sandy ocean beaches are iconic assets that provide irreplaceable ecosystem services to society. Despite their great socioeconomic importance, beaches as ecosystems are severely under‐represented in the literature on climate‐change ecology. Here, we redress this imbalance by examining whether beach biota have been observed to respond to recent climate change in ways that are consistent with expectations under climate change. We base our assessments on evidence coming from case studies on beach invertebrates in South America and on sea turtles globally. Surprisingly, we find that observational evidence for climate‐change responses in beach biota is more convincing for invertebrates than for highly charismatic turtles. This asymmetry is paradoxical given the better theoretical understanding of the mechanisms by which turtles are likely to respond to changes in climate. Regardless of this disparity, knowledge of the unique attributes of beach systems can complement our detection of climate‐change impacts on sandy‐shore invertebrates to add rigor to studies of climate‐change ecology for sandy beaches. To this end, we combine theory from beach ecology and climate‐change ecology to put forward a suite of predictive hypotheses regarding climate impacts on beaches and to suggest ways that these can be tested. Addressing these hypotheses could significantly advance both beach and climate‐change ecology, thereby progressing understanding of how future climate change will impact coastal ecosystems more generally.     

Temperature‐induced water stress in high‐latitude forests in response to natural and anthropogenic warming

The Arctic is particularly sensitive to climate change, but the independent effects of increasing atmospheric CO₂ concentration (pCO₂) and temperature on high‐latitude forests are poorly understood. Here, we present a new, annually resolved record of stable carbon isotope (δ¹³C) data determined from Larix cajanderi tree cores collected from far northeastern Siberia in order to investigate the physiological response of these trees to regional warming. The tree‐ring record, which extends from 1912 through 1961 (50 years), targets early twentieth‐century warming (ETCW), a natural warming event in the 1920s to 1940s that was limited to Northern hemisphere high latitudes. Our data show that net carbon isotope fractionation (Δ¹³C), decreased by 1.7‰ across the ETCW, which is consistent with increased water stress in response to climate warming and dryer soils. To investigate whether this signal is present across the northern boreal forest, we compiled published carbon isotope data from 14 high‐latitude sites within Europe, Asia, and North America. The resulting dataset covered the entire twentieth century and spanned both natural ETCW and anthropogenic Late Twentieth‐Century Warming (~0.7 °C per decade). After correcting for a ~1‰ increase in Δ¹³C in response to twentieth century pCO₂ rise, a significant negative relationship (r = ?0.53, P < 0.0001) between the average, annual Δ¹³C values and regional annual temperature anomalies is observed, suggesting a strong control of temperature on the Δ¹³C value of trees growing at high latitudes. We calculate a 17% increase in intrinsic water‐use efficiency within these forests across the twentieth century, of which approximately half is attributed to a decrease in stomatal conductance in order to conserve water in response to drying conditions, with the other half being attributed to increasing pCO₂. We conclude that annual tree‐ring records from northern high‐latitude forests record the effects of climate warming and pCO₂ rise across the twentieth century.     

Climate‐induced shift in hydrological regime alters basal resource dynamics in a wilderness river ecosystem

1. We integrated a 20‐year ecological data set from a sparsely inhabited, snowmelt‐dominated catchment with hydrologic models to predict the effects of hydrologic shifts on stream biofilm. 2. We used a stepwise multiple regression to assess the relationship between hydrology and biofilm ash‐free dry mass (AFDM) and chlorophyll‐a (chl‐a) under recent climate conditions. Biofilm AFDM was significantly related to the timing of peak streamflow, and chl‐a was significantly related to the timing of median streamflow. We applied these results to output from the variable infiltration capacity hydrologic model, which predicted hydrology under a baseline scenario (+0 °C) and a range of warming scenarios expected with climate change (+1, +2 or +3 °C). 3. When compared to the baseline, the results indicated that earlier peakflows predicted under warming scenarios may lead to earlier initiation of biofilm growth. This may increase biofilm AFDM during the summer by up to 103% (±29) in the +3 °C scenario. Moreover, interannual variability of AFDM was predicted to increase up to 300%. Average chl‐a during the summer increased by up to 90% (±15) in the +3 °C scenario; however, its response was not significantly different from baseline in most years. 4. Because hydrologic change may alter the temporal dynamics of biofilm growth, it may affect the seasonal dynamics of biofilm quality (i.e. chl‐a‐to‐AFDM ratio). The results indicated that hydrologic shifts may increase biofilm quality during the spring, but may decrease it during the summer. Thus, we provide evidence that predicted hydrologic shifts in snowmelt‐dominated streams may alter the quantity and quality of an important basal resource. However, the magnitudes of these predictions are likely to be affected by other environmental changes that are occurring with climate change (e.g. increased wildfire activity and stream warming).     

From global to regional and back again: common climate stressors of marine ecosystems relevant for adaptation across five ocean warming hotspots

Ocean warming ‘hotspots’ are regions characterized by above‐average temperature increases over recent years, for which there are significant consequences for both living marine resources and the societies that depend on them. As such, they represent early warning systems for understanding the impacts of marine climate change, and test‐beds for developing adaptation options for coping with those impacts. Here, we examine five hotspots off the coasts of eastern Australia, South Africa, Madagascar, India and Brazil. These particular hotspots have underpinned a large international partnership that is working towards improving community adaptation by characterizing, assessing and projecting the likely future of coastal‐marine food resources through the provision and sharing of knowledge. To inform this effort, we employ a high‐resolution global ocean model forced by Representative Concentration Pathway 8.5 and simulated to year 2099. In addition to the sea surface temperature, we analyse projected stratification, nutrient supply, primary production, anthropogenic CO₂‐driven ocean acidification, deoxygenation and ocean circulation. Our simulation finds that the temperature‐defined hotspots studied here will continue to experience warming but, with the exception of eastern Australia, may not remain the fastest warming ocean areas over the next century as the strongest warming is projected to occur in the subpolar and polar areas of the Northern Hemisphere. Additionally, we find that recent rapid change in SST is not necessarily an indicator that these areas are also hotspots of the other climatic stressors examined. However, a consistent facet of the hotspots studied here is that they are all strongly influenced by ocean circulation, which has already shown changes in the recent past and is projected to undergo further strong change into the future. In addition to the fast warming, change in local ocean circulation represents a distinct feature of present and future climate change impacting marine ecosystems in these areas.     

Climate‐dependent costs of reproduction: Survival and fecundity costs decline with length of the growing season and summer temperature

Costs of reproduction are expected to vary with environmental conditions thus influencing selection on life‐history traits. Yet, the effects of habitat conditions and climate on trade‐offs among fitness components remain poorly understood. For 2–5 years, we quantified costs of experimentally increased reproduction in two populations (coastal long‐season vs. inland short‐season) of two long‐lived orchids that differ in natural reproductive effort (RE; 30 vs. 75% fruit set). In both species, survival costs were found only at the short‐season site, whereas growth and fecundity costs were evident at both sites, and both survival and fecundity costs declined with increasing growing season length and/or summer temperature. The results suggest that the expression of costs of reproduction depend on the local climate, and that climate warming could result in selection favouring increased RE in both study species.     

Challenging a 15‐year‐old claim: The North Atlantic Oscillation index as a predictor of spring migration phenology of birds

Many migrant bird species that breed in the Northern Hemisphere show advancement in spring arrival dates. The North Atlantic Oscillation (NAO) index is one of the climatic variables that have been most often investigated and shown to be correlated with these changes in spring arrival. Although the NAO is often claimed to be a good predictor or even to have a marked effect on interannual changes in spring migration phenology of Northern Hemisphere breeding birds, the results on relations between spring migration phenology and NAO show a large variety, ranging from no, over weak, to a strong association. Several factors, such as geographic location, migration phase, and the NAO index time window, have been suggested to partly explain these observed differences in association. A combination of a literature meta‐analysis, and a meta‐analysis and sliding time window analysis of a dataset of 23 short‐ and long‐distance migrants from the constant‐effort trapping garden at Helgoland, Germany, however, paints a completely different picture. We found a statistically significant overall effect size of the NAO on spring migration phenology (coefficient = ?0.14, SE = 0.054), but this on average only explains 0%–6% of the variance in spring migration phenology across all species. As such, the value and biological meaning of the NAO as a general predictor or explanatory variable for climate change effects on migration phenology of birds, seems highly questionable. We found little to no definite support for previously suggested factors, such as geographic location, migration phenology phase, or the NAO time window, to explain the heterogeneity in correlation differences. We, however, did find compelling evidence that the lack of accounting for trends in both time series has led to strongly inflated (spurious) correlations in many studies (coefficient = ?0.13, SE = 0.019).     

Investigating the long‐term legacy of drought and warming on the soil microbial community across five European shrubland ecosystems

We investigated how the legacy of warming and summer drought affected microbial communities in five different replicated long‐term (>10 years) field experiments across Europe (EU‐FP7 INCREASE infrastructure). To focus explicitly on legacy effects (i.e., indirect rather than direct effects of the environmental factors), we measured microbial variables under the same moisture and temperature in a brief screening, and following a pre‐incubation at stable conditions. Specifically, we investigated the size and composition of the soil microbial community (PLFA) alongside measurements of bacterial (leucine incorporation) and fungal (acetate in ergosterol incorporation) growth rates, previously shown to be highly responsive to changes in environmental factors, and microbial respiration. We found no legacy effects on the microbial community size, composition, growth rates, or basal respiration rates at the effect sizes used in our experimental setup (0.6 °C, about 30% precipitation reduction). Our findings support previous reports from single short‐term ecosystem studies thereby providing a clear evidence base to allow long‐term, broad‐scale generalizations to be made. The implication of our study is that warming and summer drought will not result in legacy effects on the microbial community and their processes within the effect sizes here studied. While legacy effects on microbial processes during perturbation cycles, such as drying–rewetting, and on tolerance to drought and warming remain to be studied, our results suggest that any effects on overall ecosystem processes will be rather limited. Thus, the legacies of warming and drought should not be prioritized factors to consider when modeling contemporary rates of biogeochemical processes in soil.     

Temperature sensitivity of spring vegetation phenology correlates to within-spring warming speed over the Northern Hemisphere

The inter-annual shift of spring vegetation phenology relative to per unit change of preseason temperature, referred to as temperature sensitivity (days °C⁻¹), quantifies the response of spring phenology to temperature change. Temperature sensitivity was found to differ greatly among vegetation from different environmental conditions. Understanding the large-scale spatial pattern of temperature sensitivity and its underlying determinant will greatly improve our ability to predict spring phenology. In this study, we investigated the temperature sensitivity for natural ecosystems over the North Hemisphere (north of 30°N), based on the vegetation phenological date estimated from NDVI time-series data provided by the Advanced Very High Resolution Radiometer (AVHRR) and the corresponding climate dataset. We found a notable longitudinal change pattern with considerable increases of temperature sensitivity from inlands to most coastal areas and a less obvious latitudinal pattern with larger sensitivity in low latitude area. This general spatial variation in temperature sensitivity is most strongly associated with the within-spring warming speed (WWS; r = 0.35, p < 0.01), a variable describing the increase speed of daily mean temperature during spring within a year, compared with other factors including the mean spring temperature, spring precipitation and mean winter temperature. These findings suggest that the same magnitude of warming will less affect spring vegetation phenology in regions with higher WWS, which might partially reflect plants’ adaption to local climate that prevents plants from frost risk caused by the advance of spring phenology. WWS accounts for the spatial variation in temperature sensitivity and should be taken into account in forecasting spring phenology and in assessing carbon cycle under the projected climate warming.     

Human activities and climate variability drive fast‐paced change across the world's estuarine–coastal ecosystems

Time series of environmental measurements are essential for detecting, measuring and understanding changes in the Earth system and its biological communities. Observational series have accumulated over the past 2–5 decades from measurements across the world's estuaries, bays, lagoons, inland seas and shelf waters influenced by runoff. We synthesize information contained in these time series to develop a global view of changes occurring in marine systems influenced by connectivity to land. Our review is organized around four themes: (i) human activities as drivers of change; (ii) variability of the climate system as a driver of change; (iii) successes, disappointments and challenges of managing change at the sea‐land interface; and (iv) discoveries made from observations over time. Multidecadal time series reveal that many of the world's estuarine–coastal ecosystems are in a continuing state of change, and the pace of change is faster than we could have imagined a decade ago. Some have been transformed into novel ecosystems with habitats, biogeochemistry and biological communities outside the natural range of variability. Change takes many forms including linear and nonlinear trends, abrupt state changes and oscillations. The challenge of managing change is daunting in the coastal zone where diverse human pressures are concentrated and intersect with different responses to climate variability over land and over ocean basins. The pace of change in estuarine–coastal ecosystems will likely accelerate as the human population and economies continue to grow and as global climate change accelerates. Wise stewardship of the resources upon which we depend is critically dependent upon a continuing flow of information from observations to measure, understand and anticipate future changes along the world's coastlines.