Effects Of Multiple Stressors Research Articles

Global Swimways for the conservation of migratory freshwater fishes

AbstractAnthropogenic activities have severely degraded the ecological integrity of global freshwater systems. Migratory freshwater fishes are especially threatened by the cumulative effects of multiple stressors and fragmentation, particularly those that impede access to critical habitats. To stimulate the conservation and protection of these species, we propose a “Global Swimways” program to identify rivers that support the migration routes of biologically and/or socioeconomically important freshwater fishes. We test the utility of the International Union for Conservation of Nature Red List data to support the identification of Global Swimways and present case study regions containing rivers with either high species richness (west‐central Africa and Southeast Asia), high numbers of threatened species (Eastern Europe and Central Asia), or multiple endemic species (the Rift Valley lakes in East Africa). We hope the Global Swimways program will provide metrics that can be used to identify rivers requiring increased protection or restoration, track trends, and stimulate the greater inclusion of migratory freshwater fishes in global policy mechanisms.Front Ecol Environ 2022;

Variations in cost of transport and their ecological consequences: a review.

Movement is essential in the ecology of most animals, and it typically consumes a large proportion of individual energy budgets. Environmental conditions modulate the energetic cost of movement (cost of transport, COT), and there are pronounced differences in COT between individuals within species and across species. Differences in morphology affect COT, but the physiological mechanisms underlying variation in COT remain unresolved. Candidates include mitochondrial efficiency and the efficiency of muscle contraction-relaxation dynamics. Animals can offset increased COT behaviourally by adjusting movement rate and habitat selection. Here, we review the theory underlying COT and the impact of environmental changes on COT. Increasing temperatures, in particular, increase COT and its variability between individuals. Thermal acclimation and exercise can affect COT, but this is not consistent across taxa. Anthropogenic pollutants can increase COT, although few chemical pollutants have been investigated. Ecologically, COT may modify the allocation of energy to different fitness-related functions, and thereby influence fitness of individuals, and the dynamics of animal groups and communities. Future research should consider the effects of multiple stressors on COT, including a broader range of pollutants, the underlying mechanisms of COT and experimental quantifications of potential COT-induced allocation trade-offs.

The effects of a half century of warming and fire exclusion on montane forests of the Klamath Mountains, California, USA

AbstractClimate warming and altered disturbance regimes are changing forest composition and structure worldwide. Given that species often exhibit individualistic responses to change, making predictions about the cumulative effects of multiple stressors across environmental gradients is challenging, especially in diverse communities. For example, warming temperatures are predicted to drive species upslope, whereas fire exclusion promotes the expansion of species at lower elevations where fire was historically frequent. We resampled 148 vegetation plots to assess 46 years (1969–2015) of species and community‐level response to warming and fire exclusion in a topographically complex landscape in the Klamath Mountains, California, USA, a diverse region that served as a climate refugia throughout the Holocene. We compared cover and assessed change in the elevational distributions of 12 conifer species at different life stages (i.e., seedlings, saplings, canopy). We observed consistent but non‐significant shifts upward in elevation for eight species, and a significant shift upward for one species, all of which were far less than expectations based on recent warming. Six species declined in total cover and another five declined in at least one life stage, whereas the drought‐ and fire‐intolerant Abies concolor increased by 30.7%. The largest declines were at lower elevations in drought‐tolerant, early‐seral species (Pinus lambertiana and Pinus ponderosa) and at higher elevations for the shade‐tolerant Abies magnifica var. shastensis and the regionally rare Abies lasiocarpa. Regionally rare (Picea engelmannii) and endemic (Picea breweriana) species had reductions in early life stages, portending future declines. Multivariate analyses revealed a high degree of inertia with a minor, but significant, shift in composition and a slight decrease in species turnover along the elevation gradient driven by the expansion of A. concolor. Our results indicate that most species are declining, especially at lower and mid‐elevations where fire exclusion has increased the cover of shade‐tolerant species and reduced the recruitment for fire‐adapted species. Collectively, declines in most species, insufficient upward movement to track warming, reductions in drought‐ and fire‐tolerant early‐seral species, and an increase in a single, shade‐tolerant species will leave these communities maladapted to projected climate scenarios and questions the potential for future climate refugia in this region.

A systematic review and meta-analysis of the relationship between farm management, water quality and pathogen outbreaks in tilapia culture.

A systematic review and meta-analysis of on farm management and water quality as risk factors triggering pathogen outbreaks in tilapia culture is presented. A total of 121 papers from 28 countries, 37 devoted to management and 84 to water quality associated with the presence of pathogens in tilapia culture were analysed. Most of research has been made on ponds, focusing on bacteria and metazoans. Meta-analysis reveals the proportion of research showing statistical inferences between management (34%), water quality (38% for bacteria and 16.2% for metazoans) and pathogen outbreaks. The most cited parameters related to pathogens outbreaks were temperature (>30°C), dissolved oxygen (<5.0mg/L), pH (<8.0) and ammonia (1.0 >mg/L) 65, 38, 32 and 34 papers, respectively. However, statistical inference was <20%. Meta-analysis reveals tendencies between high temperatures (30-35°C), low dissolved oxygen (<5mg/L) and high NH3 (1-5mg/L) with pathogen outbreaks. Despite the knowledge about the relationship between management and water quality as factors for pathogen effects, most information is descriptive and empirical. Future research on tilapia culture outbreaks should be focused on the effects of multiple stressors affecting tilapia pathogen outbreaks, thereby generating strategies to prevent diseases and financial losses.

Edaphic stress interactions: Important yet poorly understood drivers of plant production in future climates

Most terrestrial plants experience multiple edaphic (i.e. soil-related) stresses concurrently. Interactions among edaphic stresses may be characterized by dominance of one stress over others, neutral interactions whose effects are additive, mitigating interactions in which the effects of multiple stresses are less than additive, potentiating interactions in which the effects of multiple stresses are greater than additive, and dynamic equilibria in which plant responses seek to minimize all stresses concurrently. Existing theoretical paradigms, notably the Law of the Minimum and the Multiple Limitation Hypothesis, do not adequately account for interactions of edaphic stresses. Reduced growth resulting from edaphic stress is itself an important modulator of stress interactions by reducing resource demand as well as reducing soil resource capture. Root adaptations to one edaphic stress may either mitigate or potentiate other edaphic stresses, as evidenced by the examples of root architectural tradeoffs for water and P capture, in contrast to root architectural synergies for water and nitrate capture. In high-input agroecosystems, edaphic stress complexes of global importance include mechanical impedance/poor soil structure/drought stress, and salinity/drought stress. In low-input agroecosystems, globally important edaphic stress complexes include drought and low soil P availability, as well as the acid soil complex, characterized by toxicity of Al and possibly Mn, combined with low availability of P, K, Ca, and Mg. Global climate change is likely to exacerbate edaphic stress, by increasing the severity and frequency of drought and flooding, accelerating soil degradation, and altering plant phenology. Many of the edaphic stresses exacerbated by global climate change have potentiating interactions with each other, which is likely to make them more harmful than anticipated from their direct effects. Edaphic stresses linked to climate change are likely to have severe impacts in developing nations, which generally have more problematic soils and more limited management options than developed nations. The potential benefits of CO2 fertilization for plants in future climates may be mitigated by edaphic stress. Edaphic stress interactions are a challenge for crop breeding programs, because resistance to edaphic stress is generally quantitative and may display fitness tradeoffs with other edaphic stresses. Germplasm evaluation in farmer’s conditions, ideotype breeding, and deployment of root phenotypes with utility for multiple edaphic stresses, such as long, dense root hairs, and root cortical aerenchyma, would be helpful in this context. Interactions among edaphic stresses are key drivers of plant growth in the majority of global soils. Improved understanding of edaphic stress interactions is needed to develop the more resilient, stress tolerant crops and cropping systems that are urgently needed in global agriculture.

The impact of cumulative stressor effects on uncertainty and ecological risk

To enable environmental management actions to be more effectively prioritized, cumulative effects between multiple stressors need to be accounted for in risk-assessment frameworks. Ecological risk and uncertainty are generally high when multiple stressors occur. In the face of high uncertainty, transparent communication is essential to inform decision-making. The impact of stressor interactions on risk and uncertainty was assessed using generalized linear models for additive and multiplicative effect of six anthropogenic stressors on the abundance of estuarine macrofauna across New Zealand. Models that accounted for multiplicative stressor interactions demonstrated that non-additive effects dominated, had increased explanatory power (6 to 73 % relative increase between models), and thereby reduced the risk of unexpected ecological responses to stress. Secondly, 3D-plots provide important insights in the direction, magnitude and gradients of change, and aid transparency and communication of complex stressor effects. Notably, small changes in a stressor can cause a disproportionally steep gradient of change for a synergistic effect where the tolerance to stressors are lost, and would invoke precautionary management. 3D-plots were able to clearly identify directional shifts where the nature of the interaction changed from antagonistic to synergistic along increasing stressor gradients. For example, increased nitrogen load and exposure caused a shift from positive to negative effect on the abundance of a deposit-feeding polychaete (Magelona). Assessments relying on model coefficient estimates, which provide one effect term, could not capture the complexities observed in 3D-plots and are at risk of mis-identifying interaction types. Finally, visualising model uncertainty demonstrated that although error terms were higher for multiplicative models, they better captured the uncertainty caused by data availability. Together, the steep gradients of change identified in 3D-plots and the higher uncertainty in model predictions in multiplicative models urges more conservative limits to be set for management that account for risk and uncertainty in multiple stressor effects.

Rapidly declining body size in an insectivorous bat is associated with increased precipitation and decreased survival.

Reduced food availability is implicated in declines in avian aerial insectivores, but the effect of nutritional stress on mammalian aerial insectivores is unclear. Unlike birds, insectivorous bats provision their young through lactation, which might protect nursing juveniles when prey availability is low but could increase the energetic burden on lactating females. We analyzed a 15-year capture-mark-recapture data set from 5312 individual little brown myotis (Myotis lucifugus) captured at 11 maternity colonies in northwestern Canada, to test the hypothesis that nutritional stress is impacting these mammalian aerial insectivores. We used long-bone (forearm [FA]) length as a proxy for relative access to nutrition during development, and body mass as a proxy for access to nutrition prior to capture. Average FA length and body mass both decreased significantly over the study period in adult females and juveniles, suggesting decreased access to nutrition. Effect sizes were very small, similar to those reported for declining body size in avian aerial insectivores. Declines in juvenile body mass were only observed in individuals captured in late summer when they were foraging independently, supporting our hypothesis that lactation provides some protection to nursing young during periods of nutritional stress. Potential drivers of the decline in bat size include one or both of (1) declining insect (prey) abundance, and (2) declining prey availability. Echolocating insectivorous bats cannot forage effectively during rainfall, which is increasing in our study area. The body mass of captured adult females and juveniles in our study was lower, on average, after periods of high rainfall, and higher after warmer-than-average periods. Finally, survival models revealed a positive association between FA length and survival, suggesting a fitness consequence to declines in body size. Our study area has not yet been impacted by bat white-nose syndrome (WNS), but research elsewhere has suggested that fatter bats are more likely to survive infection. We found evidence for WNS-independent shifts in the body size of little brown myotis, which can inform studies investigating population responses to WNS. More broadly, the cumulative effects of multiple stressors (e.g., disease, nutritional stress, climate change, and other pressures) on mammalian aerial insectivores require urgent attention.

Perception and consideration of cumulative effects and multiple stressors by marine managers in Canada

The cumulative effects of multiple stressors are a pressing global concern for marine ecosystems. The effectiveness of marine management can be improved by considering three key elements that can affect their impacts: stressor interaction types, non-linear stressor–effect relationships, and ecosystem tipping points. Little is known about the degree to which cumulative effects, or these key elements, are considered in marine management in Canada. We surveyed Canadian federal government managers involved in managing either marine conservation areas or commercial fisheries, and asked (1) if they currently assess cumulative effects in decision-making, (2) if so, how and which elements are considered, and (3) the perceived importance of considering the three key elements. We also compared approaches among federal departments, management type, oceans, experience levels, and position types. We found that most managers (84%, n = 80) consider cumulative effects in decision-making. Responses clustered into either a structured approach, which included using an assessment framework and considering the three key elements of cumulative effects, or an intuitive approach, characterized by the absence of a formal framework or consideration of key elements. Neither was strongly linked with demographic categories. Despite most managers (97%, n = 37) believing that the three key elements of cumulative effects are important to consider, only 21% actually did so in decision-making. This discrepancy appears to be underpinned by barriers such as a lack of guidelines for assessing cumulative effects and data quality, quantity, and availability. We provide recommendations to overcome these challenges.

Warming lowers critical thresholds for multiple stressor–induced shifts between aquatic primary producers

In aquatic ecosystems, excessive nutrient loading is a global problem that can induce regime shifts from macrophyte- to phytoplankton-dominated states with severe consequences for ecosystem functions. Most agricultural landscapes are sites of nutrient and pesticide loading, which can interact with other stressors (e.g., warming) in additive, antagonistic, synergistic or reversed forms. The effects of multiple stressors on the resilience of macrophyte-dominated states and on critical thresholds for regime shifts are, however, unknown. We test the effects of individual and combined stressors of warming, nitrate, and various pesticides typically found in agricultural run-off (ARO) on the growth of macrophytes, periphyton, and phytoplankton in microcosms. We applied a one-level replicated design to test whether ARO induces a regime shift and a multifactorial dose–response design to model stressor thresholds and disentangle stressor interactions along a gradient. The individual stressors did not induce a regime shift, but the full ARO did. Nitrate and pesticides acted synergistically, inducing a shift with increasing phytoplankton biomass and decreasing macrophyte biomass. Warming amplified this effect and lowered critical thresholds for regime shifts. Shallow aquatic ecosystems in agricultural landscapes affected by global warming thus increasingly risk shifting to a turbid, phytoplankton-dominated state, and negatively impacting ecosystem service provisioning. Multiple stressor interactions must be considered when defining safe operating spaces for aquatic systems.

Individual and combined effects of diuron and light reduction on marine microalgae

Coastal ecosystems such as those in the Great Barrier Reef (GBR) lagoon, are exposed to stressors in flood plumes including low light (caused by increased turbidity) and agricultural pesticides. Photosystem II (PSII)-inhibiting herbicides are the most frequently detected pesticides in the GBR lagoon, but it is not clear how their toxicity to phototrophic species depends on light availability. This study investigated the individual and combined effects of PSII-inhibiting herbicide, diuron, and reduced light intensity (as a proxy for increased turbidity) on the marine diatom, Phaeodactylum tricornutum. Effective quantum yield (EQY) and cell density were measured to calculate responses relative to the controls over 72-h, in tests with varying stressor intensities. Individually, diuron concentrations (0.1–3 μg l−1) were not high enough to significantly reduce growth (cell density), but led to decreased EQY; while, low light generally led to increased EQY, but only reduced growth at the lowest tested light intensity (5 μmol photons m−2 s−1) after 48-hours. P. tricornutum was less affected by diuron when combined with low light scenarios, with increased EQY (up to 163% of the controls) that was likely due to increased electron transport per photon, despite lesser available photons at this low light intensity. In contrast, growth was completely inhibited relative to the controls when algae were simultaneously exposed to the highest stressor levels (3 μg l−1 diuron and 5 μmol photons m−2 s−1). This study highlights the importance of measuring more than one biological response variable to capture the combined effects of multiple stressors. Management of water quality stressors should consider combined impacts rather than just the impacts of individual stressors alone. Reducing suspended sediment and diuron concentrations in marine waters can decrease harmful effects and bring synergistic benefits to water quality.

Mapping the vulnerability of indigenous fruit trees to environmental change in the fragile savannah ecological zone of Northern Ghana

Following the incidence of environmental change globally and its negative consequences on livelihoods of local populations, vulnerability assessment has become central to mitigation and adaptation response in the global south. However, researches on vulnerability to climate change in the African continent have seldom focused on Indigenous Fruit Trees (IFTs) although they are an essential part of the strategic forest resources and livelihood systems of local communities. This paper explores the vulnerability of two IFTs, shea (Vitellaria paradoxa) and dawadawa (Parkia biglobosa) to climatic and other stressors that are not directly linked to climate change in rural Ghana and the implications for planning. The paper analyzed vulnerability from farmer perspectives elicited through a mixed study design involving the use of Participatory Rural Appraisal (PRA) methods and a household survey. The results reveal that IFTs are highly vulnerable to drought, rainstorms, bushfires and charcoal production and less vulnerable to heavy precipitation, flash floods and sand mining. Such vulnerability arising from the combined effects of multiple stressors has led to a decreasing trend in production and yields of IFTS over the past few decades, adversely affecting livelihoods of rural women and households. To reduce vulnerability, it is an imperative to promote Environmental Change Adaptation Planning (ECAP) that prioritizes conservation and propagation of IFTs, and diversification of rural livelihoods.

Responses to simultaneous anthropogenic and biological stressors were mixed in an experimental saltmarsh ecosystem

Coastal ecosystems are essential for absorbing and bouncing back from the impacts of climate change, yet accelerating climate change is causing anthropogenically-derived stressors in these ecosystems to grow. The effects of stressors are more difficult to foresee when they act simultaneously, however, predicting these effects is critical for understanding ecological change. Spartina alterniflora (Spartina), a foundational saltmarsh plant key to coastal resilience, is subject to biological stress such as herbivory, as well as anthropogenic stress such as chemical pollution. Using saltmarsh mesocosms as a model system in a fully factorial experiment, we tested whether the effects of herbivory and two chemicals (oil and dispersant) were mediated or magnified in combination. Spartina responded to stressors asynchronously; ecophysiology responded negatively to oil and herbivores in the first 2–3 weeks of the experiment, whereas biomass responded negatively to oil and herbivores cumulatively throughout the experiment. We generally found mixed multi-stressor effects, with slightly more antagonistic effects compared to either synergistic or additive effects, despite significant reductions in Spartina biomass and growth from both chemical and herbivore treatments. We also observed an indirect positive effect of oil on Spartina, via a direct negative effect on insect herbivores. Our findings suggest that multi-stressor effects in our model system, 1) are mixed but can be antagonistic more often than expected, a finding contrary to previous assumptions of primarily synergistic effects, 2) can vary in duration, 3) can be difficult to discern a priori, and 4) can lead to ecological surprises through indirect effects with implications for coastal resilience. This leads us to conclude that understanding the simultaneous effects of multiple stressors is critical for predicting foundation-species persistence, discerning ecosystem resilience, and managing and mitigating impacts on ecosystem services.

Interactive effects of multiple stressors on the physiological performance of the invasive mussel Mytilus galloprovincialis

The invasive mussel Mytilus galloprovincialis is a heat-tolerant species relative to its competative congener M. trossulus, that dominates warm seawater environments but it is unknown how multiple stressors (MS) may affect its physiology. Our study determined the effects of MS on the metabolic rate (MR), superoxide dismutase (SOD) antioxidant enzyme activity, and clearance rate (CR) of M. galloprovincialis. Mussels were exposed for 7 d to hyposalinity (20, 28, 34 ppt) then to heat shock (17, 20, 25 °C) after which MR and SOD activity were determined. CR was quantified following a 30 min MS exposure. We found a significant influence of MS on MR, SOD, and CR. We identified synergistic effects on MR under the most extreme treatment. SOD activity was the greatest under 20 °C exposure while CR declined under heat shock. Thus, our study suggests that mussels experiencing MS may become energy limited as MR increases and feeding rates decrease.

Differentiating metabolomic responses of amphibians to multiple stressors

One of the biggest challenges in ecological risk assessment is determining the impact of multiple stressors on individual organisms and populations in real world scenarios. Frequently, data derived from laboratory studies of single stressors are used to estimate risk parameters and do not adequately address scenarios where other stressors exist. Emerging ‘omic technologies, notably metabolomics, provide an opportunity to address the uncertainties surrounding ecological risk assessment of multiple stressors. The objective of this study was to use metabolomic profiling to investigate the effect of multiple stressors on amphibian metamorphs. We exposed post-metamorphosis (180 days) southern leopard frogs (Lithobates sphenocephala) to the insecticide carbaryl (480 μg/L), predation stress, and a combined pesticide and predation stress treatment. Corticosterone analysis revealed mild support for an induction in response to predation stress alone but strongly suggests that carbaryl exposure, alone or in combination with predation cues, can significantly elevate this known biomarker in amphibians. Metabolomics analysis accurately classed, based on relative nearness, carbaryl and predation induced changes in the hepatic metabolome and biochemical fluxes appear to be associated with a similar biological response. Support vector machine analysis with recursive feature elimination of the acquired metabolomic spectra demonstrated 85–96% classification accuracy among control and all treatment groups when using the top 75 ranked retention time bins. Biochemical fluxes observed in the groups exposed to carbaryl, predation, and the combined treatment include amino acids, sugar derivatives, and purine nucleotides. Ultimately, this methodology could be used to interpret short-term toxicity assays and the presence of environmental stressors to overall metabolomic effects in non-target organisms.

A global synthesis of human impacts on the multifunctionality of streams and rivers.

Human impacts, particularly nutrient pollution and land-use change, have caused significant declines in the quality and quantity of freshwater resources. Most global assessments have concentrated on species diversity and composition, but effects on the multifunctionality of streams and rivers remain unclear. Here, we analyse the most comprehensive compilation of stream ecosystem functions to date to provide an overview of the responses of nutrient uptake, leaf litter decomposition, ecosystem productivity, and food web complexity to six globally pervasive human stressors. We show that human stressors inhibited ecosystem functioning for most stressor-function pairs. Nitrate uptake efficiency was most affected and was inhibited by 347% due to agriculture. However, concomitant negative and positive effects were common even within a given stressor-function pair. Some part of this variability in effect direction could be explained by the structural heterogeneity of the landscape and latitudinal position of the streams. Ranking human stressors by their absolute effects on ecosystem multifunctionality revealed significant effects for all studied stressors, with wastewater effluents (194%), agriculture (148%), and urban land use (137%) having the strongest effects. Our results demonstrate that we are at risk of losing the functional backbone of streams and rivers if human stressors persist in contemporary intensity, and that freshwaters are losing critical ecosystem services that humans rely on. We advocate for more studies on the effects of multiple stressors on ecosystem multifunctionality to improve the functional understanding of human impacts. Finally, freshwater management must shift its focus toward an ecological function-based approach and needs to develop strategies for maintaining or restoring ecosystem functioning of streams and rivers.

How psychosocial stress profile influences the subsequent occurrence of neuropsychiatric comorbidities: A longitudinal population-based cohort study

BackgroundThe role of psychosocial stressors in psychiatric disorders and executive dysfunction has been reported, separately. The literature has also suggested the involvement of social support and coping strategies in these relationships. However, there is a lack of research conducted to examine the relationships among multiple stressors and neuropsychiatric comorbidities while considering the presence of social support and coping strategies. This study aims to articulate the roles of multiple psychosocial stressors, social support, and coping strategies in the subsequent occurrence of neuropsychiatric comorbidities. MethodsData analyzed were from the 6th data collection of a large-scale, longitudinal population-based cohort from Southwest Montreal in Canada. The cumulative effects of multiple stressors were separately examined by a composite score and latent profile analysis. Multinomial logistic regression models were used to test the relationship between cumulative stressors and neuropsychiatric comorbidities. ResultsA total of 210 participants were included in the analyses. The LPA identified a 2-class model for psychosocial stressors (low and high) and executive function (executive dysfunction and no executive dysfunction), respectively. There were 11.8% of participants with neuropsychiatric comorbidities. Both the composite stress score (RR = 1.08, 95%CI = 1.01–1.15) and latent stress groups (RR = 3.65, 95%CI = 1.15–11.57) were associated with neuropsychiatric comorbidities after adjusting for social support and coping strategies. The risk of developing neuropsychiatric comorbidities decreased when the level of social support was high (P < 0.05). ConclusionsExposures to multiple stressors increased the risk of subsequent neuropsychiatric comorbidities, but the risk can be modified by a higher level of social support.

Effects of Harmful Algal Blooms on Fish and Shellfish Species: A Case Study of New Zealand in a Changing Environment.

Harmful algal blooms (HABs) have wide-ranging environmental impacts, including on aquatic species of social and commercial importance. In New Zealand (NZ), strategic growth of the aquaculture industry could be adversely affected by the occurrence of HABs. This review examines HAB species which are known to bloom both globally and in NZ and their effects on commercially important shellfish and fish species. Blooms of Karenia spp. have frequently been associated with mortalities of both fish and shellfish in NZ and the sub-lethal effects of other genera, notably Alexandrium spp., on shellfish (which includes paralysis, a lack of byssus production, and reduced growth) are also of concern. Climate change and anthropogenic impacts may alter HAB population structure and dynamics, as well as the physiological responses of fish and shellfish, potentially further compromising aquatic species. Those HAB species which have been detected in NZ and have the potential to bloom and harm marine life in the future are also discussed. The use of environmental DNA (eDNA) and relevant bioassays are practical tools which enable early detection of novel, problem HAB species and rapid toxin/HAB screening, and new data from HAB monitoring of aquaculture production sites using eDNA are presented. As aquaculture grows to supply a sizable proportion of the world’s protein, the effects of HABs in reducing productivity is of increasing significance. Research into the multiple stressor effects of climate change and HABs on cultured species and using local, recent, HAB strains is needed to accurately assess effects and inform stock management strategies.

Interactions among multiple stressors vary with exposure duration and biological response.

Coastal ecosystems are exposed to multiple anthropogenic stressors. Effective management actions would be better informed from generalized predictions of the individual, combined and interactive effects of multiple stressors; however, few generalities are shared across different meta-analyses. Using an experimental study, we present an approach for analysing regression-based designs with generalized additive models that allowed us to capture nonlinear effects of exposure duration and stressor intensity and access interactions among stressors. We tested the approach on a globally distributed marine diatom, using 72 h photosynthesis and growth assays to quantify the individual and combined effects of three common water quality stressors; photosystem II-inhibiting herbicide exposure, dissolved inorganic nitrogen (DIN) enrichment and reduced light (due to excess suspended sediment). Exposure to DIN and reduced light generally resulted in additivity, while exposure to diuron and reduced light resulted in additive, antagonistic or synergistic interactions, depending on the stressor intensity, exposure period and biological response. We thus find the context of experimental studies to be a primary driver of interactions. The experimental and modelling approaches used here bridge the gap between two-way designs and regression-based studies, which provides a way forward to identify generalities in multiple stressor interactions.

Marine mammal hotspots across the circumpolar Arctic

AbstractAimIdentify hotspots and areas of high species richness for Arctic marine mammals.LocationCircumpolar Arctic.MethodsA total of 2115 biologging devices were deployed on marine mammals from 13 species in the Arctic from 2005 to 2019. Getis‐Ord Gi* hotspots were calculated based on the number of individuals in grid cells for each species and for phylogenetic groups (nine pinnipeds, three cetaceans, all species) and areas with high species richness were identified for summer (Jun‐Nov), winter (Dec‐May) and the entire year. Seasonal habitat differences among species’ hotspots were investigated using Principal Component Analysis.ResultsHotspots and areas with high species richness occurred within the Arctic continental‐shelf seas and within the marginal ice zone, particularly in the “Arctic gateways” of the north Atlantic and Pacific oceans. Summer hotspots were generally found further north than winter hotspots, but there were exceptions to this pattern, including bowhead whales in the Greenland‐Barents Seas and species with coastal distributions in Svalbard, Norway and East Greenland. Areas with high species richness generally overlapped high‐density hotspots. Large regional and seasonal differences in habitat features of hotspots were found among species but also within species from different regions. Gap analysis (discrepancy between hotspots and IUCN ranges) identified species and regions where more research is required.Main conclusionsThis study identified important areas (and habitat types) for Arctic marine mammals using available biotelemetry data. The results herein serve as a benchmark to measure future distributional shifts. Expanded monitoring and telemetry studies are needed on Arctic species to understand the impacts of climate change and concomitant ecosystem changes (synergistic effects of multiple stressors). While efforts should be made to fill knowledge gaps, including regional gaps and more complete sex and age coverage, hotspots identified herein can inform management efforts to mitigate the impacts of human activities and ecological changes, including creation of protected areas.

Multiple stressors: negative effects of nest predation on the viability of a threatened gull in different environmental conditions

The majority of the world's seabirds show substantial population declines, but a detailed understanding of the phenomenon is lacking. A potentially important mechanism that has received momentum lately is nest predation. This study aimed to assess the population viability of a threatened population of the lesser black‐backed gull Larus fuscus fuscus under different scenarios for nest predation and environmental conditions. We merged results from statistical analyses of 16 years of empirical data with a Leslie model, emphasising the impact of predation at the nesting stage. In the model, we quantified the effect of multiple stressors on the viability of the lesser black‐backed gull according to the IUCN Red List's 'Vulnerable' criteria (30% reductions in population size over &lt; 3 generations). First, the empirical analyses showed that the estimated apparent survival probability, which showed declining temporal trends, was on average 0.862 and 0.470 for adults and juveniles, respectively. The average clutch size in the absence and presence of nest predation was 2.836 and 0.935 eggs nest−1, whereas the average number of fledglings nest−1 was 0.452, respectively. Nest predation and chick production showed a concave‐up temporal trend, whereas clutch size showed no trend. Second, based on the predictive models, we documented multiple stressor effects: nest predation was the single‐most‐important stressor, but its adverse effect was severely amplified when environmental conditions were poor. When important nest predators were present, L. f. fuscus met the 'Vulnerable' criteria. Nonetheless, when nest predation was absent or low, the status of our population was following IUCN Red List's 'Least Concern' criteria (its official status). Nest predation played a vital role in limiting population growth – a finding that is likely to be relevant for several other seabirds in northern Europe.