Human-induced Stressors Research Articles

Post little ice age drying of eastern Australia conflates understanding of early settlement impacts

Understanding the relative influences of climate and people in driving environmental change is a fundamental aspect of Quaternary research. In Australia, numerous studies have investigated the effect of European settlement on the landscape, yet few have explicitly explored the role that natural climate variability played in modulating those impacts. Using a combination of new and existing proxy data, we demonstrate that European settlement of eastern Australia coincided with a marked decline in available moisture which occurred towards the end of the nineteenth century, c. 1850–1900 CE. This marked decline in rainfall would have increased ecosystem vulnerability to a number of human-induced stressors. By contrast, this aridification is likely to have masked some impacts of European occupation, in particular increased catchment runoff resulting from land clearance. We propose that the eastern Australian landscape has therefore suffered dual stressors of agricultural expansion and climate drying, with implications for both establishing environmental baselines and natural resource management.

Glucocorticoid measurement in plasma, urates, and feathers from California condors (Gymnogyps californianus) in response to a human-induced stressor.

Vertebrates respond to stressful stimuli with the secretion of glucocorticoid (GC) hormones, such as corticosterone (CORT), and measurements of these hormones in wild species can provide insight into physiological responses to environmental and human-induced stressors. California condors (Gymnogyps californianus) are a critically endangered and intensively managed avian species for which information on GC response to stress is lacking. Here we evaluated a commercially available I125 double antibody radioimmunoassay (RIA) and an enzyme-linked immunosorbent assay (ELISA) kit for measurement of CORT and GC metabolites (GCM) in California condor plasma, urate, and feather samples. The precision and accuracy of the RIA assay outperformed the ELISA for CORT and GCM measurements, and CORT and GCM values were not comparable between the two assays for any sample type. RIA measurements of total CORT in condor plasma collected from 41 condors within 15 minutes of a handling stressor were highly variable (median = 70 ng/mL, range = 1–189 ng/mL) and significantly different between wild and captive condors (p = 0.02, two-tailed t-test, n = 10 wild and 11 captive). Urate GCM levels (median = 620 ng/g dry wt., range = 0.74–7200 ng/g dry wt., n = 216) significantly increased within 2 hr of the acute handling stressor (p = 0.032, n = 11 condors, one-tailed paired t-test), while feather section CORT concentrations (median = 18 pg/mm, range = 6.3–68 ng/g, n = 37) also varied widely within and between feathers. Comparison of multiple regression linear models shows condor age as a significant predictors of plasma CORT levels, while age, sex, and plasma CORT levels predicted GCM levels in urates collected within 30 min of the start of handling. Our findings highlight the need for validation when selecting an immunoassay for use with a new species, and suggest that non-invasively collected urates and feathers hold promise for assessing condor responses to acute or chronic environmental and human-induced stressors.

Response of Macrobenthic Invertebrate to Organic Carbon and Particle Size in Lagos Lagoon, Nigeria

Macrobenthic fauna communities are important constituents of soft bottom marine ecosystems which inhabit the bottom environments playing a key factor in controlling structure and functioning of the aquatic environment. Lagos lagoon is the most exposed lagoon to anthropogenic influence in Nigeria coastal lagoon system. Bimonthly sampling was carried out in the Lagos lagoon from September 2014 - July 2016 for water and sediment in twenty – four stations to examine response condition of benthic communities to measures of water quality and sediment quality in Lagos lagoon in order to understand the benthic condition of the aquatic environment. A range of 9 – 91% for sand, 7 – 25% for silt, 0 – 73% for clay while a range of 0 – 4.77 was observed for TOC. The Diversity (H,) richness (d) and evenness (j) were positively correlated with the silt sediment particle size and. Kruskal-Wallis test showed that there was significant difference (p<0.05) between species richness and diversity at all sampling stations. Analysis of variance (ANOVA) showed no significant difference (p>0.05) in mean percentage particle sizes and TOC recorded at the stations but was significant (p<0.05) between TOC and macrobenthic invertebrates. The overall low diversity of macrobenthic fauna observed was attributed to anthropogenic activities majorly industrial dredging and local sand mining which altered the sediment characteristics of the aquatic ecosystem. Assessments of human induced stressors in the lagoon provided information useful for strict regulations and environmental policies to help prevent the aquatic environment from continuous deterioration hence, causing more loss of biodiversity. Responses of macrobenthic invertebrates to measured variables showed that there are high abundance and diversity of ecological groups of sensitive species majorly distributed around the slightly disturbed zones of the study area. In summary, variables examined in this study showed that the total organic content does not have a depleting effect on the abundance of macrobenthic invertebrates because the values are within permissible limits but the particle size characteristics present in this study showed good environmental indicator for evaluating macrobenthic invertebrate responses to stress pattern in water bodies along the coastal areas surrounded by various human activities.

Effects of Bark Beetle Disturbance on Soil Nutrient Retention and Lake Chemistry in Glacial Catchment

Forest ecosystems worldwide are subjected to human-induced stressors, including eutrophication and acidification, and to natural disturbances (for example, insect infestation, windstorms, fires). The occurrence of the later is expected to increase due to the ongoing climate change. These multi-stressor forcings modify ecosystem biogeochemistry, including the retention of limiting nutrients, with implications for terrestrial and aquatic biodiversity. Here we present whole ecosystem nutrient (N, Ca, Mg, K) mass balances in the forested catchment of Plesne Lake, CZ, which has undergone transient changes linked to the recovery from anthropogenic acidification and to the forest disturbances caused by severe infestations by the bark beetle (Ips typographus). Measured fluxes and storage of nutrients in the lake-catchment ecosystem were used to constrain the process-oriented biogeochemical model MAGIC (Model of Acidification of Groundwater In Catchments). Simulated lake water chemistry and changes in soil nutrient pools fitted observed data and revealed that (1) the ecosystem N retention declined, thus nitrate leaching increased for 10 years following the bark beetle disturbance, with transient adverse effects on the acid–base status of lake water, (2) the kinetics of nutrient mineralisation from decaying biomass coupled with nutrient immobilisation in regrowing vegetation constrained the magnitude and duration of ecosystem losses of N, Ca and Mg, (3) the excess of mineralised base cations from decomposing biomass replenished the soil cation exchange matrix, which led to increased soil base saturation, and (4) the improvement of the catchment soil acid–base status led to an increase of lake water pH and acid neutralising capacity. Forested ecosystems underlain by nutrient-poor soils and bedrock are prone to human-induced damages caused by acidification and eutrophication, and any natural disturbance may further lead to nutrient imbalances. We demonstrated that in this natural forest ecosystem protected from human intervention, disturbances together with natural post-disturbance vegetation recovery have temporally positive effects on the nutrient stores in the soil.

Urbanization drives genetic differentiation in physiology and structures the evolution of pace-of-life syndromes in the water flea Daphnia magna.

Natural and human-induced stressors elicit changes in energy metabolism and stress physiology in populations of a wide array of species. Cities are stressful environments that may lead to differential selection on stress-coping mechanisms. Given that city ponds are exposed to the urban heat island effect and receive polluted run-off, organisms inhabiting these ecosystems might show genetic differentiation for physiological traits enabling them to better cope with higher overall stress levels. A common garden study with 62 Daphnia magna genotypes from replicated urban and rural populations revealed that urban Daphnia have significantly higher concentrations of total body fat, proteins and sugars. Baseline activity levels of the antioxidant defence enzymes superoxide dismutase (SOD) and glutathione-S-transferase (GST) were higher in rural compared with city populations, yet urban animals were equally well protected against lipid peroxidation. Our results add to the recent evidence of urbanization-driven changes in stress physiology and energy metabolism in terrestrial organisms. Combining our results with data on urban life history evolution in Daphnia revealed that urban genotypes show a structured pace-of-life syndrome involving both life-history and physiological traits, whereas this is absent in rural populations.

Behavioral differences within and among populations of an African cichlid found in divergent and extreme environments.

Animals are increasingly faced with human-induced stressors that vary in space and time, thus we can expect population-level divergence in behaviors that help animals to cope with environmental change. However, empirical evidence of behavioral trait divergence across environmental extremes is lacking. We tested for variation in behavioral traits among 2 populations of an African cichlid fish (Pseudocrenilabrus multicolor victoriae Seegers, 1990) that experience extremes of dissolved oxygen (DO) and turbidity and are known to vary in a number of physiological and life history traits associated with these stressors. Using a common garden rearing experiment, F1 progeny from wild-caught parents originating from a swamp (low DO, clear) and a river (high DO, turbid) were reared in high DO, clear water. Predator simulation assays were conducted to test for (1) variation in boldness, general activity, and foraging activity between populations, (2) differences in correlations between behaviors within and across populations, and (3) repeatability of behaviors. There was strong evidence for divergence between populations, with swamp fish being more bold (i.e., leaving refuge sooner after a simulated predator attack) and active (i.e., spent more time out of refuge) than river fish. Across populations there were positive correlations between foraging activity and both boldness and general activity; however, within populations, there was only a strong positive relationship between foraging activity and boldness in the river population. Here, we have demonstrated that populations that originate from drastically different environments can produce progeny that exhibit measurable differences in behaviors and their correlated relationships even when reared under common conditions.

Assessment of the Existing Level of Pollution due to Selected Heavy Metals in Surface Sediments of Negombo Lagoon, Sri Lanka

This study was conducted to evaluate the existing level of pollution with respect to selected heavy metals (Fe, Mn, As, Pb, Zn and Cu) in surficial sediments of Negombo Lagoon in Sri Lanka, which is constantly exposed to diverse human induced stresses. Additionally, this study investigated the application of X-ray fluorescence spectroscopy and pollution indices in assessment of heavy metal pollution. A total of 32 surface sediment samples covering the entire lagoon were collected using a grabber sampler and the concentrations of selected heavy metals were analysed using X-ray fluorescence spectroscopy. Furthermore, the concentrations of these heavy metals were used to assess the pollution status of the Negombo Lagoon by an integrated approach using pollution indices such as Enrichment Factor, Geoaccumulation Index and Pollution Load Index. The concentrations of the heavy metals studied were compared with the Canadian sediment quality guidelines which indicate the toxic concentrations of pollutants in sediments that affect aquatic organisms. The mean concentrations of all the heavy metals analysed were higher than the Threshold Effect Level (TEL) while the mean concentration of Arsenic (As) is greater than the Probable Effect Level (PEL) stated in the sediment quality guidelines. The results of Enrichment Factor revealed that the entire Negombo Lagoon is severely enriched by As, while minor enrichment of Copper (Cu) and Zinc (Zn) was observed across the lagoon, suggesting the contribution of anthropogenic sources for metal pollution in surface sediments of the lagoon. Moreover, the calculated Geoaccumulation Indices of the metals studied confirmed that surface sediments of the entire Negombo Lagoon is contaminated with As, Zn and Cu, emphasizing the influence of anthropogenic contamination. However, the concentrations of Manganese (Mn), Iron (Fe) and Lead (Pb) in surface sediments were within their natural range, evidently showing terrigenous origin. The calculated Pollution Load Index revealed that the Negombo Lagoon is considerably polluted by the heavy metals investigated. In conclusion, Arsenic (As) has shown a greater contribution to metal pollution while Zn and Cu were identified as minor enriched contaminants in surface sediments of Negombo Lagoon. The results of this study, while being useful as a reference data base, emphasized the need of effective management strategies for conservation of the lagoon before the pollution level becomes irreversible. Keywords: Heavy metal, Pollution, Coastal contamination, Surface sediments, X-ray fluorescence

In Situ Observations of Foraminiferal Bleaching in the Maldives, Indian Ocean

AbstractCoral reefs are threatened worldwide by a variety of natural and human-induced stressors; anomalous temperatures are presently among the most serious threats by causing extensive coral bleaching. Amphistegina spp. exhibit similar bleaching as corals in the presence of photo-oxidative stress induced by either light or temperature, especially during times of maximum solar irradiance. At 11 islands (34 sampling sites) in the North Ari Atoll in the Maldives, bleaching in Amphistegina was observed a few weeks before the onset of an extensive El Niño-related coral bleaching that was more severe than expected for this region. Assessment using the Amphistegina Bleaching Index (ABI) showed that the proportions of bleached specimens of Amphistegina in April–May 2015 can be explained by photo-inhibitory stress associated with temperatures exceeding 30°C during peak seasonal solar irradiance and water transparency. Importantly, the ABI indicates that environmental conditions are suitable for Amphistegina and other calcifying symbioses at most of the investigated sites, and that either chronic or relatively recent onset of photo-oxidative stress was present at the time of sampling. The observed bleaching in Amphistegina further demonstrates the potential of these unicellular protists to identify stressors in coral reefs; such applications should be considered in future reef-management plans.

Pollution evaluation of total and acid-leachable trace elements in surface sediments of Hooghly River Estuary and Sundarban Mangrove Wetland (India).

The present work investigated the spatial distribution and ecological risk assessment of total and mild acid-leachable trace elements in surface sediments (top 0-10cm; grain size ≤ 63μm) along the Hooghly (Ganges) River Estuary and Sundarban Mangrove Wetland, India. The trace elements, analyzed by ICPMS, showed wide range of variations with the following descending order (mean values expressed in milligrams per kilogram): Fe (25,050 ± 4918) > Al (16,992 ± 4172) > Mn (517 ± 102) > Zn (53 ± 18) > Cu (33 ± 11) > Cr (29 ± 7) > Ni (27 ± 6) > Pb (14 ± 3) > As (5 ± 1) > Se (0.37 ± 0.10) > Cd (0.17 ± 0.13) > Ag (0.16 ± 0.19) > Hg (0.05 ± 0.10). In the acid-leachable fraction, Cd (92%) is dominated followed by Pb (81%), Mn (77%), Cu (70%), and Se (58%) indicating their high mobility, imposing negative impact on the adjacent benthos. The sediment pollution indices (both enrichment factor and contamination factor) suggested severe pollution by Ag at the sampling site Sajnekhali, a wildlife sanctuary in Sundarban. The mean probable effect level quotient indicated that surface sediments in the vicinity of the studied region have 21% probability of toxicity to biota. The result of multivariate analyses affirms lithogenic sources (e.g., weathering parent rocks, dry deposition) for As, Pb, Cr, Cu, and Ni, whereas Cd and Hg originated from anthropogenic activities (such as urban and industrial activities). Both human-induced stresses and natural processes controlled trace element accumulation and distribution in the estuarine system, and remedial measures are required to mitigate the potential impacts of these hazardous trace elements.

Assessing the ecological health of rivers when they are dry

Rivers and streams that dry up are found on every continent, and can form a large proportion of river networks. When rivers are dry, traditional indicators of river health – such as aquatic macroinvertebrates, fish or water quality – cannot be measured. Aquatic health indicators are widely used to assess wetted habitats, but currently no universally applicable indicators have been developed or applied to assess dry riverbed health. Dry riverbeds are often the ‘typical’ state of many intermittent rivers and streams; however, the ecological health of these habitats is rarely, if ever, assessed in monitoring programs. Resource managers have called for indicators of intermittent river health during the dry phase. The use of terrestrial invertebrate biota (e.g. ants, beetles, and spiders) as indicators in this study provides a novel solution to assessing rivers when they are dry.We developed a conceptual model of human-induced stressors (i.e. disturbance by livestock and feral mammals) on dry riverbed biota, which guided the selection of potential health indicators. Livestock and feral mammals are one of the most significant stressors on riverine ecosystems in Queensland, and impact riverbeds by altering the substrate through compaction, rooting and pugging. We trialled the use of metrics of terrestrial invertebrate assemblages as indicators of dry riverbed health in four Australian dryland catchments: Bulloo, Paroo, Warrego and Nebine. We used quantile regression and found that terrestrial invertebrate communities responded negatively (and significantly, p<0.05) to a gradient of disturbance, defined by on-the-ground field measurements of livestock and feral mammal impacts. This response to stressors was predicted by the initial conceptual model.We conclude that terrestrial invertebrates in this study are suitable indicators of dry riverbed health, as they are impacted by disturbance from livestock and feral mammals. They can be used in the same way that indicators, such as aquatic macroinvertebrates, are traditionally used to assess river health. We also successfully combined indicators of wet and dry habitats to provide a holistic assessment of the health of intermittent river ecosystems incorporating all sections of the river network. We suggest that this approach should be adopted by other river health monitoring programs in rivers around the world.

Synergy effects of fluoxetine and variability in temperature lead to proportionally greater fitness costs in Daphnia: A multigenerational test

Increased variability in water temperature is predicted to impose disproportionally greater fitness costs than mean increase in temperature. Additionally, water contaminants are currently a major source of human-induced stress likely to produce fitness costs. Global change models forecast an increase in these two human-induced stressors. Yet, in spite the growing interest in understanding how organisms respond to global change, the joint fitness effects of water pollution and increased variability in temperature remain unclear. Here, using a multigenerational design, we test the hypothesis that exposure to high concentrations of fluoxetine, a human medicine commonly found in freshwater systems, causes increased lifetime fitness costs, when associated with increased variability in temperature. Although fluoxetine and variability in temperature elicited some fitness cost when tested alone, when both stressors acted together the costs were disproportionally greater. The combined effect of fluoxetine and variability in temperature led to a reduction of 37% in lifetime reproductive success and a 17.9% decrease in population growth rate. Interestingly, fluoxetine and variability in temperature had no effect on the probability of survival. Freshwater systems are among the most imperilled ecosystems, often exposed to multiple human-induced stressors. Our results indicate that organisms face greater fitness risk when exposed to multiple stressors at the same time than when each stress acts alone. Our study highlights the importance of using a multi-generational approach to fully understand individual environmental tolerance and its responses to a global change scenario in aquatic systems.

Improving the performance of the EPT Index to accommodate multiple stressors in Afrotropical streams

The EPT index (Ephemeroptera, Plecoptera and Trichoptera) may be skewed by the wide tolerance to multiple stressors of the Baetid, Caenid and Hydropsychid families, which affects the performance of the EPT index as an indicator of multiple stressors in aquatic ecosystems. The effect of the BCH families on the EPT index was evaluated and alternatives were considered to improve its performance. The hypothesis that the removal of the BCH families improves sensitivity of the EPT index to human-induced stressors in streams and rivers was tested. Macroinvertebrates were collected in January–March 2009 at 22 sites in the Nyando and Nzoia Rivers, Lake Victoria basin, Kenya. Nine derivatives and modifications of the EPT index were tested for responses to a disturbance gradient, ranked into three condition categories (reference, intermediate and impaired). The sensitivity of the proportionate abundance derivative of the EPT index improved when the BCH families were removed, whereas that of the richness derivative improved marginally. Other modifications considered performed poorly when compared with the EPT-BCH metrics. Wide distribution of the BCH across all sites, irrespective of the level of disturbance, reduced the sensitivity of the EPT index in the studied streams. The removal of the BCH families enhanced the sensitivity of the index to multiple stressors in Afrotropical streams and rivers.

Human activities as a driver of spatial variation in the trophic structure of fish communities on Pacific coral reefs.

Anthropogenic activities such as land-use change, pollution and fishing impact the trophic structure of coral reef fishes, which can influence ecosystem health and function. Although these impacts may be ubiquitous, they are not consistent across the tropical Pacific Ocean. Using an extensive database of fish biomass sampled using underwater visual transects on coral reefs, we modelled the impact of human activities on food webs at Pacific-wide and regional (1,000s-10,000skm) scales. We found significantly lower biomass of sharks and carnivores, where there were higher densities of human populations (hereafter referred to as human activity); however, these patterns were not spatially consistent as there were significant differences in the trophic structures of fishes among biogeographic regions. Additionally, we found significant changes in the benthic structure of reef environments, notably a decline in coral cover where there was more human activity. Direct human impacts were the strongest in the upper part of the food web, where we found that in a majority of the Pacific, the biomass of reef sharks and carnivores were significantly and negatively associated with human activity. Finally, although human-induced stressors varied in strength and significance throughout the coral reef food web across the Pacific, socioeconomic variables explained more variation in reef fish trophic structure than habitat variables in a majority of the biogeographic regions. Notably, economic development (measured as GDP per capita) did not guarantee healthy reef ecosystems (high coral cover and greater fish biomass). Our results indicate that human activities are significantly shaping patterns of trophic structure of reef fishes in a spatially nonuniform manner across the Pacific Ocean, by altering processes that organize communities in both "top-down" (fishing of predators) and "bottom-up" (degradation of benthic communities) contexts.

The effects of small-scale coastal development on the eelgrass (Zostera marina L.) distribution along the Swedish west coast – Ecological impact and legal challenges

Anthropogenic impacts on coastal areas have led to an increased degradation of marine environments globally. Eelgrass ecosystems are particularly susceptible to human induced stressors as they are sensitive to low light conditions and usually grow in shallow protected areas where pressure from coastal development is high. The extensive decline in coverage of eelgrass along the Swedish Northwest coast since the 1980s has largely been attributed to the effects of coastal eutrophication and overfishing. However, the impact on eelgrass from small-scale coastal development (docks and marinas) has never been investigated in this area. The aim of this study was to assess the local and large-scale effect of shading by docks and marinas on eelgrass habitats along the Swedish NW coast and to investigate the decision process behind small-scale exploitation to identify problems with the current legislation, which allows for continued exploitation of eelgrass. Through field assessments of eelgrass around docks and analysis of available data on eelgrass and dock distribution along the coast, the present study demonstrates that shading from docks reduced eelgrass coverage with on average 42–64% under and adjacent to the docks, and that floating docks affected larger areas and caused a much stronger reduction in eelgrass coverage (up to 100% loss) compared to docks elevated on poles (up to 70% reduction in coverage). The total eelgrass area negatively affected by docks and marinas along the NW coast was estimated to approximately 480 ha, an area corresponding to over 7% of the present areal coverage of eelgrass in the region. The analysis of decisions for dock construction showed that eelgrass was generally not assessed or considered in the decision process and that 69–88% of the applications were approved also in areas where eelgrass was present. Furthermore, marine protected areas only marginally reduced the approval of applications in eelgrass habitats. The continued small-scale development along the Swedish NW coast constitutes a significant threat to the already decimated coverage of eelgrass along the coast and changes in the management practices are needed in order to achieve both national and international goals on environmental status.

Designing spatially cohesive nature reserves with backup coverage

ABSTRACTNatural habitats continue to dwindle due to a variety of natural and human-induced stressors. In response, sufficient land must be set aside for conservation to preserve long-term biodiversity. In this paper, we propose a bi-objective optimization model to form spatially cohesive nature reserves by minimizing the distance from habitat patches to the center of their reserve, while simultaneously maximizing the ecological condition of the patches set aside for preservation. Our model can accommodate multiple reserves which, combined with a minimum separation distance requirement, enforces backup coverage to mitigate the possible effects of natural and anthropogenic stressors. The model fully capitalizes on GIS functionalities to extract information on spatial relationships and visualize optimization results. Given the complexity of the separation constraint, we propose a genetic algorithm (GA) and a two-phase heuristic where the GA solves the selection of the reserves, while a solver attempts to optimize the allocation of patches to the selected reserves. The behavior of our model and its sensitivity to the parameters are illustrated on a simulated data set, while its real-world problem-solving capabilities are demonstrated on a case study in New Hampshire. Our model provides an alternative modeling tool for conservation planning, particularly when backup reserves are desired.

Biomass Equations and Assessment of Carbon Stock of &lt;i&gt;Calligonum polygonoides&lt;/i&gt; L., a Shrub of Indian Arid Zone

Biomass equations of Calligonum polygonoides L. were derived for the arid districts of Rajasthan, India for assessment of carbon stock. Plants varied spatially in growth and biomass (0.03-54.19 kg/plant). Contribution of stems and roots was 45.7% and 48.0% of total biomass respectively. Nonlinear models were found to be the best in predicting biomass of stems, roots, above-ground and total biomass of C. polygonoides using collar diameter as the predictor. Carbon concentration was highest in twigs followed by stems, roots and leaves. Carbon density due to this species ranged between 0.37 and 1.84 t/ha. Conclusively, collar diameter alone is sufficient to predict the biomass of different components of this plant. Varying climatic and human-induced stresses were found to affect the biomass and carbon sequestration by this species.

Moderate ocean warming mitigates, but more extreme warming exacerbates the impacts of zinc from engineered nanoparticles on a marine larva

There is growing concern about the combined effects of multiple human-induced stressors on biodiversity. In particular, there are substantial knowledge gaps about the combined effects of existing stressors (e.g. pollution) and predicted environmental stress from climate change (e.g. ocean warming). We investigated the impacts of ocean warming and engineered nanoparticles (nano-zinc oxide, nZnO) on larvae of a cosmopolitan tropical sea urchin, Tripneustes gratilla. Larval T. gratilla were exposed to all combinations of three temperatures, 25, 27 and 29 °C (current SST and near-future predicted warming of +2 and + 4 °C) and six concentrations of nZnO (0, 0.001, 0.01, 0.1, 1 and 10 mg nZnO·L−1). These stressors had strong interactive effects on fertilization, gastrulation and normal development of 5 day old larvae. High concentrations of nZnO had a negative effect, but this impact was less pronounced for sea urchins reared at their preferred temperature of 27 °C compared to 25 or 29 °C. Larval growth was also impacted by combined stress of elevated temperature and nZnO. Subsequent measurement of the dissolution and aggregation of nZnO particles and the direct effect of Zn2+ ions on larvae, suggest the negative effects of nZnO on larval development and growth were most likely due to Zn2+ ions. Our results demonstrate that marine larvae may be more resilient to stressors at optimal temperatures and highlight the potential for ocean warming to exacerbate the effects of pollution on marine larvae.

Additive effects prevail: The response of biota to multiple stressors in an intensively monitored watershed

Freshwater ecosystems are impacted by a range of stressors arising from diverse human-caused land and water uses. Identifying the relative importance of single stressors and understanding how multiple stressors interact and jointly affect biology is crucial for River Basin Management.This study addressed multiple human-induced stressors and their effects on the aquatic flora and fauna based on data from standard WFD monitoring schemes. For altogether 1095 sites within a mountainous catchment, we used 12 stressor variables covering three different stressor groups: riparian land use, physical habitat quality and nutrient enrichment. Twenty-one biological metrics calculated from taxa lists of three organism groups (fish, benthic invertebrates and aquatic macrophytes) served as response variables. Stressor and response variables were subjected to Boosted Regression Tree (BRT) analysis to identify stressor hierarchy and stressor interactions and subsequently to Generalised Linear Regression Modelling (GLM) to quantify the stressors standardised effect size.Our results show that riverine habitat degradation was the dominant stressor group for the river fauna, notably the bed physical habitat structure. Overall, the explained variation in benthic invertebrate metrics was higher than it was in fish and macrophyte metrics. In particular, general integrative (aggregate) metrics such as % Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa performed better than ecological traits (e.g. % feeding types). Overall, additive stressor effects dominated, while significant and meaningful stressor interactions were generally rare and weak.We concluded that given the type of stressor and ecological response variables addressed in this study, river basin managers do not need to bother much about complex stressor interactions, but can focus on the prevailing stressors according to the hierarchy identified.

Forest structure and soil properties of mangrove ecosystems under different management scenarios: Experiences from the intensely humanized landscape of Indian Sunderbans

The mangrove stands in and around the densely populated rural areas of Indian Sunderbans are experiencing intense human induced stresses in the forms of widespread small-scale logging, shrimp monoculture, riverside prawn-seed and crab catching, forest trespassing, oil-spill etc. Here, restoration of degraded sites and management of remaining mangroves often remain unsuccessful in serving the dual purposes of biodiversity conservation and sustainable livelihood generation. In this context, the present study aims to evaluate the effects of different management scenarios on vegetation structure and composition as well as soil physico-chemical properties along salinity gradients of two mangrove sites located at village-fringe areas of Sunderbans. Transect cum quadrant-based analyses of vegetation and soil samples were adopted for this purpose in consultation with local community members. The results showed that the mangrove site jointly managed by a non-governmental organization and local forest dependents was performing noticeably better than the other site under surveillance of the State Forest Department. Most of the vegetation (basal area, species diversity index, tree density) and few of the soil (pH, cation exchange capacity, exchangeable Na%, soil total C, and organic C stocks) parameters were in significantly superior conditions in the first site than the later in terms of ecological health (p < 0.01). Soil salinity exhibited significantly negative correlations with the vegetation characteristics of both sites from riverbank towards inland. While the first site represented the growth of a multi-layered canopy with mixed species association, the later site was characterized by mono-specific dominance of the Avicennia varieties primarily due to indiscriminate exploitative activities. Thus, passive restoration or self-recovery of mangroves was considered inadequate in these circumstances for regaining natural ecological functionality. Alternatively, an active human intervention engaging the local forest dependents in decision-making and implementation initiatives regarding recognition of actual causes of degradation, zone-wise selection of species, fixation of gestation period, protection, and equitable usufruct sharing was recommended as the prerequisite towards successful restoration of these fragile mangrove ecosystems.

At what scale and extent environmental gradients and climatic changes influence stream invertebrate communities?

In a context of increasing landscape modifications and climatic changes, scale hierarchy becomes an ever more crucial issue to integrate in the analysis of drivers and stressors of biological communities, especially in river networks. To cope with this issue, we developed (i) spatial hierarchical models of functional diversity of stream invertebrate communities to assess the relative influence of local- vs. regional-scale factors in structuring community assembly, and (ii) analysis of metacommunity elements to determine the ecological processes behind the structuring. The spatial structuring of benthic invertebrate communities was investigated over 568 sites in South-eastern France. Community structure was mainly driven by the altitudinal gradient and spring flow variation at broad scales, with functional diversity gradually decreasing with elevation and being maximized at intermediate levels of flow variability. According to the 'elements of metacommunity structure' analysis, the prevailing influence of the altitudinal gradient was also supported by a Clementsian structuration of invertebrate communities. Conversely, the influence of observed climatic changes in temperature and rainfall was weak and observed only at fine scales. As a result, natural environmental filters were stronger drivers of the functional diversity of communities than human-induced stressors (e.g. water pollution and hydromorphological alterations). More broadly, our results suggest that management needs to embrace the possibilities of gathering high spatial and taxonomical resolution data when analysing and predicting flow variation and climate change effects in order to preserve and restore functionally diverse communities. Moreover, to develop environmental flow schemes or restoration and climate change adaptation strategies for freshwater communities, local and regional processes need to be addressed simultaneously; equally responsible as drivers of community diversity.