Recovery of copepod, but not cladoceran, zooplankton from severe and chronic effects of multiple stressors

In the mid‐twentieth century, many lakes near Sudbury, Canada, were severely contaminated by acid and metal emissions from local smelters. For example, in the early 1970s, Middle Lake had pH of 4.2, and Cu and Ni levels both >0.5 mg L^?1 . To determine if crustacean zooplankton could recover from such severe and chronic damage, Middle Lake was neutralized in 1973. A comparison of its zooplankton with that of 22 reference (pH > 6) lakes indicates that the planktonic Copepoda completely recovered by 2001. In contrast, the cladoceran assemblage improved but did not recover. Colonist sources existed – Cladocera and Copepoda occurred with equal frequency in area lakes – but six separate colonizations by cladoceran species failed. We argue that local factors, metal toxicity and predation by yellow perch, have, to date, prevented cladoceran recovery. Nonetheless, the complete copepod recovery is encouraging, given the severity and duration of pre‐neutralization stress.     

Cumulative Health Risk Assessment: Finding New Ideas and Escaping from the Old Ones

Cumulative risk assessment (CRA) is an emergent tool for organizing and analyzing scientific information to examine, characterize, and possibly quantify adverse health outcomes from combined effects of exposure to diverse environmental factors, including both chemical and nonchemical stressors. This article examines the implementation of effects-based CRA, which emphasizes evaluating health risks in a defined community or population, as opposed to stressor-based approaches, which focus on determining health risks for a defined set of stressors. It discusses the concept of vulnerability-based CRA as a potentially useful alternative, reviews the conceptual constructs that underpin CRA, surveys the diversity of methods available for putting effects-based principles into practice, identifies impediments hindering practical applications, and examines ways to make effects-based CRA more feasible.     

Forecasting the combined effects of anticipated climate change and agricultural conservation practices on fish recruitment dynamics in Lake Erie

1. Many aquatic ecosystems are experiencing multiple anthropogenic stressors that threaten their ability to support ecologically and economically important fish species. Two of the most ubiquitous stressors are climate change and non-point source nutrient pollution.
2. Agricultural conservation practices (ACPs, i.e. farming practices that reduce runoff, prevent erosion, and curb excessive nutrient loading) offer a potential means to mitigate the negative effects of non-point source pollution on fish populations. However, our understanding of how ACP implementation amidst a changing climate will affect fish production in large ecosystems that receive substantial upstream sediment and nutrient inputs remains incomplete.
3. Towards this end, we explored how anticipated climate change and the implementation of realistic ACPs might alter the recruitment dynamics of three fish populations (native walleye Sander vitreus and yellow perch Perca flavescens and invasive white perch Morone americana) in the highly productive, dynamic west basin of Lake Erie. We projected future (2020–2065) recruitment under different combinations of anticipated climate change (n = 2 levels) and ACP implementation (n = 4 levels) in the western Lake Erie catchment using predictive biological models driven by forecasted winter severity, spring warming rate, and Maumee River total phosphorus loads that were generated from linked climate, catchment-hydrology, and agricultural-practice-simulation models.
4. In general, our models projected reduced walleye and yellow perch recruitment whereas invasive white perch recruitment was projected to remain stable or increase relative to the recent past. Our modelling also suggests the potential for trade-offs, as ACP implementation was projected to reduce yellow perch recruitment with anticipated climate change.
5. Overall, our study presents a useful modelling framework to forecast fish recruitment in Lake Erie and elsewhere, as well as offering projections and new avenues of research that could help resource management agencies and policy-makers develop adaptive and resilient management strategies in the face of anticipated climate and land-management change.

     

A Procedure for Ecological Tiered Assessment of Risks (PETAR)

Several procedures for Ecological Risk Assessment (ERA) have been suggested. The use of these existing procedures often relies on availability of existing data and/or on large resources for acquisition of new ones. This paper presents a three-tiered procedure for retrospective evaluation of risks adapted to limited resources and scarce background information of relevance for risk assessments, such as in developing countries. The tiers require successively more detailed investigations. The approach assures that resources available for site-specific investigations are directed towards well-formulated questions raised during previous stages of the assessment. The first tier, the preliminary assessment, is a qualitative evaluation of existing information on anthropogenic stressors, sources of stressors and expected ecological effects. The second tier is a regional risk assessment; a semi-quantitative evaluation of ecological risks, over large geographical areas, which results in a ranking of sources and stressors having the greatest potential for ecological impact and ranking of subareas inside the study area more likely to be impacted. The final tier is a site-specific and quantitative risk assessment, at a smaller scale and requiring more resources, that incorporates methodologies for establishing causality between exposure to multiple stressors and effects on specific endpoints of ecological and societal relevance.     

Dietary restriction and longevity extension as a manifestation of Hormesis

Restricting the food intake of rats and mice to 60% of ad libitum intake has been shown to significantly slow their aging processes and markedly extend length of life. Evidence is presented that indicates the antiaging action of this dietary restriction is a manifestation of hormesis and acts by enabling the animal to cope with stressors, including the low‐intensity, long‐term intrinsic and extrinsic stressors conjectured to cause aging. A hypothesis is offered for the evolutionarily adaptive basis of the antiaging action of dietary restriction: It proposes that this antiaging action is a byproduct of the evolution of mechanisms that enabled animals living in the wild to survive unpredictable and relatively brief periods of food scarcity. Likely proximate mechanisms of antiaging action of dietary restriction are considered. Enhancement of the stress response genes, particularly the heat shock protein genes, appears to be importantly involved. Evidence indicates that moderate hyperadrenocorticism also plays a significant role. These proximate mechanisms may well be major players in other examples of hormesis.     

Climate-induced changes in bottom-up and top-down processes independently alter a marine ecosystem

Climate change has complex structural impacts on coastal ecosystems. Global warming is linked to a widespread decline in body size, whereas increased flood frequency can amplify nutrient enrichment through enhanced run-off. Altered population body-size structure represents a disruption in top-down control, whereas eutrophication embodies a change in bottom-up forcing. These processes are typically studied in isolation and little is known about their potential interactive effects. Here, we present the results of an in situ experiment examining the combined effects of top-down and bottom-up forces on the structure of a coastal marine community. Reduced average body mass of the top predator (the shore crab, Carcinus maenas) and nutrient enrichment combined additively to alter mean community body mass. Nutrient enrichment increased species richness and overall density of organisms. Reduced top-predator body mass increased community biomass. Additionally, we found evidence for an allometrically induced trophic cascade. Here, the reduction in top-predator body mass enabled greater biomass of intermediate fish predators within the mesocosms. This, in turn, suppressed key micrograzers, which led to an overall increase in microalgal biomass. This response highlights the possibility for climate-induced trophic cascades, driven by altered size structure of populations, rather than species extinction.     

The effects of toxicants on planktonic systems: an integrated approach using the analysis of size distributions

We measured size distributions in model wetlands to detect stressor effects at the community level. Two experiments investigated the individual and combined effects of methyl mercury, chlorpyrifos, atrazine, monosodium methane arsonate, and UV-B light on the system. The statistical analysis of the metric using size distributions, which integrated information about organisms 0.2–4750 µm in size, detected effects in the planktonic community. Effects were found in both experiments, but only when methyl mercury was present in the treatment structure, indicating that system level effects are most likely with broad spectrum or persistent toxicants. Methyl mercury negatively affected most size classes measured in both experiments. A methyl mercury × chlorpyrifos interaction was detected which shifted the size distribution to larger organisms more than expected, but the interaction effect was much smaller than the effect of methyl mercury alone.