Morphology of the nematocysts of the medusae of two scyphozoans, Catostylus mosaicus and Phyllorhiza punctata (Rhizostomeae): implications for capture of prey

Abstract. We examined the cnidomes (total complement of nematocysts) of medusae of the zooxanthellate and azooxanthellate jellyfishes Phyllorhiza punctata and Catostylus mosaicus (Rhizostomeae, Scyphozoa), and compared the assemblage of zooplankton captured on the oral arms of each species to determine whether differences in the types or amount of zooplankton captured were consistent with possible differences in the cnidomes. Cnidomes were described using light and scanning electron microscopy. Each species had a distinct cnidome and, in general, specimens of P. punctata appeared to have far fewer nematocysts than those of C. mosaicus. Four types of nematocysts were identified in medusae of C. mosaicus; 2 types of holotrichous isorhizae, rhopaloids, and birhopaloids. In C. mosaicus, the oral arms and bell margins possessed all of these types, but the cnidomes of the 2 regions differed in relative abundances and sizes of isorhizae and rhopaloids. Five types of nematocysts were identified in medusae of P. punctata, although not all types were found in all specimens. Round holotrichous isorhizae were found only in the bell, while oval holotrichous isorhizae, rhopaloids of 2 distinct size ranges, and birhopaloids were found in the bell and oral arms. Cnidomes of the bell and oral arms in specimens of P. punctata also differed in the relative abundance and sizes of oval isorhizae and rhopaloids. Although there were clear differences in the overall cnidomes and absolute abundances of nematocysts in each species, the oral arms (feeding appendages) of specimens of both C. mosaicus and P. punctata had similar types and relative abundances of nematocysts. Zooplankton sampled from the oral arms of each species showed that both species preyed predominantly on copepod nauplii and larvae of gastropods and bivalves. Medusae of C. mosaicus captured ～10 × more gastropod larvae and 5 × more bivalve larvae than those of P. punctata. Specimens of P. punctata captured approximately twice as many copepod nauplii as those of C. mosaicus. Differences in the relative abundance of types of zooplankton captured by each species could not be adequately explained by differences in the cnidomes of the oral arms.     

Climate Change,Risks and Contaminants: A Perspective from Studying the Arctic

The Arctic faces threats from climate change and contaminants. Together, these two threats are likely to present surprises centered around the zero-degree isotherm because the phase change of water has enormous potential to affect contaminant transport and transfer, and biological distribution and stress. Particularly at risk are top aquatic predators, migratory species, and species narrowly adapted to ice. These species are most exposed to contaminants, are most likely to become stressed by climate change, or contain within their life cycles efficient vectors of contaminants and diseases. In the Arctic, mercury presents a special case where risks can be altered at many places in the biogeochemical cycle. Atmospheric mercury depletion events offer one such location; however, the methylation of mercury in aquatic systems appears a far more important and presently neglected component of risk from mercury to Arctic ecosystems. Climate variables alter transport, transfer, and capture of contaminants. Therefore, monitoring for contaminants must be conducted with a systems approach that includes climate-related factors. To ensure that the perception of risk is accurate and that priority risks are addressed first, a closer dialogue between scientists, the public, and public administers is urgently required.     

Global Warming: A Consequence of Human Activities Rivaling Earth's Biogeochemical Processes

The planet is growing warmer because of a massive disruption in global biogeochemical cycles. We are burning our reserves of fossil fuels, which formed over a period of 300 million years, in the blink of an eye in geologic time. One manifestation of our addiction to fossil fuels is a dramatic change in the composition of the atmosphere and its radiative properties. Evidence is discussed in this commentary that human-induced global warming has already occurred, that powerful inertia is in place to cause future warming, and that humans and ecosystems are currently being affected. Stabilizing the atmospheric concentration of carbon dioxide at 550 ppm within the next century will require a 70% cutback in emissions. Thus, a whole new system of powering our global economy is necessary.     

Planning Transboundary Ecological Risk Assessments at Military Installations

Ecological risk assessments at military installations that are performed to support natural resources management objectives rely on information from the surrounding region. Stressors such as noise, ozone, and ozone precursors cross installation boundaries, and effects of urbanization and highway development are regional in scale. Ecological populations are not limited to one side of the installation boundary. Therefore, a framework for transboundary ecological risk assessment at military installations is under development. This article summarizes the problem formulation stage. Components include: (1) regional management goals such as installation Integrated Natural Resources Management Plans and land acquisition, (2) involvement of multiple stressors, and (3) large-scale assessment endpoint entities. Challenges of selecting measures of exposure include: quantifying exposure to aggregate stressors, describing land cover consistently in the region, describing rates of land-cover transition, scaling local measurements to a region, and aggregating or isolating exposures from within and outside of the installation. Measures of effect that are important to transboundary or regional ecological risk assessments at military installations are those that represent: effects at a distance from the stressor, large-scale effects, effects of habitat change or fragmentation, spatial extrapolations of localized effects, and integrated effects of multiple stressors. These factors are reflected in conceptual models.     

Assessing Lead Risks at Non-Residential Hazardous Waste Sites

In 1996, the U.S. Environmental Protection Agency (USEPA) developed the Adult Lead Methodology (ALM) to provide an interim approach to assessing risks from non-residential exposures to lead. Because such exposures often involve occupational activities of adults, the ALM was directed at assessing soil-related lead risks to adults. Consistent with other approaches used in Superfund risk assessment, the ALM was designed to predict quasi-steady state blood lead concentrations (PbB) that might result from soil exposure. These predictions are converted to a risk estimate, expressed as the probability of exceeding a PbB level of concern. To examine the assumptions and variables in the ALM that have become available since 1996, a comparison was made of the attributes of seven alternative research models for which adequate documentation is available to understand and implement each approach. Several of these models have been used in regulatory decision-making; however, the USEPA has officially embraced none for general use. This analysis suggests that the ALM can continue to serve as a reasonable tool for assessing risks associated with non-residential exposures to soil. Under certain circumstances other models may be more applicable (i.e., for assessing acute or intensive exposures); however, the ALM is recommended for the majority of risk assessment applications.     

Potential Applications of Population Viability Analysis to Risk Assessment for Invasive Species

Population viability analysis, the use of ecological models to assess a population's risk of extinction, plays an important role in contemporary conservation biology. The premise of this review is that models, concepts, and data analyses that yield results on extinction risk of threatened and endangered species can also tell us about establishment risks of potentially invasive species. I briefly review important results for simple unstructured models, demographic models, and spatial models, giving examples of the application of each type of model to invasive species, and general conclusions about the applicability of each type of model to risk analysis for invasive species. The examples illustrate a portion of the range of potential applications of such models to invasive species, and some of the types of predictions that they can provide. They also highlight some of the limitations of such models. Finally, I present several conjectures and open research questions concerning the application of population viability analyses to risk analysis and control of invasive species.     

A Critical Review of the Traditional Methodology of Cost-Benefit Analysis and a Proposed Alternative

“Risk management” is essential to the decision-making process that prescribes regulations for protecting human health. As a comprehensive decision-making approach, risk management encompasses risk assessment, risk perception, economic factors, and their respective uncertainties. Cost-benefit analysis (CBA) has long been the preferred methodology for evaluating the economic factors associated with such regulations. Within this context, CBA confirms whether or not the “benefit” of a given regulatory option is greater than its “cost.” This article proposes an alternative CBA methodology whose guiding concept is the “optimization” of outcomes for the stakeholders in regulations that aim to protect human health. This article further proposes evaluation criteria for CBA and critiques the traditional and alternative variants against this standard, ultimately to demonstrate the superiority of the latter.     

Underestimation of Risk Due to Exposure Misclassification

Aim. Exposure misclassification constitutes a major obstacle when developing dose-response relationships for risk assessment. A non-differentional error results in underestimation of the risk. If the degree of misclassification is known, adjustment may be achieved by sensitivity analysis. The purpose of this study was to examine the full magnitude of measurement error in determining the prenatal exposure to methylmercury. Materials and methods. We used data from a prospective study of a Faroese birth cohort. Two biomarkers of methylmercury exposure were available, i.e., the mercury concentrations in cord blood and in maternal hair (sampled at the time of parturition). The laboratory imprecision on both chemical analyses was thought to be below 5% (coefficient of variation, CV). As a third exposure parameter, we used the dietary questionnaire response on frequency of whale meat dinners. Factor analysis and structural equation analysis were applied to assess the full extent of the imprecision. Results. The calculated total imprecision much exceeded the known laboratory variation: the CV was 28–30% for the cord-blood concentration and 52–55% for the maternal hair concentration. The dietary questionnaire response was even more imprecise. Conclusions. These findings illustrate that measurement error may be greatly underestimated if judged solely from reproducibility or laboratory quality data. Adjustment by sensitivity analysis is meaningful only if realistic measurement errors are applied. When exposure measurement errors are overlooked or underestimated, decisions based on the precautionary principle will not appropriately reflect the degree of precaution that was intended.     

The Importance of Type II Error and Falsifiability

Aim. Before intergovernmental consensus under the Rio Declaration in 1992, ignorance of type I errors had been disfavoured in science. However, the Precautionary Principle (PP) counsels the avoidance of type II errors, rather than of type I errors. We need a new academic code for the PP. Material and methods. The risk of extinction has usually been evaluated based on conservative estimates of the present population size. I define the weight of evidence as the extinction risk of Japanese vascular plants based on unbiased estimates. Catch quotas in the fisheries are usually decided by precautionary approach. I calculate the long-term yield and risk of stock collapse under a simple stock dynamics model. Results. The weight of evidence depends on the frequency of grids with size unknown. In a few plant species, rankings based on conservative estimates have differed from rankings based on unbiased estimates. In fishery management, a catch quota based on a precautionary approach proved neither sufficient nor necessary to avoid stock collapse. The precautionary approach is one of the reasons that prevent us from maximizing a sustainable yield. Conclusions. We need to clarify the endpoint of risks, and check whether it is necessary to adopt a PP. We can obtain the weight of evidence that is measured under unbiased estimates, while the risk based on a PP is measured under conservative estimates.