Interactions between morphological and physiological plasticity optimize energy acquisition in corals

Morphological plasticity in response to environmental heterogeneity may be performance enhancing or may simply result from an intrinsic instability in morphology during development. Although patterns of morphological change are well documented for numerous taxa, it is often unclear whether this plasticity enhances the performance of organisms in the habitat to which they have acclimatized. Reef-building corals are an ideal model system in which to investigate this question. We here develop a three-dimensional geometric model and present a comprehensive photosynthesis data set with experimentally calibrated photosynthesis models that predicts energy acquisition by foliose corals as a function of colony shape. This allows us to assess the extent to which changes in colony morphology along an environmental gradient track the predicted optimal colony morphologies. Our results provide strong evidence that phenotypic plasticity in foliose corals optimizes photosynthetic energy acquisition and is not simply a mechanism to increase light capture. We show that the optimal morphology is constrained at the boundaries of the environmental gradient, with non-optimal morphologies in these habitats having greatly reduced energy acquisition. However, at the center of the environmental gradient, flexibility in photophysiology allows energy acquisition to be very similar for multiple morphologies. Our results highlight the importance of phenotypic plasticity at multiple scales. Variation in overall morphology is important at niche boundaries at which conditions are consistently more stressful, whereas physiological flexibility is important in intermediate and less predictable habitats in which a rapid and reversible response to environmental fluctuations is required.     

Temperature as a key driver of ecological sorting among invasive pest species in the tropical Andes

Invasive species are a major threat to the sustainable provision of ecosystem products and services, both in natural and agricultural ecosystems. To understand the spatial arrangement of species successively introduced into the same ecosystem, we examined the tolerance to temperature and analyzed the field distribution of three potato tuber moths (PTM, Lepidoptera: Gelechiidae), that were introduced in Ecuador since the 1980s. We studied physiological responses to constant temperatures of the three PTM species under laboratory conditions and modeled consequences for their overall population dynamics. We then compared our predictions to field abundances of PTM adults collected in 42 sites throughout central Ecuador. Results showed that the three PTM species differed with respect to their physiological response to temperature. Symmetrischema tangolias was more cold tolerant while Tecia solanivora had the highest growth rates at warmer temperatures. Phthorimaea operculella showed the poorest physiological performance across the range of tested temperatures. Overall, field distributions agree with predictions based on physiological experiments and life table analyses. At elevations >3000 m, the most cold-tolerant species, S. tangolias, was typically dominant and often the only species present. This species may therefore represent a biological sensor of climate change. At low elevations (<2700 m), T. solanivora was generally the most abundant species, probably due to its high fecundity at high temperatures. At mid elevations, the three species co-occurred, but P. operculella was generally the least abundant species. Consistent with these qualitative results, significant regression analyses found that the best predictors of field abundance were temperature and a species x temperature interaction term. Our results suggest that the climatic diversity in agricultural landscapes can directly affect the community composition following sequential invasions. In the tropical Andes, as in other mountain ecosystems, the wide range of thermal environments found along elevational gradients may be one reason why the risks of invasion by successively introduced pest species could increase in the near future. More data on potential biological risks associated with climatic warming trends in mountain systems are therefore urgently needed, especially in developing nations where such studies are lacking.     

Using stable isotopes to monitor anthropogenic nitrogen inputs to estuaries

Use of stable nitrogen isotope ratios is one method that has been proposed to indicate anthropogenic nutrient enrichment in estuarine systems. However, the role of stable isotopes as a tool in long-term ecosystem monitoring has not been fully developed. Resident producer and consumer species were collected from marshes dominated by Spartina alterniflora and subject to a range of anthropogenic impacts in Cape Cod, Massachusetts, and in Great South Bay and Jamaica Bay, New York. Tissue isotope ratios of Spartina alterniflora, Ulva lactuca, Fundulus heteroclitus, and Geukensia demissa were analyzed in order to determine which organisms are the most sensitive indicators of changes in anthropogenic nitrogen source and loading. Power analysis was used to determine the sample sizes necessary to detect change in nutrient source using the species sampled. Relationships between the delta15N values of the species sampled and watershed population density and residential development were evaluated. Population density was a better indicator of anthropogenic nitrogen impact than residential development, since most anthropogenic nitrogen in the study marshes was derived from wastewater. Consumer species demonstrated lower within-site variability than producer species and would therefore require smaller sample sizes to detect changes in nitrogen source and loading.     

The Role of Biological Indicators in a State Water Quality Management Process

State water quality agencies are custodians of water quality management programs under the Clean Water Act of which the protection and restoration of biological integrity in surface waters is an integral goal. However, an inappropriate reliance on chemical/physical stressor and exposure data or administrative indicators in place of the direct measurement of ecological response has led to an incomplete foundation for water resource management. As point sources have declined in significance, the consequences of this flawed foundation for dealing with the major limitations to biological integrity (nonpoint sources, habitat degradation) have become more apparent. The use of biocriteria in Ohio, for example, resulted in the identification of 50% more impairment than a water chemistry approach alone and other inconsistencies of a flawed monitoring foundation are illustrated in the national 305(b) report statistics on waters monitored, aquatic life use attainment, and habitat degradation. Biological criteria (biocriteria) incorporates the broader concept of water resource integrity to supplement the roles of chemical and toxicological approaches and reduces the likelihood of making overly optimistic estimates of aquatic life condition. A carefully conceived ambient monitoring approach comprised of biological, chemical, and physical measures ensures all relevant stressors to water resource integrity are identified and that the efficacy of administrative actions can be directly measured with environmental results. New multimetric indices, such as the IBI, ICI, and BIBI represent a significant advancement in aquatic resource characterization that have allowed the inclusion of biological information into many States water quality management programs. Ohio adopted numerical biocriteria in the Ohio water quality standards regulations in May 1990 and, through multiple aquatic life uses that reflect a continuum of biological condition, represents a tiered approach to water resource management. Biocriteria provide the impetus and opportunity to recognize and account for natural, ecological variability in the environment, something which previously was been lacking in state water quality management programs. The upper Great Miami River in Ohio illustrates a case study where bioassessment data documented the efficacy of efforts to permit, fund, and construct municipal treatment systems in restoring aquatic life. In contrast, in the Mahoning River similar administrative actions were inadequate to restore aquatic life in an environment with severe sediment contamination and impacts from combined sewer overflows. A biocriteria-based goal of restoring 75% of aquatic life uses by the year 2000 in Ohio has led to the use of biological data to identify trends and forecast the status and the causes and sources of impairment to Ohio streams, an effort that should affect the strategic focus of our water resource management efforts. A biocriteria-based approach has profoundly influenced strategic planning and priority setting, water quality based permitting, water quality standards, basic monitoring and reporting, nonpoint source assessment, and problem discovery within Ohio EPA.     

Dust explosions: How should the influence of humidity be taken into account?

In this work, the influence of humidity on dust explosions of metallic (aluminium) and organic materials (icing sugar, polyethylene and magnesium stearate) has been studied. The impact of pre-humidification of powders on their ignition sensitivity, their volume resistivity and charge decay time has been assessed. The influence of humidity on explosion severity has also been studied by two methods: on the one hand, the dust sample was stored in a controlled workstation at constant relative humidity; on the other hand, the dry dust was dispersed in a humidity controlled atmosphere in the vessel.As expected, the effect of humidity strongly depends on the chemical nature of the particles. Experiments on powders volume resistivity and charge decay time have shown typical trends but have especially pointed out the inadequacy of some standards. Inhibition phenomena have been verified for polyethylene and magnesium stearate, whereas both inhibition and promotion have been observed for icing sugar and could be explained by an evolution of sucrose structure. Dry aluminium dust explosions in humid atmosphere show that water vapour inerts the explosion. However, when aluminium is stored at controlled humidity, the maximum rise of pressure rate increases with the water content, which is probably due to hydrogen generation.     

Environmental hazards and waste management in Nsukka urban metropolis in Enugu State of Nigeria: how much are people willing to pay?

Solid waste management in Nsukka town in Enugu state of Nigeria has remained a major challenge despite the efforts of the state government through the Enugu State Waste Management Agency (ESWAMA). The current method whereby households dump refuse at designated locations by the road side to be cleared later has not yielded much improved sanitation of the town. In this study we propose an alternative waste management method that is believed to be superior to the status quo if properly managed. This study applies Contingent Valuation Method (CVM) to estimate the households’ willingness to pay (WTP) for this new method in order to ascertain its applicability in Nsukka urban. Data were collected from a sample of 500 households stratified according to major streets in the town. The results show that the mean WTP using different specifications of the model varies from N527.50 (about 2.68) to N530.90 (about 2.68) per month. The policy implication is that if the waste management agency adopts the proposed scenario and manages it well the average revenue realizable per month would be about N13,750,516 (about $69,800). The authorities can compare this with the cost of providing the service and see if it is worth the effort.     

Hurricane Katrina‐linked environmental injustice: race,class, and place differentials in attitudes

Claims of environmental injustice, human neglect, and racism dominated the popular and academic literature after Hurricane Katrina struck the United States in August 2005. A systematic analysis of environmental injustice from the perspective of the survivors remains scanty or nonexistent. This paper presents, therefore, a systematic empirical analysis of the key determinants of Katrina‐induced environmental injustice attitudes among survivors in severely affected parishes (counties) in Louisiana and Mississippi three years into the recovery process. Statistical models based on a random sample of survivors were estimated, with the results revealing significant predictors such as age, children in household under 18, education, homeownership, and race. The results further indicate that African‐Americans were more likely to perceive environmental injustice following Katrina than their white counterparts. Indeed, the investigation reveals that there are substantial racial gaps in measures of environmental injustice. The theoretical, methodological, and applied policy implications of these findings are discussed.     

Geographic variation in polyphenolic levels of Northeastern Pacific kelps and rockweeds

Brown algal polyphenolic compounds are secondary metabolites whose functions may include protecting plants from pathogens or damage by UV radiation, and deterring feeding by herbivores. We present here the first analysis of spatial variation (at scales from tens of meters to hundreds of kilometers) in concentration of these compounds in two orders of brown algae from the northeastern Pacific Ocean. In kelps (order Laminariales), variation among sites was significant in only 25% of species examined and was consistent within families (high in the Alariaceae and low in the Laminariaceae and Lessoniaceae). In rockweeds (order Fucales, family Fucaceae), site variation was high in three of four species examined. Both the proportion of high polyphenolic kelp species and the magnitude of spatial variation within species from both kelps and rockweeds were much higher than would have been predicted from previous studies in other regions. In one kelp (Laminaria groenlandica), significant differences between sites occurred at scales of only tens of meters. No latitudinal clines were observed. Differences in phenolic concentrations of kelps spanned nearly an order of magnitude in one species, Hedophyllum sessile. Phenolic levels were significantly higher in members of the Fucales than the Laminariales, but showed no significant differences between intertidal and subtidal species. Received: 22 July 1996 / Accepted: 26 October 1998     

Marginal tentacles of the corallimorpharian Rhodactis rhodostoma. 1. Role in competition for space

The corallimorpharian Rhodactis rhodostoma (Ehrenberg, 1934) forms aggregations that dominate patches on some coral reef flats in the Red Sea. The outcomes and mechanisms of competition for space between this corallimorpharian and other sessile organisms are poorly understood. Polyps of R. rhodostoma were observed to overgrow zoanthids, hydrozoan corals, sponges and encrusting macroalgae on a fringing reef at Eilat, northern Red Sea. R. rhodostoma polyps also damaged, and in some cases overgrew, reef-building corals in the families Poritidae, Acroporidae and Pocilloporidae, most of which form branching colonies with small polyps that are subordinate in coral competitive hierarchies. In contrast, most stony corals in the families Faviidae and Mussidae had standoff interactions with R. rhodostoma, in which they prevented the corallimorpharians from damaging them or approaching closer than 1 to 3 cm. The latter corals are ranked at the top of competitive hierarchies for Indo-Pacific corals, and they form massive colonies of large polyps which may develop aggressive organs termed sweeper tentacles. Some soft corals that exude allelopathic chemicals also avoided overgrowth by the corallimorpharians. Tentacles along the oral disk margin of R. rhodostoma polyps were swollen and bulbous during contacts with cnidarians. These bulbous marginal tentacles had significantly thicker ectoderm and a higher proportion of holotrichous nematocysts than did the normally filiform marginal tentacles of R. rhodostoma polyps. It is concluded that, on the reef flat at Eilat, this corallimorpharian damages and overgrows a variety of sessile competitors, including branching stony corals, via the application of specialised marginal tentacles filled with penetrating nematocysts. R. rhodostoma is an intermediate competitor in the aggressive hierarchy among Indo-Pacific Anthozoa, including the reef-building corals. Received: 1 July 1998 / Accepted: 24 March 1999