Ultraviolet radiation effects on the behavior and recruitment of larvae from the reef coral Porites astreoides

We tested the rarely considered hypothesis that the ultraviolet portion (UVR, 280–400 nm) of the light spectrum affects patterns of recruitment in reef-building corals. The premise for this hypothesis rests in the fact that biologically relevant intensities of UVR penetrate to considerable depths (>24 m) in the clear waters surrounding many coral reefs, and that reef organisms allocate substantial resources to prevent and repair UVR damage. The ability of larvae spawned by the brown morph of the Caribbean coral, Porites astreoides, to detect and avoid UVR was assessed in petri dishes where one-half of the dish was shielded from UVR and the other exposed. Observations made every 30 min between 10:30 and 13:30 h showed significantly higher densities of larvae swimming in regions shielded from UVR. To determine how this behavior affects settlement patterns, larvae collected from P. astreoides adults at 18 m depth were released into chambers deployed at 17 m depth where they were given a choice of three different light regions in which to settle: PAR (PAR=400–700 nm), PAR+UVAR (UVAR=320–400 nm), and PAR+UVAR+UVBR (UVBR=280–320 nm). At the end of the experiment, greater numbers of P. astreoides larvae had settled in the region of the tube where UVR was reduced than would be expected if dispersion were random. To our knowledge, this is the first demonstration in any reef-building coral species that planula larvae can detect UVR and that it affects their choice of a settlement site. These results indicate that the capacity to detect and avoid habitats with biologically damaging levels of UVR may be one factor contributing to the successful recruitment of coral larvae.     

Evidence that reef-wide patterns of coral bleaching may be the result of the distribution of bleaching-susceptible clones

The hypothesis that intraspecific variation in coral bleaching is a result of the distribution of bleaching-susceptible clonal genotypes (genets) was addressed using photoquadrats recorded during the 1987 Caribbean bleaching event on a reef dominated by Montastraea annularis (Morphotype I), together with manipulative experiments with Porites porites. Nearest-neighbor analysis showed that bleached colonies (ramets) of M. annularis at 10 m depth had a high probability (0.80) of having a nearest bleached neighbor of the same genet rather than a bleached ramet of a different genet. Furthermore, the frequency distributions of bleached ramets of M. annularis in the photoquadrats was significantly different from a Poisson distribution, suggesting that bleached ramets were aggregated on the reef. Manipulative experiments with P. porites from 15 m depth showed that some genets were more susceptible to thermal bleaching than others, since three genets had significantly different rates of zooxanthellae loss when exposed to elevated temperatures in tanks receiving irradiances similar to those found in situ. These results suggest that the in situ patchy distribution of bleached ramets could correspond to the distribution of certain genets, and that adjacent genets can exhibit sufficiently different phenotypes to account for intraspecific variation in bleaching. Further studies of genet-specific coral bleaching may provide valuable insights into the causes and consequences of bleaching.     

Groundwater chemistry and the Balkan endemic nephropathy

Until now failure has been a common feature of all attempts to elucidate the aetiology of Balkan endemic nephropathy (BEN), a peculiar kidney disease known to exist only in south-eastern Europe. However, whatever the cause, many epidemiological data point to water as a vehicle of the unknown agent(s). We addressed the issue by reexamining multielement hydrogeochemical data obtained by one of us (WME) in the field, as well as other relevant pieces of evidence.Well water samples were obtained from 18 households heavily affected by BEN, and situated in nine villages scattered over six distinct endemic areas. Control samples were taken from non-affected households exposed to the BEN environment (2), as well as from neighbouring non-endemic villages (5).In terms of the chemical composition of well water, considerable differences between the areas were observed. As a rule the water chemistry of BEN-affected households was rather similar to control samples but there were large variations within each of the two groups.Though none of the wide range of geochemical and hydrogeological parameters have been positively implicated as related to BEN, water-borne chemicals still remain a clue to be pursued, particularly in relation to ultratrace concentrations of bioessential elements and organics.     

Evaluating the causal basis of ecological success within the scleractinia: an integral projection model approach

Many tropical corals have declined in abundance in the last few decades, and evaluating the causal basis of these losses is critical to understanding how coral reefs will change in response to ongoing environmental challenges. Motivated by the likelihood that marine environments will become increasingly unfavorable for coral growth as they warm and become more acidic (i.e., ocean acidification), it is reasonable to evaluate whether specific phenotypic traits of the coral holobiont are associated with ecological success (or failure) under varying environmental conditions including those that are adverse to survival. Initially, we asked whether it was possible to identify corals that are resistant or sensitive to such conditions by compiling quantitative measures of their phenotypic traits determined through empirical studies, but we found only weak phenotypic discrimination between ecological winners and losers, or among taxa. To reconcile this outcome with ecological evidence demonstrating that coral taxa are functionally unequal, we looked beyond the notion that phenotypic homogeneity arose through limitations of empirical data. Instead, we examined the validity of contemporary means of categorizing corals based on ecological success. As an alternative means to distinguish among functional groups of corals, we present a demographic approach using integral projection models (IPMs) that link organismal performance to demographic outcomes, such as the rates of population growth and responses to environmental stress. We describe how IPMs can be applied to corals so that future research can evaluate within a quantitative framework the extent to which changes in physiological performance influence the demographic underpinnings of ecological performance.     

Effect of sub-lethal damage to juvenile colonies of massive Porites spp. under contrasting regimes of temperature and water flow

In this study, juvenile colonies of massive Porites spp. (a combination of P. lutea and P. lobata) from the lagoon of Moorea (W 149°50′, S 17°30′) were damaged and exposed to contrasting conditions of temperature and flow to evaluate how damage and abiotic conditions interact to affect growth, physiological performance, and recovery. The experiment was conducted in April and May 2008 and consisted of two treatments in which corals were either undamaged (controls) or damaged through gouging of tissue and skeleton in a discrete spot mimicking the effects of corallivorous fishes that utilize an excavating feeding mode. The two groups of corals were incubated for 10 days in microcosms that crossed levels of temperature (26.7 and 29.6°C) and flow (6 and 21 cm s⁻¹), and the response assessed as overall colony growth (change in weight), dark-adapted quantum yield of PSII (F _v/F _m), and healing of the gouged areas. The influence of damage on growth was affected by temperature, but not by flow. When averaged across flow treatments, damage promoted growth by 25% at 26.7°C, but caused a 25% inhibition at 29.6°C. The damage also affected F _v/F _m in a pattern that differed between flow speeds, with a 10% reduction at 6 cm s⁻¹, but a 4% increase at 21 cm s⁻¹. Regardless of damage, F _v/F _m at 21 cm s⁻¹ was 11% lower at 26.7°C than at 29.6°C, but was unaffected by temperature at 6 cm s⁻¹. The lesions declined in area at similar rates (4–5% day⁻¹) under all conditions, although the tissue within them regained a normal appearance most rapidly at 26.7°C and 6 cm s⁻¹. These findings show that the response of poritid corals to sub-lethal damage is dependent partly on abiotic conditions, and they are consistent with the hypothesis that following damage, calcification and photosynthesis can compete for metabolites necessary for repair, with the outcome affected by flow-mediated mass transfer. These results may shed light upon the ways in which poritid corals respond to biting by certain corallivorous fishes.     

Trade-offs in assessing environmental impacts

Summary The evolution of the environmental issue has moved through the early stage of technological fixes and estimable economic costs into an area of larger uncertainty and higher information costs.The economic costs of pollution control are about one percent of the GNP. The technological fixes have improved air and water quality somewhat; but in air quality little reduction in nitrogen oxides has been achieved, and in water quality about 25 percent of the water is poor or worse, with high fecal coliform bacteria.The next stage of environmental improvement is to reduce hazardous chemical elements in the environment. In these areas, the health and biological effects are still uncertain, information costs are high, and subjective judgments are common.As uncertainty and qualitative judgments have become more prominent in environmental decisions, delays have been introduced into the decision loops, raising regulatory costs, and heightening adversary stresses between business and environmentalists. The stresses place an aura of arbitrariness over regulations in a milieu where the governability of society is already questioned. This is not the time to retreat from environmental improvement, but to try to simplify the decision process. Two possible alternatives are to codify court precedents into a more rigorous reliance on agency administration law, or to revert to the common rules of civil law that complainants must show damage and cause before an award is allowable by an administrative agency. Either of these options would free the decision making process of delays and allow it to function prospectively, while allowing environmental damages from inadequate decisions to be remedied retroactively. Potential liabilities may increase, but at least the decision process could move forward without being frustrated by regulatory delays.