Zonal management of arsenic contaminated ground water in Northwestern Bangladesh

This paper used ordinary kriging to spatially map arsenic contamination in shallow aquifers of Northwestern Bangladesh (total area  35,000 km²). The Northwestern region was selected because it represents a relatively safer source of large-scale and affordable water supply for the rest of Bangladesh currently faced with extensive arsenic contamination in drinking water (such as the Southern regions). Hence, the work appropriately explored sustainability issues by building upon a previously published study (Hossain et al., 2007; Water Resources Management, vol. 21: 1245–1261) where a more general nation-wide assessment afforded by kriging was identified. The arsenic database for reference comprised the nation-wide survey (of 3534 drinking wells) completed in 1999 by the British Geological Survey (BGS) in collaboration with the Department of Public Health Engineering (DPHE) of Bangladesh. Randomly sampled networks of zones from this reference database were used to develop an empirical variogram and develop maps of zonal arsenic concentration for the Northwestern region. The remaining non-sampled zones from the reference database were used to assess the accuracy of the kriged maps. Two additional criteria were explored: (1) the ability of geostatistical interpolators such as kriging to extrapolate information on spatial structure of arsenic contamination beyond small-scale exploratory domains; (2) the impact of a priori knowledge of anisotropic variability on the effectiveness of geostatistically based management. On the average, the kriging method was found to have a 90% probability of successful prediction of safe zones according to the WHO safe limit of 10 ppb while for the Bangladesh safe limit of 50 ppb, the safe zone prediction probability was 97%. Compared to the previous study by Hossain et al. (2007) over the rest of the contaminated country side, the probability of successful detection of safe zones in the Northwest is observed to be about 25% higher. An a priori knowledge of anisotropy was found to have inconclusive impact on the effectiveness of kriging. It was, however, hypothesized that a preferential sampling strategy that honored anisotropy could be necessary to reach a more definitive conclusion in regards to this issue.     

The interaction between seaweed farming as an alternative occupation and fisher numbers in the central Philippines

Alternative occupations are frequently promoted as a means to reduce the number of people exploiting declining fisheries. However, there is little evidence that alternative occupations reduce fisher numbers. Seaweed farming is frequently promoted as a lucrative alternative occupation for artisanal fishers in Southeast Asia. We examined how the introduction of seaweed farming has affected village-level changes in the number of fishers on Danajon Bank, central Philippines, where unsustainable fishing has led to declining fishery yields. To determine how fisher numbers had changed since seaweed farming started, we interviewed the heads of household from 300 households in 10 villages to examine their perceptions of how fisher numbers had changed in their village and the reasons they associated with these changes. We then asked key informants (people with detailed knowledge of village members) to estimate fisher numbers in these villages before seaweed farming began and at the time of the survey. We compared the results of how fisher numbers had changed in each village with the wealth, education, seaweed farm sizes, and other attributes of households in these villages, which we collected through interviews, and with village-level factors such as distance to markets. We also asked people why they either continued to engage in or ceased fishing. In four villages, respondents thought seaweed farming and low fish catches had reduced fisher numbers, at least temporarily. In one of these villages, there was a recent return to fishing due to declines in the price of seaweed and increased theft of seaweed. In another four villages, fisher numbers increased as human population increased, despite the widespread uptake of seaweed farming. Seaweed farming failed for technical reasons in two other villages. Our results suggest seaweed farming has reduced fisher numbers in some villages, a result that may be correlated with socioeconomic status, but the heterogeneity of outcomes is consistent with suggestions that alternative occupations are not a substitute for more direct forms of resource management.     

Microbial consortia increase thermal tolerance of corals

This study examined the response of a coral holobiont to thermal stress when the bacterial community was treated with antibiotics. Colonies of Pocillopora damicornis were exposed to broad and narrow-spectrum antibiotics targeting coral-associated α and γ-Proteobacteria. Corals were gradually heated from the control temperature of 26 to 31 °C, and measurements were made of host, zooxanthellar and microbial condition. Antibiotics artificially reduced the abundance and activity of bacteria, but had minimal effect on zooxanthellae photosynthetic efficiency or host tissue protein content. Heated corals without antibiotics showed significant declines in F _V /F _M , typical of thermal stress. However, heated corals treated with antibiotics showed severe tissue loss in addition to a decline in F _V /F _M . This study demonstrated that a disruption to the microbial consortium diminished the resilience of the holobiont. Corals exposed to antibiotics under control temperature did not bleach, suggesting that temperature may be an important factor influencing the activity, diversity and ecological function of the holobiont bacterial community.     

Matching and mismatching stable isotope (δ13C and δ15N) ratios in fin and muscle tissue among fish species: a critical review

Using non-lethal tissue sampling for stable isotope analysis has become standard in many fields, but not for fishes, despite being desirable when species are rare or protected, when repeated sampling of individuals is required or where removal may bias other analyses. Here, we examine the utility of fish dorsal fin membrane as an alternative to muscle for analyzing δ¹³C and δ¹⁵N ratios in two reef fish species (blue cod Parapercis colias and spotty Notolabrus celidotus) that have differing feeding modes. Both species exhibited evidence of size-based feeding from fin δ¹⁵N values, but not from muscle. Blue cod fin δ¹⁵N increased steadily throughout the sampled size range (213–412 mm fork length), whereas spotty exhibited a distinct ontogenetic diet shift at approximately 120–140 mm fork length after which size-based feeding did not occur. Fin membrane was higher than muscle in δ¹³C in both species and in δ¹⁵N for blue cod, but fin δ¹⁵N was lower than muscle in spotty. The δ¹³C and δ¹⁵N fin–muscle offsets were constant in spotty regardless of size, while in blue cod, δ¹³C was constant with fish size, but δ¹⁵N offsets increased with increasing fish size. Non-lethal sampling utilizing fin tissue can be employed to estimate stable isotope values of muscle in fishes, but it is necessary to assess relationships among tissues and the effects of fish size on isotope values a priori for each species studied. Our data indicated that fin membrane may be a more sensitive tissue than muscle for detecting size-based feeding in some fish species using stable isotopes. A critical literature review revealed inconsistencies in tissue types tested, little understanding of tissue-specific trophic shift or turnover rates, and pseudo-replicated analyses leading to erroneous postulating of 1:1 relationships between tissues.     

Host selection by a kleptobiotic spider

Why do kleptobiotic spiders of the genus Argyrodes seem to be associated with spiders of the genus Nephila worldwide? Observations following introduction of experimental insect prey of different sizes and weights on to host webs revealed that: (1) small prey are more effectively retained on the web of Nephila clavipes than on the web of another common host, Leucauge venusta. (2) N. clavipes did not consume small prey that accumulated on the web whereas larger, heavier prey were enveloped and stored. (3) We observed clear partitioning of prey items between N. clavipes and Argyrodes spp.; diet selection by Argyrodes did not overlap with that of N. clavipes but closely overlapped with that of L. venusta. (4) L. venusta responds very quickly to prey impact whereas N. clavipes is slower, offering a temporal window of opportunity for Argyrodes foraging. (5) The ability of L. venusta to detect and respond to small items also means that it acts aggressively to Argyrodes spp., whereas N. clavipes does not. Consequently, food-acquisition behaviours of Argyrodes were clearly less risky with N. clavipes compared with L. venusta. We conclude that when a kleptobiotic organism has a choice of various host species, it will opt for the least risky host that presents the highest rate of availability of food items. The fact that Nephila species present such characteristics explains the worldwide association with Argyrodes kleptobiotic spiders.     

A decision tree for Coastal Management permit guidelines

The Louisiana Coastal Management Division (CMD) uses over 90 guidelines for permitting construction activities in the coastal zone. The use of the guidelines by, the CMD staff is not always systematically applied to permit applications. A set of guideline decision trees was, therefore, developed for the permit review process using a structural modeling technique. A decision tree provides the framework for optimizing the decision process. The order in which decisions are made contributes to the efficiency and uniformity of the process. The result provides a more timely and consistent review of most permit applications regarding mining, hazardous wastes, levees, and zoning.