Identifying the largest individual sample value from a two-way composite sampling design

Composite sampling techniques for identifying the largest individual sample value seem to be cost effective when the composite samples are internally homogeneous. However, since it is not always possible to form homogeneous composite samples, these methods can lead to higher costs than expected. In this paper we propose a two-way composite sampling design as a way to improve on the cost effectiveness of the methods available to identify the largest individual sample value.     

南部非洲的一体化电力计划

本文概括了12个南部非洲国家电力联营的一体化电力计划(IEP)过程,阐述了使用IEP的长期计划,本文同时也着重讨论了关于未来生产量的决策过程,提出了有利于在南非采纳更清洁技术的角色和措施.     

城市及其遗产：保存的根源和条件

城市遗产的保存和利用将都市管理的负责人置于艰难选择的境地.下面的文字对城市的构成进行了简短的历史回顾,得出了在场所利用及其保存之间保持平衡发展条件.     

Unprecedented bleaching-induced mortality in Porites spp. at Rangiroa Atoll, French Polynesia

In April-May 1998, mass coral bleaching was observed in the lagoon of Rangiroa Atoll, Tuamotu Archipelago, French Polynesia. Six months later, the extent of bleaching-induced coral mortality was assessed at three sites. Corals in the fast-growing genus Pocillopora had experienced >99% mortality. Many large colonies of the slow-growing genus Porites (mean horizontal cross-sectional area 5.8 m²) had also died - a phenomenon not previously observed in French Polynesia and virtually unprecedented world-wide. At one site, 25% of colonies, or 44% of the pre-bleaching cover of living Porites, experienced whole-colony mortality. At the two other sites, recently dead Porites accounted for 41% and 82% of the pre-bleaching live cover. Mortality in Porites was negatively correlated with depth between 1.5 and 5 m. Using a 50-year dataset of mean monthly sea surface temperature (SST), derived from ship- and satellite-borne instruments, we show that bleaching occurred during a period of exceptionally high summer SST. 1998 was the first year in which mean monthly SSTs exceeded the 1961-1990 upper 95% confidence limit (29.4°C) for a period of three consecutive months. We suggest that the sustained 3-month anomaly in local summer SST was a major cause of coral mortality, but do not discount the synergistic effect of solar radiation. Recovery of the size-frequency distribution of Porites colonies to pre-bleaching levels may take at least 100 years.     

Elevated levels of nitrogen and phosphorus reduce fertilisation success of gametes from scleractinian reef corals

Spawned gametes were collected from colonies of Acropora longicyathus at One Tree Island and Goniastrea aspera at Magnetic Island, Great Barrier Reef, Australia, for use in fertilisation trials. Mean fertilisation rates were significantly reduced compared with controls (P<0.003), when gametes from the branching coral A. longicyathus were exposed to elevated ammonium concentrations at 1 µM and above in one cross (60-64% reduction), and at 100 µM in another cross (16% reduction). Mean fertilisation success of A. longicyathus gametes was also significantly reduced compared with controls in both crosses (P=0.000) at concentrations of 1 µM phosphate and above (35-75% reduction), and at 1 µM ammonium plus 1 µM phosphate and all higher concentrations (68-74% reduction). Similarly, the mean percentage of regular embryos that were developing normally was significantly reduced in most nutrient treatments compared with controls (P=0.000). Fertilisation trials using gametes from the brain coral G. aspera resulted in a significantly lower percentage of regular embryos (P=0.001) and a significantly higher percentage of deformed embryos (P=0.001) developing after exposure to elevated nutrient treatments compared with controls. Mean fertilisation rates for this species were only significantly reduced (P=0.034) in the 50 µM ammonium plus phosphate treatment in one cross (8% reduction), compared with the control. Therefore, ammonium and phosphate enrichment significantly impairs fertilisation success and embryo development in scleractinian reef corals.     

Life on glass houses: sponge stalk communities in the deep sea

Photographs of the deep-sea floor often show organisms attached to biogenic structures that protrude from the soft bottom. In particular, the stalks of glass sponges (hexactinellids) provide hard substrata and act as habitat islands for deep-sea fauna. The primary objectives of this study were to determine the abundance of glass sponge “stalks” at an abyssal station in the NE Pacific, to identify the fauna associated with stalks, and to compare the distribution patterns of epifaunal taxa both horizontally and vertically. Densities of stalks and large epifauna were estimated from analysis of ∼9 km of photographic transects taken in 1994–1995 at station M (34°45′N; 123°00′W; 4,100 m depth) off California, USA. At least 87% of the stalks were the spicule columns of live or dead hexactinellids in the genus Hyalonema (Gray, 1832). Stalks appeared to be distributed randomly across the sea floor (density: 0.13 stalks m⁻²). A colonial zoanthid, Epizoanthus stellaris (Hertwig, 1888), inhabited 20% of the stalks and was the most commonly observed epifaunal organism, followed by other suspension feeders that generally were situated at the top of the structures. Thirty-five stalk communities were collected in tube cores in 1994–1995 using the submersible “Alvin”. A total of 139 taxa was associated with these hard-substratum habitats (another five species were observed only in photographs). Although taxon richness was high, the species diversity of these communities was relatively low due to the dominance in percentage abundance of a foraminiferan, Cibicides lobatulus (Walker and Jakob, 1798), and a serpulid polychaete, Bathyvermilia sp. (Zibrowius, 1973). The relationship between number of taxa and surface area of the stalks yielded a slope (z-value) typical of islands with a low rate of immigration. Three-dimensional complexity created by branching epifauna on the stalks provided more surface area and a variety of cryptic microhabitats. Vertical zonation on the stalks appeared to be controlled by biological interactions among species, with solitary fauna and certain functional groups of colonial organisms restricted by sheet-like colonial organisms that appeared to be dominant space competitors. Received: 13 April 2000 / Accepted: 9 November 2000     

Avian Conservation under the Endangered Species Act: Expenditures versus Recovery Priorities

Abstract: Budget constraints require the U.S. Fish and Wildlife Service to prioritize species for recovery spending. Each listed species is ranked according to the degree of threat it faces, its recovery potential, and its taxonomic distinctness. We analyzed state and federal government expenditures for recovery of threatened and endangered birds ( n = 85 species) from 1992 to 1995 to determine if the priority system was being followed. Although recovery spending correlated with priority rank, priority rank explained <5% of the variation in spending. A small number of the same moderately ranked species dominated expenditures each year (41–79% of total annual budgets). Species with wide distributions, high recovery potential, and captive breeding programs received the most funding, and more funding than their priority ranks dictated. Island species received significantly less funding than expected based on priority rank. Twelve species, 10 of which resided on islands, received <$5000 at least once from 1992 to 1995. Recovery spending was unrelated to degree of threat, taxonomic distinctness, and migratory status. There also was no relationship between land-purchase expenditures and priority ranks. To improve the relationship between recovery spending on threatened and endangered birds and their priority rank, significant changes need to be made within the private sector ( less litigation and special-interest lobbying  ), U.S. Congress (increased budget and reduced earmarking  ), and the U.S. Fish and Wildlife Service (restructuring of regional offices and increased accountability).     

Environmental levels of sediment-associated tri-n-butyltin chloride (TBTCl) and ionic regulation in flounders during seawater adaptation

The effects of exposure to sediment-associated tri-n-butyltin chloride (TBTCl) were examined in the euryhaline European flounder, Platichthys flesus (L.). The effects were quantified by measuring the changes in sodium efflux; Na⁺/K⁺-ATPase activity; and the numbers, areas, and distribution of chloride cells in the gills of freshwater-adapted fish, following a rapid transfer to seawater. Following the transfer to seawater, the Na⁺/K⁺-ATPase activity and the sodium efflux were significantly increased in the control group but remained unchanged in the TBTCl-exposed group. The normal morphological changes to the gill epithelium associated with seawater adaptation, which involve chloride cell distribution, took place in the control group but were significantly inhibited or delayed in the TBTCl group. The results presented in this study lead to the conclusion that environmental concentrations of tri-n-butyltin chloride in sediments are capable of significantly disrupting both the physiological and the morphological components of iono-regulatory functions of an estuarine flatfish.     

Foraging behavior of juvenile Carcinus maenas (L.) and Cancer pagurus L.

Information concerning the way juvenile crabs choose their diet from a variety of prey types can be useful for a better understanding of community dynamics, as well as for the adequate management of natural resources. Prey size and species selection by juvenile Carcinus maenas (15-35 mm carapace width, CW) and Cancer pagurus (20-40 mm CW) feeding on four bivalves of contrasting shell morphology were investigated. When offered a wide size range of Mytilus edulis, Ostrea edulis, Crassostrea gigas, and Cerastoderma edule presented individually, crabs generally showed evidence of size-selective predation. Cancer pagurus selected larger mussels relative to the size of their chelae (relative prey size, RPS) than did Carcinus maenas of similar and even larger carapace width. However, the RPS of selected O. edulis and Cerastoderma edule were similar for all crabs, suggesting that certain prey features constitute effective barriers even to the powerful chelae of Cancer pagurus. When offered a wide size range of mussels and oysters simultaneously, all crabs consistently selected mussels. When offered O. edulis and Crassostrea gigas, crabs consumed both these oyster species in similar numbers. Carcinus maenas consumed similar numbers of mussels and cockles; Cancer pagurus, however, showed no preference for either prey in the smaller size classes but selected more mussels than cockles as prey increased in size. Although previous studies report that adult Carcinus maenas select prey species according to their profitability (amount of food ingested per unit of handling time, milligrams per second), consumption rates of the size classes of prey selected by juvenile shore crabs did not always parallel prey value. Although variations in crab strength can account for many of the differences between the foraging strategy of juvenile and adult C. maenas, our results suggest that juvenile crabs are less species selective than adults as a result of the restrictions imposed on small individuals that have limited access to larger prey.