Stable isotopic investigation of physiological and environmental changes recorded in shell carbonate from the giant clam Tridacna maxima

The aragonitic shell of the photosymbiont-bearing bivalve Tridacna maxima contains a record of the physiological and environmental changes the organism has experienced during its lifetime. This record is preserved as chemical and microstructural variations throughout the shell. Stable isotopic analyses of oxygen (¹⁸O/¹⁶O) and carbon (¹³C/¹²C) in shell carbonate were combined with growth increment studies to interpret the shell record of specimens collected from the Rose Atoll (Lat. 14°31S; Long. 168°10W) in April 1982. The seasonal water temperature cycle is recorded in the oxygen isotopic signature of the clams, permitting the recognition of annual cycles in the ¹⁸O profile. The total number of these cycles corresponds to the age of a specimen, while the cycle length is a measure of the yearly growth rate. Large-amplitude cycles, reflecting year-round calcification, characterize the early portion of the growth record. With the onset of sexual maturity and slower growth at an age of approximately ten years, the cycles decrease in amplitude and become more erratic. During this later growth phase calcification is limited to the cooler months of the year, perhaps in response to a re-ordering of energy priorities between growth and gametogenesis. A growth curve developed from the ¹⁸O profile indicates rapid juvenile shell growth followed by slower growth thereafter producing a lifespan of several decades. Carbon isotopic analyses of T. maxima were compared to analyses of the symbiont-barren gastropod Terebra areolata collected from the same locality in April 1984. A 2 depletion in the ¹³C composition of T. maxima shell carbonate is attributed to a symbiontenhanced metabolic rate and an increased flow of isotopically light, respired CO₂ into the carbon pool used in calcification. Such a depletion may prove useful in identifying the presence of photosymbionts in extinct species of fossil mollusks.     

Limited evidence for increased cold-tolerance of invasive versus native <Emphasis Type="Italic">Caulerpa taxifolia</Emphasis>

Growth characteristics of native and invasive Caulerpa taxifolia from coastal eastern Australia were compared in warm (22–25°C) and cool (15–18°C) water in two laboratory experiments. Measurements of biomass, stolon length, mean frond length and numbers of fronds and stolon meristems, demonstrated that the growth of native and invasive C. taxifolia in warm water was up to ten times greater than in cool water. Growth rates differed substantially among locations over 9 weeks, but for most variables, the growth of native C. taxifolia was greater than the growth of invasive C. taxifolia in warm water. In cool water, there was little difference in growth of invasive versus native C. taxifolia. The morphology of C. taxifolia changed considerably in response to temperature, such that native and invasive samples that were morphologically distinct at the start of the experiment became indistinguishable after 69 days in warm water. We concluded there was little evidence that the C. taxifolia which recently invaded temperate estuaries in New South Wales could spread faster in cool water than could native C. taxifolia from Queensland. Native tropical C. taxifolia appears tolerant of a wide range of environmental conditions and seems capable of surviving and becoming invasive in temperate estuaries.     

Ecological impacts on the limpet Lottia gigantea populations: human pressure over a broad scale on island and mainland intertidal zones

Here long-term monitoring data taken at 33 sites in southern and central California coast and islands were used to evaluate the size structure of the large intertidal limpet, Lottia gigantea in restricted-access and in easily accessible intertidal zones that encompass a wide range of ecological variables. Using multi-dimensional analysis of population size structures, we found that sites on islands and strictly protected mainland sites have significantly larger median limpet sizes and a greater range of limpet sizes than unprotected mainland sites, while no pattern occurs in latitudinal or regional comparison of sites. Although intertidal predators such as oystercatchers were not the primary focus of the monitoring efforts, extensive natural history notes taken during sampling visits support the argument that predation was not a primary cause for the size structure differences. Finally, substratum differences were determined not to have biased the observation of larger limpets in protected sites. In regard to human interactions with limpets, we conclude that the degree of enforcement against poaching is the better predictor of limpet size structure than proximity to population centers or visitation to intertidal sites.     

Geophagy in the tropics: an appraisal of three geophagical materials

Geophagy, the deliberate consumption of soil, is a common practice amongst the world's poorer or more tribally oriented people of the tropics. An appraisal of three geophagical samples suggests that Fe is a mineral nutrient which can be supplied to humans in significant amounts via ingested soil. Geophagy provides a direct link between the geochemistry of soils and human health, but as yet this association has only a limited awareness amongst research workers.     

Conservation Implications of the Natural Loss of Lineages in Wild Mammals and Birds

Because populations in zoological parks and nature reserves often are derived from only a few individuals, conservationists have attempted to minimize founder effects by equalizing family group sizes and increasing the reproductive contributions of all individuals. Although such programs reduce potential losses of genetic diversity, information is rarely available about the actual persistence of family groups or genetic lineages in natural populations. In the absence of such data, it can be difficult to weigh the importance of human intervention in the conservation of small populations. Separate long-term studies of two mammals, the North American bison (Bison bison) and the white-nosed coati (Nasua narica), and a bird, the Acorn Woodpecker (Melanerpes formicivorus), demonstrate differential extinction of genetic lineages. Irrespective of the mechanisms affecting population structure, which may range from stochastic environmental events to such behavioral phenomena as poor intrasexual competitive abilities, our results show that lineages can be lost at rapid rates from natural populations. A survey of comparable studies from the literature indicates that the loss of matrilines over the course of the study varies from 3% to 87% in wild mammals and from 30% to 80% in birds, with several small mammals losing approximately 20% of matrilines per year of study. These lineage extinctions were not an artifact of the length of the study or the generation time of the species. Such rapid losses of lineages in less than 20-year periods in natural populations suggest that efforts to maintain maximal genetic diversity within populations may not always reflect processes that occur in the wild. Conservation biologists need to give further thought to the extent to which parity among genetic lines should be a primary goal of management of captive and small wild populations.     

PAHs associated with the leaves of three deciduous tree species. I--Concentrations and profiles

Results for the concentrations of total polycyclic aromatic hydrocarbons (Sigma PAH) and the PAH profile in leaves from three deciduous tree species from the same woodland are presented, and discussed with reference to environmental and leaf-related variables. There were significant differences between oak, ash and hazel leaves in their Sigma PAH concentrations (sum of 23 PAHs), and in the relative contribution of individual PAHs to the sum. Leaves exhibiting pubescence (hairiness) were found to have significantly higher Sigma PAH concentrations than hairless leaves, regardless of their position in the vegetation strata of the wood. Hazel leaves from the understorey had a PAH profile consisting of a greater proportion of the 4-, 5- and 6-ring PAHs than oak or ash from the canopy. This was concluded to be the result of the filtering effect of the main canopy on the air passing over and through it, with subsequent transfer of particles and attendant PAHs to the understorey below. The proportion of Sigma PAH contributed by the 6-ring PAH in hazel leaves was negatively correlated with distance from the southern edge of the canopy. It is proposed that the predominantly windward edges of the woodland, where atmospheric turbulence is likely to be greatest, favoured the deposition of particle-bound PAHs to leaves.     

An approach for assessment of water quality using semipermeable membrane devices (SPMDs) and bioindicator tests

As an integral part of our continued development of water quality assessment approaches, we combined integrative sampling, instrumental analysis of widely occurring anthropogenic contaminants, and the application of a suite of bioindicator tests as a specific part of a broader survey of ecological conditions, species diversity, and habitat quality in the Santa Cruz River in Arizona, USA. Lipid-containing semipermeable membrane devices (SPMDs) were employed to sequester waterborne hydrophobic chemicals. Instrumental analysis and a suite of bioindicator tests were used to determine the presence and potential toxicological relevance of mixtures of bioavailable chemicals in two major water sources of the Santa Cruz River. The SPMDs were deployed at two sites; the effluent weir of the International Wastewater Treatment Plant (IWWTP) and the Nogales Wash. Both of these systems empty into the Santa Cruz River and the IWWTP effluent is a potential source of water for a constructed wetland complex. Analysis of the SPMD sample extracts revealed the presence of organochlorine pesticides (OCs), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). The bioindicator tests demonstrated increased liver enzyme activity, perturbation of neurotransmitter systems and potential endocrine disrupting effects (vitellogenin induction) in fish exposed to the extracts. With increasing global demands on limited water resources, the approach described herein provides an assessment paradigm applicable to determining the quality of water in a broad range of aquatic systems.     

Analysis of halogenated polycyclic aromatic hydrocarbons in urban air, snow and automobile exhaust

Urban air, snow and automobile exhaust samples were extensively cleaned up by open column liquid chromatography. The appropriate fractions were analysed for halogenated polycyclic aromatic hydrocarbons (XPAH) by gas chromatography/negative chemical ionization mass spectrometry (GC/NCIMS). XPAH were found in all three sample types. A urban air sample was found to contain chlorinated pyrenes, fluoranthenes and benzopyrene and brominated pyrenes and fluoranthenes. Furthermore, the concentration of 1-chloropyrene in that air sample was estimated to be 10 pg/m³. XPAH were also found in snow samples taken in the vicinity of a motor-way. Ethylene dibromide and ethylene dichloride, are probably the source of the halogen atoms in the XPAH detected in car exhaust.     

Influence of plants on the chemical extractability and biodegradability of 2,4-dichlorophenol in soil

This study investigated the fate and behaviour of [UL-(14)C] 2,4-dichlorophenol (DCP) in planted (Lolium perenne L.) and unplanted soils over 57 days. Extractability of [UL-(14)C] 2,4-DCP associated activity was measured using calcium chloride (CaCl(2)), acetonitrile-water and dichloromethane (DCM) extractions. Biodegradability of [UL-(14)C] 2,4-DCP associated activity was assessed through measurement of (14)CO(2) production by a degrader inoculum (Burkholderia sp.). Although extractability and mineralisation of [UL-(14)C] 2,4-DCP associated activity decreased significantly in both planted and unplanted soils, plants appeared to enhance the sequestration process. After 57 days, in unplanted soil, 27% of the remaining [UL-(14)C] 2,4-DCP associated activity was mineralised by Burkholderia sp., and 13%, 48%, and 38% of (14)C-activity were extracted by CaCl(2), acetonitrile-water and DCM, respectively. However, after 57 days, in planted soils, only 10% of the [UL-(14)C] 2,4-DCP associated activity was available for mineralisation, whilst extractability was reduced to 2% by CaCl(2), 17% by acetonitrile-water and 11% by DCM. This may be due to the effect of plants on soil moisture conditions, which leads to modification of the soil structure and trapping of the compound. However, the influence of plants on soil biological and chemical properties may also play a role in the ageing process.