100s Of Km Research Articles

Rapid Biodiversity Assessment and Monitoring Method for Highly Diverse Benthic Communities: A Case Study of Mediterranean Coralligenous Outcrops

Increasing anthropogenic pressures urge enhanced knowledge and understanding of the current state of marine biodiversity. This baseline information is pivotal to explore present trends, detect future modifications and propose adequate management actions for marine ecosystems. Coralligenous outcrops are a highly diverse and structurally complex deep-water habitat faced with major threats in the Mediterranean Sea. Despite its ecological, aesthetic and economic value, coralligenous biodiversity patterns are still poorly understood. There is currently no single sampling method that has been demonstrated to be sufficiently representative to ensure adequate community assessment and monitoring in this habitat. Therefore, we propose a rapid non-destructive protocol for biodiversity assessment and monitoring of coralligenous outcrops providing good estimates of its structure and species composition, based on photographic sampling and the determination of presence/absence of macrobenthic species. We used an extensive photographic survey, covering several spatial scales (100s of m to 100s of km) within the NW Mediterranean and including 2 different coralligenous assemblages: Paramuricea clavata (PCA) and Corallium rubrum assemblage (CRA). This approach allowed us to determine the minimal sampling area for each assemblage (5000 cm2 for PCA and 2500 cm2 for CRA). In addition, we conclude that 3 replicates provide an optimal sampling effort in order to maximize the species number and to assess the main biodiversity patterns of studied assemblages in variability studies requiring replicates. We contend that the proposed sampling approach provides a valuable tool for management and conservation planning, monitoring and research programs focused on coralligenous outcrops, potentially also applicable in other benthic ecosystems.

Habitat heterogeneity in eelgrass fish assemblage diversity and turnover

ABSTRACT Maintaining habitat diversity and heterogeneity are key ecological elements of marine spatial planning. It is often assumed that patches of the same habitat harbour similar biological diversity. However, if habitat heterogeneity is high then the efficacy of habitats as surrogates of species diversity is weakened. Beta diversity variation in fish assemblages in eelgrass meadows along the Pacific coast of Canada was analysed using permutational multivariate analysis of variance and tests for dispersion of homogeneity. Variations in species composition were examined at an inter‐regional scale (100 s of km apart) and an intra‐regional scale (10s of km apart) over 7 years. Further, similarity percentage analysis and biological‐environmental modelling were used to identify factors that differentiated among fish assemblages. Beta diversity turnover was also considered by examining for the decay in fish assemblage similarity across gradients in sea surface temperature, salinity, and physical distance between pairs‐of‐meadows using linear regression. Patches of eelgrass meadows exhibited high fish assemblage dissimilarity at both the intra‐regional and inter‐regional scales; spatial factors accounted for substantially more variation in fish composition than temporal factors. A large number of fish species (20–30) and different suites of environmental factors accounted for the observed high beta diversity variation. Fish composition similarity did not decay consistently within each region with physical distance between meadows or with a change of 1°C in temperature, but Jaccard similarity did decay significantly within each region by 2–4% per part per thousand change in salinity. It is recommended that marine protected area planners consider the influence of freshwater flow into the coastal ocean and its subsequent impact on environmental gradients, which drives fish assemblage heterogeneity among eelgrass habitat patches. Copyright © 2011 John Wiley & Sons, Ltd.

Obduction of Tethyan-type ophiolites—A case-study from the Thetford-Mines ophiolitic Complex, Quebec Appalachians, Canada

Oceanic plagiogranites and peridotite-hosted granites (PHG) of the Thetford-Mines ophiolite (TMO) yield mean U–Pb zircon ages of 479.2±1.6Ma and 469.5±2.8Ma, and are interpreted to be the products of fractionation of basaltic magma and melting of the Laurentian margin, respectively. The existing 40Ar/39Ar age for the ophiolitic metamorphic sole of the TMO is a hornblende isochron age of 477±5Ma for amphibolite facies rocks. Sites previously sampled for U–Pb and 39Ar–40Ar analyses were resampled for more accurate 39Ar–40Ar dating, in order to better constrain the thermo-tectonic evolution of the ophiolite and underlying Laurentian margin rocks on which they were overthrust, and quantify the time required for obduction of Tethyan-type ophiolites in the Canadian Appalachians. Amphiboles from TMO gabbro and plagiogranite yield 39Ar–40Ar plateau ages of 477–475Ma. In contrast, muscovites from PHG yield cooling ages of 466–465Ma, and show evidence for thermal resetting at ca. 460Ma for both a granitic mylonite and a crosscutting pegmatite facies. The amphibolitic metamorphic sole yields 39Ar–40Ar ages of ca. 471Ma in amphibole, and high-temperature ages of ca. 466Ma in muscovite, with evidence for recrystallization to ages as young as 457Ma. Muscovites from the sub-ophiolitic Laurentian metasedimentary basement, and micaschist clasts in supraophiolitic debris flows of the TMO, yield similar pseudo-plateau and high-temperature ages of ca. 463–464Ma. The U–Pb and 39Ar–40Ar data suggest that the obduction of peri-Laurentian oceanic crust lasted approximately 5 to 10 m.y. Since both facies formed approximatelym.y. after the ophiolitic crust, this supports models whereby the still-hot ophiolitic mantle provided the heat needed to generate the PHG and the metamorphic sole between ca. 475 and 470Ma. Muscovite ages of PHG record cooling below ca. 450–500°C by ca. 465Ma, but 39Ar–40Ar ages from both a mylonitized PHG facies and micaschist clasts suggest that the emplacement of the oceanic lithosphere on the Laurentia margin had nearly ended by ca. 460Ma, likely due to foreland-directed downward thrust propagation and related exhumation of the collisional wedge. The new age data imply that the southern Quebec ophiolites were thrust 100s of km over the Laurentian margin, which has major implications for the location of the subduction suture and the early stages of the Taconic orogeny in the Northern Appalachians.

Comments on the paper “Is the track of the Yellowstone hotspot driven by a deep mantle plume? — Review of volcanism, faulting, and uplift in light of new data” by Kenneth Pierce and Lisa Morgan [J. Volcanol. Geotherm. Res. 188 (2009), 1–25

The global mid-ocean ridge (MOR) system represents a major site for outgassing of volatiles from Earth's mantle. The amount of H2O released via eruption of mid-ocean ridge basalts varies along the global ridge system and greatest at sites of interaction with mantle plumes. These deep-sourced thermal anomalies affect approximately one-third of all MORs – as reflected in enrichment of incompatible trace elements, isotope signatures and elevated ridge topography (excess melting) – but the physical mechanisms involved are controversial. The “standard model” involves solid-state flow interaction, wherein an actively upwelling plume influences the divergent upwelling generated by a mid-ocean ridge so that melting occurs at higher pressures and in greater amounts than at a normal spreading ridge. This model does not explain, however, certain enigmatic features including linear volcanic ridges radiating from the active plume to the nearby MOR. Examples of these are the Wolf–Darwin lineament (Galápagos), Rodrigues Ridge (La Réunion), Discovery Ridge (Discovery), and numerous smaller ridge-like structures associated with the Azores and Easter–Salas y Gómez hot spots. An important observation from our study is that fractionation-corrected MORB with exceptionally-high H2O contents (up to 1.3 wt.%) are found in close proximity to intersections of long-lived plume-related volcanic lineaments with spreading centres.New algorithms in the rare-earth element inversion melting (INVMEL) program allow us to simulate plume–ridge interactions by mixing the compositions of volatile-bearing melts generated during both active upwelling and passively-driven corner-flow. Our findings from these empirical models suggest that at sites of plume–ridge interaction, moderately-enriched MORBs (with 0.2–0.4 wt.% H2O) result from mixing of melts formed by: (i) active upwelling of plume material to minimum depths of ∼35 km; and (ii) those generated by passive melting at shallower depths beneath the ridge. The most volatile-rich MORB (0.4–1.3 wt.% H2O) may form by the further addition of up to 25% of “deep” small-fraction plume stem melts that contain >3 wt.% H2O. We propose that these volatile-rich melts are transported directly to nearby MOR segments via pressure-induced, highly-channelised flow embedded within a broader “puddle” of mostly solid-state plume material, spreading beneath the plate as a gravity flow. This accounts for the short wavelength variability (over 10s of km) in geochemistry and bathymetry that is superimposed on the much larger (many 100s of km) “waist width” of plume-influenced ridge.Melt channels may constitute a primary delivery mechanism for volatiles from plume stems to nearby MORs and, in some instances, be expressed at the surface as volcanic lineaments and ridges. The delivery of small-fraction hydrous melts from plume stems to ridges via a two-phase (melt-matrix) regime implies that a parallel, bimodal transport system is involved at sites of plume–ridge interaction. We estimate that the rate of emplacement of deep-sourced volatile-rich melts in channels beneath the volcanic lineaments is high and involves 10s of thousands of km3/Ma. Since mantle plumes account for more than half of the melt production at MORs our findings have important implications for our understanding of deep Earth volatile cycling.

Inter-community variability in total particle number concentrations in the eastern Los Angeles air basin

Abstract. Ultrafine Particles (UFP) can display sharp gradients in their number concentrations in urban environment due to their transient nature and rapid atmospheric processing. The ability of using air pollution data generated at a central monitoring station to assess exposure relies on our understanding of the spatial variability of a specific pollutant associated with a region. High spatial variation in the concentrations of air pollutants has been reported at scales of 10s of km for areas affected by primary emissions. Spatial variability in particle number concentrations (PNC) and size distributions needs to be investigated, as the representativeness of a monitoring station in a region is premised on the assumption of homogeneity in both of these metrics. This study was conducted at six sites, one in downtown Los Angeles and five located about 40–115 km downwind in the receptor areas of Los Angeles air basin. PNC and size distribution were measured using Condensation Particle Counters (CPC) and Scanning Mobility Particle Sizer (SMPS). The seasonal and diurnal variations of PNC implied that PNC might vary significantly with meteorological conditions, even though the general patterns at the sites may remain generally similar across the year due to consistency of sources around them. Regionally transported particulate matter (PM) from upwind urban areas of Los Angeles lowered spatial variation by acting as a "homogenizing" factor during favorable meteorological conditions. Spatial variability also increased during hours of the day during which the effects of local sources predominate. The spatial variability associated with PNC (quantified using Coefficients of Divergence, CODs), averaged about 0.3, which was generally lower than that based on specific size ranges. Results showed an inverse relationship of COD with particles size, with fairly uniform values in the particle range which is associated with regional transport. Our results suggest that spatial variability, even in the receptor regions of Los Angeles Basin, should be assessed for both PNC and size distributions, and should be interpreted in context of seasonal and diurnal influences, and suitably factored if values for exposure are ascertained using a central monitoring station.

Conservation genetics, foraging distance and nest density of the scarce Great Yellow Bumblebee (Bombus distinguendus)

The conservation genetics of bees is of particular interest because many bee species are in decline, so jeopardizing the essential ecosystem service of plant pollination that they provide. In addition, as social haplodiploids, inbred bees may be vulnerable to the extra genetic load represented by the production of sterile diploid males. Using microsatellite markers, we investigated the genetic structure of populations of the Great Yellow Bumblebee (Bombus distinguendus Morawitz) in the UK, where this species has undergone a precipitous decline. By means of a mixture of analytical methods and simulation, we also extended--and then applied--genetic methods for estimating foraging distance and nest density in wild bees. B. distinguendus populations were characterized by low expected heterozygosity and allelic richness, inbreeding coefficients not significantly different from zero, absence of detected diploid males, absence of substantial demographic bottlenecking, and population substructuring at large (c. 100+ km) but not small (10s of km) spatial scales. The minimum average effective population size at our sampling sites was low (c. 25). In coastal grassland (machair), the estimated modal foraging distance of workers was 391 m, with 95% of foraging activity occurring within 955 m of the nest, and estimated nest density was 19.3 nests km(-2). These findings show that B. distinguendus exhibits some genetic features of scarce, declining or fragmented populations. Moreover, B. distinguendus workers appear to forage over above-average distances and nests remain thinly distributed even in current strongholds. These considerations should inform future conservation actions for this and similar species.

Miocene Kareem Sequence, Gulf of Suez, Egypt

ABSTRACTThe Miocene Kareem Formation in the Egyptian Gulf of Suez, and its equivalent formations throughout the Red Sea (250–550 m thick), contain one of the most important petroleum reservoirs in these highly faulted rift basins. They present a difficult exploration target, particularly over the shelves of the sparsely explored Red Sea for several reasons: (1) water depth exceeds one kilometer, (2) they underlie thick evaporites (including salt exceeding one kilometer in thickness), (3) they are difficult to image by conventional seismic techniques, and (4) their lithology is laterally variable and difficult to predict (anhydrite, carbonate, sandstone, shale and marl). The target Red Sea formations are best controlled by boreholes in the Gulf of Suez, where the Kareem Formation and its members are characterized by various synonymous units. A review of representative data and interpretations shows that the formation and its members are better understood when considered as a third-order, transgressive-regressive (T-R) depositional sequence, named the Kareem Sequence in the Middle East Geologic Time Scale (ME GTS). The Sequence is bounded above by the Belayim Sequence Boundary (Sub-Belayim Unconformity) and below by the Kareem Sequence Boundary (Sub-Kareem Unconformity), both corresponding to major sea-level lowstands. It contains the Arabian Plate Langhian Maximum Flooding Surface Neogene 30 (MFS Ng30) at the top of the Kareem Maximum Flooding Interval (MFI). Its lower Rahmi Member forms the majority of the transgressive systems tract (TST). The Kareem MFI and regressive systems tract (RST or HST) occur within the upper Shagar Member. The paleontology of the Formation is characterized by Planktonic Foraminiferal Zone N9 and in recent papers also N8, and Calcareous Nannofossil Biozone NN5, but the Formation’s assignment to Miocene stages (Burdigalian, Langhian and Serravallian) is unresolved in the literature.In this paper, the Kareem Sequence is interpreted in terms of Kareem subsequences 1 to 6. At semi-regional scales (10s of km), the older three are each represented by an anhydrite bed (Rahmi Anhydrite 1 to 3, each c. 10 m thick) overlain by deep-marine deposits (shale, marl and carbonate, 10s of meters thick). Subsequences 4 to 6 are represented in El Morgan field (Kareem A to C units), and in representative boreholes, by three deep-marine shale/marl units, each of which is overlain by a regressive shallow-marine sandstone unit. The Kareem Sequence is correlated to third-order orbital sequence DS3 1.1 with a depositional period of ca. 2.43 million years between ca. 16.1 and 13.7 million years before present (Ma), or numerically the latest Burdigalian, Langhian and earliest Serravallian (Langhian: 15.97–13.65 Ma in GTS 2004; 15.97–13.82 Ma in GTS 2009). The six subsequences are correlated to the orbital 405,000 year eccentricity cycle (referred to as Stratons 40–35 or DS4 1.1.1 to 1.1.6). The older three subsequences form the transgressive systems tract; the fourth contains the maximum flooding interval MFI (ca. 14.9–14.7 Ma) in its lower part. The regressive systems tract starts in the upper part of the fourth subsequence and encompasses subsequences 5 and 6. The orbital architecture of the Sequence provides a simplified framework for predicting lithology and reservoir development.The six Kareem subsequences carry the orbital-forcing glacio-eustatic signal. During low eccentricity, Antarctic ice-making and global sea-level drops, the northernmost Gulf of Suez and Bab Al Mandeb Strait restricted marine circulation in the Gulf and Red Sea rift basins. The resulting evaporitic setting was associated with the deposition of the Rahmi Anhydrite 1 to 3 beds and exposure over paleohighs. The deeper-marine deposits above the three Rahmi Anhydrite beds, and those of subsequences 4 to 6 reflect high eccentricity, Antarctic ice-melting, global sea-level rises, pluvial conditions at low latitudes (10–30oN), and open-marine circulation in the Red Sea. During pluvial periods, fluvio-deltaic systems prevailed over the mountainous rift shoulders and coastal plains and carried massive clastics into the Gulf and Red Sea Basins.

Scales of habitat heterogeneity and megabenthos biodiversity on an extensive Australian continental margin (100–1100 m depths)

AbstractThe first large systematic collection of benthic invertebrate megafauna from the Australian continental margin (depths > 100 m) revealed high species richness and novelty on the south‐western continental slope (∼100–1100 m depth; ∼18° S–35° S). A total of 1979 morphologically defined species was discriminated in seven taxa across all samples: Demospongiae, Decapoda, corals (Octocorallia and Antipatharia), Mollusca, Echinodermata, Ascidiacea, and Pycnogonida. Collectively, 59% were estimated to be new or unnamed species. The distribution pattern of megafaunal communities, analysed with a suite of 17 physical covariates, was most influenced at large spatial scales (>100s km) by bottom temperature, oxygen concentration and latitude, whereas at smaller scales (10s of km), seabed type was most influential. Many covariates are driven by the same physical processes and are correlated (e.g. to depth or latitude), thus it is not possible to ascribe causal relationships to fauna distributions. However, their identification highlights the spatial scales that determine the composition of megafaunal communities. Regional‐scale transitions in bottom temperature and oxygen concentration are determined by water masses and currents that interact with the south‐western margin seabed in different ways depending on location. The nested, smaller‐scale heterogeneity of seabed type, classified simply as ‘hard’ or ‘soft’ terrain, differentiates consolidated attachment sites for sessile fauna from sediments suited to mobile and burrowing fauna. Different physical factors affect the distribution of benthic fauna at different scales. Collectively, these patterns of heterogeneity can be represented in a hierarchical framework that consists of biogeographic provinces, biomes, biogeomorphic features, terrains, and finer scales. The Australian government is using a hierarchical approach to identify bioregions for management purposes; a key aim is to ensure that a National Representative System of Marine Protected Areas (NRSMPA) will meet the requirement of comprehensiveness, adequacy and representativeness. Important findings from this study are that the provincial structure of invertebrate megabenthos broadly aligns with the provincial structure derived earlier from the distribution of fishes, but there are differences in the distribution of individual major taxa at both provincial and megahabitat scales. Representative coverage of rarer taxa or narrowly distributed taxa might not be feasible at the same time as ensuring main fauna groups are adequately represented. The hierarchical scales of heterogeneity of the megabenthos in this area, the differences between taxa, and the high proportion of apparently rare species make it clear that it will be as important to manage the area outside the NRSMPA as to manage the NRSMPA itself. Management will be required at different scales that correspond to the multiscale spatial heterogeneity of continental margin fauna.

Assemblage turnover and taxonomic sufficiency of subtidal macroalgae at multiple spatial scales

Spatial variability in the structure of subtidal macroalgal assemblages in southwest Australia was examined at multiple spatial scales using a three-factor hierarchal design. Spatial extents ranged from metres (between quadrats) to many hundreds of kilometres (between regions), and the study encompassed > 2000 km of temperate coastline. In addition, the influence of taxonomic resolution, from species level data to class level, on spatial patterns was investigated to assess the potential evolutionary timescales of the pattern and for developing cost effective regionally applicable surrogates for biodiversity monitoring. Almost 300 species were identified from 14 sites, representing considerable biodiversity and a significant subset of the total benthic macroalgal diversity in the region (∼ 1000 species). Multivariate variability was significant at all spatial scales examined, but most prominent at smallest spatial scales, regardless of taxonomic resolution. Assemblage and species turnover was pronounced at scales of metres to hundreds of metres. Generally, small scale patchiness was a ubiquitous pattern for all individual taxa examined, regardless of taxonomic resolution, while variability at the scale of 10s of km was less important. Even so, differences in spatial variability between taxa were observed, and ecological and historical reasons for such differences are proposed. Taxonomic aggregation to family level had minimal effect on spatial patterns, but aggregation to order level led to changes in some aspects of patterns of assemblage structure. The unique and speciose macroalgal assemblages on subtidal reefs in southwest Australia are shaped by a complex array of historical and contemporary processes that act at multiple spatial (and temporal) scales. Understanding the relative importance of these processes requires that further manipulative and correlative work is conducted across a range of ecologically-important spatial scales.

Colour patterns in the sea urchin, Heliocidaris erythrogramma, suggest limited connectivity across the Southern and Pacific Ocean coastlines of Australia

Heliocidaris erythrogramma is a widespread Australian sea urchin whose colour varies greatly. Here we report large-scale, hierarchically structured surveys, testing for patterns in colouration of H. erythrogramma associated with wave exposure, and consistency between populations from the Pacific and Southern Oceans. Along the Southern Ocean coastline, more urchins with white dermis were found in (ocean swell-exposed) open coast regions, whereas more urchins with red dermis were usually found in the (ocean swell-protected) bay regions. In contrast, only red dermis urchins were found in both open coast and bay regions along the Pacific coastline. Spine colour was found to be independent of test colour within locations and, while no differences in the frequencies of spine colours were detected between regions of different wave exposure, differences were detected across 1–100s of km within coastlines. Large differences in the frequencies of spine colours were also detected between the two coastlines. Clear differences in two independent characteristics of colour between Southern Ocean and Pacific coastlines, combined with intermediate patterns at a location near the junction of these coastlines, suggest that large-scale morphological patterns might reflect intra-specific genetic differentiation within H. erythrogramma, large-scale environmental differences between temperate Australian coastlines, or an interaction between these two factors.

Multi‐scale recruitment patterns and effects on local population size of a temperate reef fish

Recruitment of the temperate reef fish Coris julis was studied across the Azores Archipelago (central North Atlantic), over four consecutive recruitment seasons and at three spatial scales: between islands (separated by 100s of km), sites within islands (separated by 10s of km) and transects within sites (separated by 10s of m). At the largest scale (i.e. between islands) spatial recruitment patterns were highly variable, suggesting the influence of stochastic processes. Recruitment was spatially consistent within islands, even though magnitude was unpredictable between years, indicating that processes at meso-scales are probably more deterministic. Recruits settled randomly at the transect scale, probably reflecting habitat homogeneity. It was proposed that large and island-scale patterns reflect larval availability, driven by physical and biological processes occurring in the plankton. No evidence was found for a density-dependent relationship between newly settled and 2 week settled C. julis nor between cumulative recruitment and young-of-the-year. It appears that adult density is limited by larval supply (pre-settlement regulation) at low recruitment sites, and determined by post-settlement, density-dependent processes at high recruitment sites. This work is one of few to investigate multiple spatial and temporal scales of recruitment for a coastal fish species inhabiting isolated, temperate oceanic islands and hence, provides a novel comparison to the many studies of recruitment on coral reefs and other, more connected systems.

Asymmetric wear behavior of self-mated copper fiber brush and slip-ring sliding electrical contacts in a humid carbon dioxide environment

This study examines wear phenomenon occurring in high-current density self-mated metal copper sliding contacts in humid carbon dioxide environments. A custom tribometer built to test macroscopic (lightly loaded) brush and slip-ring sliding electrical contacts at relatively high speed and current density is described in the text. Data is presented as further evidence that at some elevated current density (between 120 and 180A/cm2) there is a transition in the wear mechanism as the brush wear rates, friction coefficients, and contact resistances bifurcate. In situ white light interferometry provides new insight on the evolution of slip-ring surfaces as a function of current flow direction through the contact. Ex situ SEM of the brush fiber bundle surfaces shows a strong dissimilitude in the wear of contacting fibers as a result of the current flow direction. Steady-state friction coefficients in the range of 0.20–0.25, linear wear rates of 3–5×10−11m/m, and contact resistances of 0.6mΩ are reported for copper fiber brushes in water saturated carbon dioxide environments at 2.5m/s sliding speed and up to 120A/cm2. A bifurcation occurs at 180A/cm2 where the electron receiving brush (positive bias) exhibits an increase in friction coefficient to a range of 0.3–0.4, and the electron donating brush (negative bias) a drop to 0.18. The positive brush also exhibits an increase in wear rate to 2.3×10−10m/m and a sharp decrease in contact resistance to 0.2mΩ. The negative brush shows an increase in wear rate but only to half the value of the positive brush, and the negative brush contact resistance increased sharply to 0.6–0.8mΩ. An uncertainty analysis of wear rate is presented that demonstrates the need for long (100s of km) sliding distances to achieve a reasonable measurement uncertainty for such low wear contacts.

PROBING FINE-SCALE IONOSPHERIC STRUCTURE WITH THE VERY LARGE ARRAY RADIO TELESCOPE

High resolution (~1 arcminute) astronomical imaging at low frequency (below 150 MHz) has only recently become practical with the development of new calibration algorithms for removing ionospheric distortions. In addition to opening a new window in observational astronomy, the process of calibrating the ionospheric distortions also probes ionospheric structure in an unprecedented way. Here we explore one aspect of this new type of ionospheric measurement, the differential refraction of celestial source pairs as a function of their angular separation. This measurement probes variations in the spatial gradient of the line-of-sight total electron content (TEC) to 0.001 TECU/km accuracy over spatial scales of under 10 km to over 100 km. We use data from the VLA Low-frequency Sky Survey (VLSS; Cohen et al. 2007, AJ 134, 1245), a nearly complete 74 MHz survey of the entire sky visible to the Very Large Array (VLA) telescope in Socorro, New Mexico. These data comprise over 500 hours of observations, all calibrated in a standard way. While ionospheric spatial structure varies greatly from one observation to the next, when analyzed over hundreds of hours, statistical patterns become apparent. We present a detailed characterization of how the median differential refraction depends on source pair separation, elevation and time of day. We find that elevation effects are large, but geometrically predictable and can be "removed" analytically using a "thin-shell" model of the ionosphere. We find significantly greater ionospheric spatial variations during the day than at night. These diurnal variations appear to affect the larger angular scales to a greater degree indicating that they come from disturbances on relatively larger spatial scales (100s of km, rather than 10s of km).

Some like it cold: populations of the tellinid bivalve Macoma balthica (L.) suffer in various ways from a warming climate

Because of its relatively low tolerance to elevated temperatures, Macoma balthica (L.) may be one of the first important marine species in temperate coastal areas to suffer from a warming climate. For the last few decades, the abundance of the species in the Dutch Wadden Sea has been se- riously declining. At lower latitudes, the southern edge of its range recently shifted several 100s of km to the north. To understand changes in abundance related to high temperatures, we studied short-term population responses to warmer than average seasons using data from a long-term (>35 yr) sampling program in the western Wadden Sea. The observed relationships included reduction of reproductive output and recruitment in years starting with mild winter-spring periods, reduction of adult survival in years with warm summers, reduction of annual migration in ~8 mo olds to more favourable areas in mild winters, reduction of growth rates in warmer than average growing seasons, and enhancement of seasonal weight loss in milder than average winters. We conclude that elevated temperatures nega- tively affect population dynamics of M. balthica in a number of ways, i.e. via recruitment or mortality as well as growth. These negative influences were observed already far below the upper lethal tem- perature of the species and in populations living ~1000 km poleward of the warm edge of the species' range. The outcome of M. balthica's energy balance appears to be decisive for their continued exis- tence by effects not only on individual weights but also on mortality as well as reproduction.

The use of taxonomic distinctness indices in assessing patterns of biodiversity in modular organisms

AbstractEstimating diversity of modular organisms may be problematic due to actual difficulties in discriminating between ‘individuals’ and quantifying their abundances. Quantitative data, when available, are collected through methods that could preclude the application of classical diversity indices, making comparisons among studies difficult. Taxonomic distinctness indices, such as the ‘Average Taxonomic Distinctness’ (Δ+) and the ‘Variation in Taxonomic Distinctness’ (Λ+) may represent suitable tools in investigating diversity beyond the simple species number. The potential usefulness of such indices has been explored almost exclusively on unitary organisms, neglecting modular ones. In this study, we employed Δ+ and Λ+ to analyse patterns of diversity of epiphytic hydroid assemblages living on Cystoseira seaweeds at a hierarchy of spatial scales, along 800 km of rocky coast (SE Italy). ANOVA on species richness and Λ+ showed no significant difference in sample diversity at the investigated spatial scales. In contrast, there were significant differences at the scale of 10s of km in Δ+. Analyses based on simulations detected significant variations at all spatial scales in Δ+. Such findings underline the potential of Δ+ in highlighting relevant spatial scales of variation in patterns of hydroid diversity. Our results also suggest that the interplay between natural environmental variations and the complex ecological traits of modular organisms might affect taxonomic distinctness indices. We stress the need for further investigations focusing on modular organisms before any generalizations on the use of taxonomic relatedness measures in examining marine biodiversity can be made.

Patterns in reproductive dynamics of burrowing ghost shrimp Trypaea australiensis from small to intermediate scales

Many studies have examined latitudinal differences in reproduction of marine invertebrates, but few have measured variation at small to intermediate scales (kilometres to hundreds of kilometres), which may confound comparisons across broader geographic regions. Here, we examined variation in the reproductive biology of a little-studied species of burrowing ghost shrimp (Trypaea australiensis) at spatial scales ranging from km (between sites within estuaries) to 100s of km (among estuaries), over a 2-year period in south-eastern Australia. Sex ratios of populations were consistently biased towards females through time and space. Although reproduction started in summer months across all spatial scales, there was a pattern of earlier spawning from southern to northern estuaries. Integration of results from previous studies of T. australiensis supported a similar pattern of earlier breeding from high to low latitudes. Fecundity of shrimp increased linearly with female size, but the relationship varied inconsistently across the different spatial scales. Similarly, sizes at maturity varied from small to intermediate scales and observed patterns were not consistent with general predictions e.g. shrimp were smaller and ovigerous at smaller sizes at sites in the southern-most estuary, compared to estuaries further north. We found no differences in the sizes of embryos across the different spatial scales, but confirm that T. australiensis employs a strategy of high fecundity and small embryo size compared to other thalassinidean shrimp. Our results suggest that factors at smaller scales (e.g. food availability) may be important in affecting reproductive dynamics of T. australiensis, but further research is needed in testing hypotheses about patterns observed here. A lack of similar studies on other marine organisms remains an impediment to understanding life-history strategies and the sustainable management and conservation of populations.

Dispersal and gene flow in the habitat-forming kelp, Ecklonia radiata: relative degrees of isolation across an east - west coastline

Characterising patterns of dispersal and gene flow in habitat-forming organisms is becoming a focal concern for conservation and management strategies as anthropogenic impacts drive change in coastal ecosystems. Here, we use six microsatellite markers to characterise dispersal and gene flow across the South Australian distribution of the habitat-forming kelp Ecklonia radiata. Populations of E. radiata on subtidal reefs in South Australia were highly genetically structured on large (100s of km, FST = 0.211) and small (10s of km, FST = 0.042) spatial scales with the extent of differentiation positively correlated with geographic distances among populations. Neither the presence of oceanic currents nor intervening rocky reef habitats appeared to facilitate widespread gene flow. There was a trend for island populations to be more genetically differentiated from those on the mainland and to have slightly greater levels of heterozygosity than mainland populations. Our results show relatively low dispersal and gene flow suggesting that recovery following kelp loss may be slow. Such information not only provides insights into relative rates of recovery, but may also identify which populations may be best used for propagation and restoration efforts.

Depth profiles of venusian sinuous rilles and valley networks

More than 200 venusian channels and valleys have been mapped based on analyses of Magellan SAR images. Sinuous rilles are the most abundant channels among six types of venusian channels, and they are widely distributed on Venus. Morphological characteristics of venusian sinuous rilles include sinuous narrowing reaches, source depressions, and length of several 10s to a few 100s of km. This type of channels is known to exist on the Moon and possibly on Mars. Valley networks on Venus often occur in the vicinity of or in connection to sinuous rilles. Cross-sectional morphologies of sinuous rilles and valley networks are of special importance in discussing their formation processes both qualitatively and quantitatively. We reconstructed cross-sectional profiles of 6 sinuous rilles and 2 valley networks using a new radar clinometric method. Reconstructed cross-sections revealed that floors of the channels and valleys are clearly lower than the surrounding plains. This finding implies that the sinuous rilles and the valley networks have erosional origins. Longitudinal depth profiles of the sinuous rilles show distinct decreasing trends toward the termini. Such decreasing trends of depths are qualitatively in agreement with theoretical models and laboratory experiments of thermal erosion. In order to verify this assertion quantitatively, we conduct simple 1-dimensional model calculations under the assumption that both channel-forming lavas and ground substrate are tholeiitic basalt. For initial lava thicknesses in the range 2–6 m, the model calculations yield good matches to the depth profiles. Estimated duration of lava effusion ranges from several months to a few years. These numerical results support thermal erosion of the sinuous rilles but do not necessarily exclude contributions from mechanical erosion processes. Valley networks seem to have formed under a strong structural control in comparison to sinuous rilles. The valleys vary widely in characteristics of the depth profile and flow directions relative to surface slopes. Therefore valley networks appear to have originated from diverse formation mechanisms.

Community structure of marine bacterioplankton: patterns, networks, and relationships to function

Major challenges in marine microbial ecology include determining patterns of commu- nity structure and structure-function relationships. Progress has occurred by a combination of mole- cular and classical techniques. An example for this is work on the marine Crenarchaeota, extremely abundant organisms that we now think play important roles both as autotrophic ammonium oxidiz- ers and as heterotrophs. Another involves the recently discovered Proteorhodopsins, pigments that are potentially important in solar energy capture, yet often do not seem to confer a clear growth benefit to organisms that possess them. Proteorhodopsins occur in numerous phylogenetic groups and may have multiple roles, complicating the linking of these proteins to a well-defined function. Community fingerprinting is a powerful tool for examining community structure and for examining spatial and temporal distribution patterns. Using fingerprinting, we found that ocean communities tend to occur in patches with horizontal dimensions of several km, while samples 10s of km or more apart can be quite different. Temporal analyses such as the San Pedro Ocean Time Series (SPOT) show that near-surface communities are somewhat similar from month to month, then change signif- icantly over several months, and finally return to a similar community annually. Near-surface com- munities can also be predicted from environmental parameters like temperature, salinity, nutrients, and chlorophyll. Time series data show co-occurrence of organisms (resembling a succession of com- munities) under particular conditions, or conversely can show which organisms are significantly neg- atively correlated, indicative perhaps of competition, resource partitioning, or allelopathy. These relationships are visualized here as mathematical interaction networks to map out the 'niche space' of microbial taxa and their correlations, displaying complex ecological interactions. Observations indicate that ecological relatedness does not necessarily closely follow phylogenetic relatedness.

Oceanic core complexes and ancient oceanic lithosphere: Insights from Iapetan and Tethyan ophiolites (Canada and Albania)

Oceanic ridges are extensional environments characterized by brittle to ductile normal faulting and episodic magma supply. Studies in modern oceanic settings suggest that the interplay of low-angle detachments and high-angle normal faults locally lead to the exhumation of lower crust and upper mantle peridotites to the seafloor as oceanic core complexes. Along the Mid-Atlantic ridge, core complexes typically occur in inside corners of intersections between the ridge axis and major transform faults. The core complexes were exhumed by movement along long-lived detachment faults that extend for 10s of km, and that are crosscut by high-angle normal faults oriented parallel to the rift axis. Ridge segments with abundant detachments would be characterized by lithosphere having little or no upper crust. Similar features in ophiolites may also reflect the dominance of amagmatic extension. This contribution presents two examples of fossilized oceanic core complexes preserved in the Canadian Appalachian and Albanian Dinaride ophiolite belts. In the Canadian Appalachians, the Southern Quebec ophiolites experienced two Paleozoic orogenies after their obduction onto the Laurentian margin. Although locally obscured by tectonic fabrics and structures, the original relationships between the ophiolitic mantle, the overlying plutonic section, and onlapping Ordovician siliciclastic rocks are well-preserved in the Thetford-Mines ophiolite which also shows similarities with lithological and structural features of the Mirdita ophiolite, where conformable contacts between the sedimentary cover sequence (debris flows and flysch deposits) and the mantle and crustal sections are superbly exposed. The Jurassic Mirdita ophiolite in Albania underlies ca. 4000 km 2 and was only slightly affected by the Tertiary Alpine orogeny of Eastern Europe. Well-exposed sections of the ophiolite suggest that the oceanic mantle was exhumed prior to obduction and locally records the formation of an oceanic core complex. Mafic cumulates of the Mirdita ophiolite have been totally excised in places, and exhumation-related shear zones are preserved in the Krabbi–Puka massif. The shear zones are manifested both within the mantle and at the contact with overlying basalts. The ophiolitic sedimentary sequence was deposited on basalts, sheeted dykes or gabbros, and typically consists of debris flows intercalated with, and overlain by slumped oceanic sedimentary rocks. The lithological and structural characteristics of both the Thetford-Mines and the Mirdita ophiolites are consistent with extensional tectonism, crustal excision and lower crust/upper mantle exhumation during formation. Both ophiolites are believed to have originated during asymmetrical oceanic extension in a suprasubduction zone setting, with preservation of the upper-plate/lower-plate segments during obduction.