Demersal fish assemblages off southern New Zealand in relation to depth and temperature

We examined the relationship between demersal fish assemblage and depth, temperature, latitude and longitude off southern New Zealand (46–54°S and 165–180°E) in water depths of 80–787 m. Catch weight data were analysed by two-way indicator analysis (TWIA), groupaverage agglomerative clustering (UPGMA) and Detrended Correspondence Analysis (DCA). The spatial pattern of demersal fish off southern New Zealand conforms to the concept of species groups or fish assemblages related to environmental gradients. Shallow-water assemblages were dominated by species from the families Gempylidae, Squalidae, Triakidae and Moridae, mainly represented by Thyrsites atun, Squalus acanthias, Galeorhinus australis, and Pseudophycis bachus. Deep water assemblages were dominated by Chimaeridae, Argentinidae, Merlucciidae and Macrouridae, mainly represented by Hydrolagus novaezelandiae, Argentina elongata, Macruronus novaezelandiae, and Lepidorhynchus denticulatus. Total catch weight was often dominated by Merlucciidae, Macrouridae and Gempylidae. Fish assemblages were related to discrete ranges of depth (< and >300 m) and temperature (< and >9.5°C), but the range of sediment types was too narrow to show any correlation.     

Murky water: Analyzing risk perception and stakeholder vulnerability related to sewage impacts in mangroves of East Africa

Coastal cities in East Africa are growing rapidly and consequently there is a rapid increase in urban sewage production, putting added pressure on already strained treatment systems. As a result, peri-urban mangroves are receiving extensive amounts of sewage but very little is know as to the ecological and societal consequences of this. However, UNEP among others advocate the use of low-cost, natural sewage treatment technology whenever possible and mangroves have been suggested as useful second stage biofilters. Because of the high resource dependency in many peri-urban coastal communities in East Africa, it is imperative to investigate potential societal impacts on local communities using sewage impacted peri-urban mangroves. Consequently this paper aims to characterize stakeholder groups currently affected by sewage impacted mangroves and thus also map vulnerabilities across local users in relation to future initiatives to use mangroves as biofilters along the East African coast. As risk perception is an important part of vulnerability, and risk perception related to sewage and pollution in an African setting has been little studied, we also aim to contribute baseline data on risk perception related to pollution across peri-urban populations in Kenya, Tanzania and Mozambique.     

A new determination of the orbit and masses of the Be binary system δ Scorpii

The binary star δ Sco (HD143275) underwent remarkable brightening in the visible in 2000, and continues to be irregularly variable. The system was observed with the Sydney University Stellar Interferometer (SUSI) in 1999, 2000, 2001, 2006 and 2007. The 1999 observations were consistent with predictions based on the previously published orbital elements. The subsequent observations can only be explained by assuming that an optically bright emission region with an angular size of  ≳2 ± 1 mas  formed around the primary in 2000. By 2006/2007 the size of this region grew to an estimated ≳4 mas.
We have determined a consistent set of orbital elements by simultaneously fitting all the published interferometric and spectroscopic data as well as the SUSI data reported here. The resulting elements and the brightness ratio for the system measured prior to the outburst in 2000 have been used to estimate the masses of the components. We find   M_A = 15 ± 7 M_⊙  and   M_B = 8.0 ± 3.6 M_⊙  . The dynamical parallax is estimated to be  7.03 ± 0.15 mas  , which is in good agreement with the revised Hipparcos parallax.     

Mercury Dynamics in a San Francisco Estuary Tidal Wetland: Assessing Dynamics Using In Situ Measurements

We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM??representative of particle-associated and filter-passing Hg, respectively??together predicted 94?% of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, 2005?C2006. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particle-associated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes.     

Is Ocean Acidification an Open-Ocean Syndrome? Understanding Anthropogenic Impacts on Seawater pH

Ocean acidification due to anthropogenic CO₂ emissions is a dominant driver of long-term changes in pH in the open ocean, raising concern for the future of calcifying organisms, many of which are present in coastal habitats. However, changes in pH in coastal ecosystems result from a multitude of drivers, including impacts from watershed processes, nutrient inputs, and changes in ecosystem structure and metabolism. Interaction between ocean acidification due to anthropogenic CO₂ emissions and the dynamic regional to local drivers of coastal ecosystems have resulted in complex regulation of pH in coastal waters. Changes in the watershed can, for example, lead to changes in alkalinity and CO₂ fluxes that, together with metabolic processes and oceanic dynamics, yield high-magnitude decadal changes of up to 0.5 units in coastal pH. Metabolism results in strong diel to seasonal fluctuations in pH, with characteristic ranges of 0.3 pH units, with metabolically intense habitats exceeding this range on a daily basis. The intense variability and multiple, complex controls on pH implies that the concept of ocean acidification due to anthropogenic CO₂ emissions cannot be transposed to coastal ecosystems directly. Furthermore, in coastal ecosystems, the detection of trends towards acidification is not trivial and the attribution of these changes to anthropogenic CO₂ emissions is even more problematic. Coastal ecosystems may show acidification or basification, depending on the balance between the invasion of coastal waters by anthropogenic CO₂, watershed export of alkalinity, organic matter and CO₂, and changes in the balance between primary production, respiration and calcification rates in response to changes in nutrient inputs and losses of ecosystem components. Hence, we contend that ocean acidification from anthropogenic CO₂ is largely an open-ocean syndrome and that a concept of anthropogenic impacts on marine pH, which is applicable across the entire ocean, from coastal to open-ocean environments, provides a superior framework to consider the multiple components of the anthropogenic perturbation of marine pH trajectories. The concept of anthropogenic impacts on seawater pH acknowledges that a regional focus is necessary to predict future trajectories in the pH of coastal waters and points at opportunities to manage these trajectories locally to conserve coastal organisms vulnerable to ocean acidification.     

Evidence for Archean ocean crust with low high field strength element signature from diamondiferous eclogite xenoliths

Late Archean (2.57 Ga) diamond-bearing eclogite xenoliths from Udachnaya, Siberia, exhibit geochemical characteristics including variation in oxygen isotope values, and correlations of δ¹⁸O with major elements and radiogenic isotopes which can be explained by an origin as subducted oceanic crust. Trace element analyses of constituent garnet and clinopyroxene by Laser-ICPMS are used to reconstruct whole-rock trace element compositions, which indicate that the eclogites have very low high field strength element (HFSE) concentrations and Zr/Hf and Nb/Ta ratios most similar to modern island arcs or ultradepleted mantle. Although hydrothermal alteration on the Archean sea floor had enough geochemical effect to allow the recognition of its effects in the eclogites and thus diagnose them as former oceanic crust, it was not severe enough to erase many other geochemical features of the original igneous rocks, particularly the relatively immobile HFSEs. Correlations of the trace element patterns with oxygen isotopes show that some, generally Mg-richer, eclogites originated as lavas, whereas others have lower δ¹⁸O and higher Sr and Eu contents indicating an origin as plagioclase-bearing intrusive rocks formed in magma chambers within the ocean crust. Major and trace element correlations demonstrate that the eclogites are residues after partial melting during the subduction process, and that their present compositions were enriched in MgO by this process. The original lava compositions were picritic, but not komatiitic, whereas the intrusives had lower, basaltic MgO contents. The HFSE signature of the eclogites may indicate that ocean floor basalts of the time were relatively close to island arcs and recycled material, which would be consistent with a larger number of smaller oceanic plates. Their composition appears to indicate that komatiitic ocean crust compositions were restricted to the early Archean which is not known to be represented among the eclogite xenolith population.     

Are all patterns created equal? Cooperation is more likely in spatially simple habitats

Cooperative behaviours, such as aggregation with neighbouring conspecifics, can enhance resilience in habitats where risks (i.e. predation, physical disturbances) are high, exerting positive feedback loops to maintain a healthy population. At the same time, cooperation behaviours can involve some extra energy expenditures and increasing resource competition. For sessile reefs, like mussels, simulation models predict increased cooperation under increasing levels of environmental stress. Predation risk is viewed as a behaviour‐modifying stressor, but its role on cooperation mechanisms, such as likelihood of reciprocity, has not yet been empirically tested. This study harnesses this framework to understand how cooperation changes under different perceived levels of predation risk, using mussel beds as model of a complex “self‐organised” system. Hence, we assessed the context dependency of cooperation response in different “landscapes of fear,” created by changes in predator cues, substratum availability and body size. Our experiments demonstrated that i) cooperation in a mussel bed system increases when predator cues are present, but that this relationship was found to be both, ii) strongly context‐dependent, particularly upon substratum availability and iii) size‐dependent. That is, while cooperation is in general greater for larger individuals, the response to risk results in greater cooperation when alternative attachment substratum is absent, meaning that simpler landscapes may be perceived as riskier. The context dependency of structural complexity is also an essential finding to consider in a changing world where habitats are losing complexity and cooperative strategies should be maximised.     

Productivity cycles in the coastal upwelling area off Concepción: The importance of diatoms and bacterioplankton in the organic carbon flux

Recurrent coastal upwelling is recognized as one of the main factors promoting the exceptionally high productivity of the Humboldt Current System. Herein, we study time series data of gross primary production (2003-2006) and its fluctuation in relation to seasonal changes in the light and nutrient field of the Concepción upwelling ecosystem. Concurrent measurements of gross primary production, community respiration, bacterial secondary production, and sedimentation rates allowed a characterization of the main carbon fluxes and pathways in the study area. The integrated values of gross primary production were higher during the upwelling period (>1 g C m⁻² d⁻¹; October-April; that is, early spring to early austral fall). Seasonal changes in the system were also reflected in community respiration, organic matter sedimentation, and bacterial production rates, which varied along with the gross primary production. The significant correlation between gross primary production and community respiration (Spearman, r = 0.7; p < 0.05; n = 18) reflected an important degree of coupling between organic matter formation and its usage by the microplanktonic community during periods when gross primary production/community respiration were highly similar. Higher gross primary production values (>6 g C m⁻² d⁻¹) were consistently associated with maximum biomass levels of Skeletonema costatum and Thalassiosira subtilis. We observed a positive correlation between gross primary production and the sedimentation of intact diatom cells (Spearman, r = 0.5, p < 0.05, n = 17). Our data suggest that, in the Concepción upwelling ecosystem, bacteria utilize an important fraction of the gross primary production. If our interpretations are correct, they leave unanswered the question of how the system supports the extremely high fish biomass levels, therein pointing out the system’s limited capacity to buffer the evasion of CO₂ following upwelling.     

Plume and lithologic profiling with surface resistivity and seismic tomography

Improved surface-based geophysical technologies that are commercially available provide a new level of detail that can be used to guide ground water remediation. Surface-based multielectrode resistivity methods and tomographic seismic refraction techniques were used to image to a depth of approximately 30 m below the surface at the Natural and Accelerated Bioremediation Research Field Research Center. The U.S. Department of Energy (DOE) established the research center on the DOE Oak Ridge Reservation in Oak Ridge, Tennessee, to conduct in situ field-scale studies on bioremediation of metals and radionuclides. Bioremediation studies are being conducted on the saprolite, shale bedrock, and ground water at the site that have been contaminated with nitrate, uranium, technetium, tetrachloroethylene, and other contaminants (U.S. DOE 1997). Geophysical methods were effective in imaging the high-ionic strength plume and in defining the transition zone between saprolite and bedrock zones that appears to have a significant influence on contaminant transport. The geophysical data were used to help select the location and depth of investigation for field research plots. Drilling, borehole geophysics, and ground water sampling were used to verify the surface geophysical studies.