Habitat use patterns of the invasive red lionfish Pterois volitans: a comparison between mangrove and reef systems in San Salvador,Bahamas

The Indo‐Pacific red lionfish Pterois volitans is widespread both in its native and its non‐native habitats. The rapid invasion of this top predator has had a marked negative effect on fish populations in the Western Atlantic and the Caribbean. It is now well documented that lionfish are invading many tropical and sub‐tropical habitats. However, there are fewer data available on the change in lionfish abundance over time and the variation of body size and diet across habitats. A recent study in San Salvador, Bahamas, found body size differences between individuals from mangrove and reef systems. That study further suggested that ontogenetic investigation of habitat use patterns could help clarify whether lionfish are using the mangrove areas of San Salvador as nurseries. The aim of the present study is to determine temporal trends in lionfish relative abundance in mangrove and reef systems in San Salvador, and to further assess whether there is evidence suggesting an ontogenetic shift from mangroves to reef areas. Accordingly, we collected lionfish from mangrove and reef habitats and calculated catch per unit effort (a proxy for relative abundance), compared body size distributions across these two systems, and employed a combination of stable isotope, stomach content, and genetic analyses of prey, to evaluate differences in lionfish trophic interactions and habitat use patterns. Our results show that populations may have increased in San Salvador during the last 4 years, and that there is a strong similarity in body size between habitats, stark differences in prey items, and no apparent overlap in the use of habitat and/or food resources. These results suggest that there is not evidence an for ontogenetic shift from mangroves to reefs, and support other studies that propose lionfish are opportunistic forages with little movement across habitats.     

Intraguild predation and partial consumption of blue sharks Prionace glauca by Cape fur seals Arctocephalus pusillus pusillus

The top-down effects of predators on ecosystem structure and dynamics have been studied increasingly. However, the nature and consequence of trophic interactions between upper-trophic-level predators have received considerably less attention. This is especially the case in marine systems due to the inherent challenges of studying highly mobile marine species. Here we describe the first documentation of asymmetrical intraguild predation by a pinniped predator on a mid-sized predatory shark. The report is based on direct observations in South African waters, in which free-swimming blue sharks Prionace glauca were captured and partially consumed by Cape fur seals Arctocephalus pusillus pusillus. These observations are important not just for understanding the interactions between these two species but more broadly for their implications in understanding the trophic ecology of pinnipeds, many populations of which have increased while numerous shark populations have declined.     

Kelp gulls prey on the eyes of juvenile Cape fur seals in Namibia

The kelp gull Larus dominicanus is an abundant and highly successful avian predator and scavenger that breeds along the coastline in the Southern Hemisphere, ranging from Antarctica to the tropics. On account of its dietary breadth, wide-ranging foraging strategies, and acclimation to modified landscapes, this species has received considerable attention within the seabird literature over the past 40 years. Furthermore, owing to its ready habituation to human-dominated environments, the species has been used as a bio-indicator of habitat modification. Here we describe new predatory behaviours of the kelp gull on a larger-bodied sympatric mammal species, the Cape fur seal Arctocephalus pusillus pusillus, along the coast of Namibia, and discuss our findings as they relate to food web dynamics and behavioural plasticity.     

缅甸硬玉岩中的流体包裹体

缅甸硬玉岩是世界上最大和最重要的玉石矿床之一,位于印度板块和欧亚板块之间的新特提斯洋缝合带中。研究表明,缅甸硬玉岩是新特提斯洋壳俯冲过程中橄榄岩经高压变质、交代作用形成的。对不同变质程度缅甸硬玉岩样品中的流体包裹体的研究表明,缅甸硬玉岩中含有4种类型的流体包裹体:1不含或含少量甲烷的低盐度水溶液包裹体(Ⅰ型),呈孤立状或小群(簇状)产于硬玉晶体核部,或沿着硬玉晶体的生长环带分布,具有原生生长结构;2含石盐子晶的H2O+Na Cl±CH4三相包裹体(Ⅱ型);3纯甲烷(CH4)包裹体(Ⅲ型),可以细分为高密度(Ⅲa)和低密度(Ⅲb)两种;4气相或空包裹体(Ⅳ型)。研究表明,缅甸硬玉岩及其相关岩石在形成和演化过程中发生了多期次流体交代事件。硬玉形成过程中,交代橄榄岩的流体相可能来自海水。首次在缅甸硬玉岩中识别出高盐度的含水包裹体和高密度的含CH4包裹体。高盐度的含水包裹体可能与硬玉岩重结晶过程相关,而高密度的CH4流体可能为俯冲板片的上地幔楔中超基性岩蛇纹石化过程的副产物。计算的流体包裹体等容线表明,硬玉岩演化过程中这些流体包裹体发生了不同程度的再平衡。     

Field assessment of surface water–groundwater connectivity in a semi‐arid river basin (Murray–Darling,Australia)

In semi‐arid and arid river basins, understanding the connectivity between rivers and alluvial aquifers is one of the key challenges for the management of groundwater resources. The type of connection present (gaining, losing‐connected, transitional and losing‐disconnected) was assessed at 12 sites along six Murray–Darling Basin river reaches. The assessments were made by measuring the hydraulic head in the riparian zone near the rivers to evaluate if the water tables intersected the riverbeds and by measuring fluid pressure (ψ) in the riverbeds. The rationale for the latter was that ψ will always be greater than or equal to zero under connected conditions (either losing or gaining) and always lesser than or equal to zero under losing‐disconnected conditions. A mixture of losing‐disconnected, losing‐connected and gaining conditions was found among the 12 sites. The losing‐disconnected sites all had a riverbed with a lower hydraulic conductivity than the underlying aquifer, usually in the form of a silty clay or clay unit 0.5–2 m in thickness. The riparian water tables were 6 to 25 m below riverbed level at the losing‐disconnected sites but never lower than 1 m below riverbed level at the losing‐connected ones. The contrast in water table depth between connected and disconnected sites was attributed to the conditions at the time of the study, when a severe regional drought had generated a widespread decline in regional water tables. This decline was apparently compensated near losing‐connected rivers by increased infiltration rates, while the decline could not be compensated at the losing‐disconnected rivers because the infiltration rates were already maximal there. Copyright © 2012 John Wiley & Sons, Ltd.     

Snow accumulation and ablation response to changes in forest structure and snow surface albedo after attack by mountain pine beetle

This study quantified changes in snow accumulation and ablation with forest defoliation in a young pine stand attacked by mountain pine beetle, a mature mixed species stand, and a clearcut in south‐central British Columbia. From 2006 to 2012, as trees in the pine stand turned from green to grey, average canopy transmittance increased from 27% to 49%. In the mixed stand, transmittance remained constant at 19%. In 2009, the year of greatest needle loss, average snow surface litter cover in the pine stand was 29% (range 4 – 61%), compared to ≤9% in other years and over double that in the mixed stand. By 2012, litter accumulation in the now‐grey pine stand was only a sixth of that in the mixed stand. Inter‐annual variability in the weather had the greatest effect on snow accumulation and ablation, with the greatest differences between both forested stands and the clearcut occurring in 2010, the year of lowest SWE. Differences in snow accumulation between the pine and mixed stand increased in 2010 as a result of decreased snow interception in the young stand after needlefall. Average ablation rates in the attacked stand were most different from the mixed stand in 2009 and 2012, the years with the largest and smallest over‐winter needle loss, respectively. This study shows that grey, non‐pine, and understory trees moderate snow response to changes in the main canopy. It also highlights the complex interrelationships between ecohydrological processes key to assessing watershed response to forest cover loss in snow dominated hydrologic regimes. Copyright © 2012 John Wiley & Sons, Ltd.     

Unsaturated zone fracture flow contributions to stream flow: evidence for the process in South Africa and its importance

Understanding hydrological processes has always been important to the development and successful application of conceptual hydrological models. It can also contribute to informed water resources management, particularly in the context of understanding the potential impacts of both land use and climate change. Improved conceptual and quantitative understanding of near‐surface hydrological processes emerged through field studies during the 1960s to1980s; however, there remains a degree of ambiguity about the processes that link surface water and groundwater. This is especially the case in South Africa where a great deal of confusion has arisen about the source of the ‘baseflow’ signal in stream flow observations. This paper suggests that fracture flow within the unsaturated zone could have a lateral component and therefore re‐emerge and contribute to stream flow in catchments with relatively steep topography. The implication is that ‘baseflows’ could be made up of groundwater contributions (caused by intersection of the water table with stream channels) as well as an unsaturated zone flow component. Evidence for the existence of the process is presented on the basis of small‐scale observations and interpretations of stream flow observations. The potential importance of the process relates to interpreting different methods of recharge estimation, assessing the impacts of groundwater abstraction on stream flow, as well as the application and interpretation of the results of hydrological models. The conclusions are that the process does exist, but that there is less than conclusive evidence for its importance. There is therefore a need for further studies that can quantify the scale of the process and therefore its importance. Only then will it be possible to develop a consistent understanding of the processes of surface water and groundwater interaction and therefore manage water resources in a truly integrated manner. Copyright © 2009 John Wiley & Sons, Ltd.     

Stream temperature dynamics in two hydrogeomorphically distinct reaches

The objective of this study was to analyse stream temperature variability during summer in relation to both surface heat exchanges and reach‐scale hydrology for two hydrogeomorphically distinct reaches. The study focused on a 1·5‐km wildfire‐disturbed reach of Fishtrap Creek located north of Kamloops, British Columbia. Streamflow measurements and longitudinal surveys of electrical conductivity and water chemistry indicated that the upper 750 m of the study reach was dominated by flow losses. A spring discharged into the stream at 750 m below the upper reach boundary. Below the spring, the stream was neutral to losing on three measurement days, but gained flow on a fourth day that followed a rain event. Continuous stream temperature measurements typically revealed a downstream warming along the upper 750 m of the study reach on summer days, followed by a pronounced cooling associated with the spring, with little downstream change below the spring. Modelled surface energy exchanges were similar over the upper and lower sub‐reaches, and thus cannot explain the differences in longitudinal temperature patterns. Application of a Lagrangian stream temperature model provided reasonably accurate predictions for the upper sub‐reach. For the lower sub‐reach, accurate prediction required specification of concurrent flow losses and gains as a hydrological boundary condition. These findings are consistent with differences in the hydrogeomorphology of the upper and lower sub‐reaches. The modelling exercise indicated that substantial errors in predicted stream temperature can occur by representing stream‐surface exchange as a reach‐averaged one‐directional flux computed from differences in streamflow between the upper and lower reach boundaries. Further research should focus on reliable methods for quantifying spatial variations in reach‐scale hydrology. Copyright © 2010 John Wiley & Sons, Ltd.     

Interactions between groundwater seepage and sediment porewater sulphate concentration profiles in lake anna,Virginia

Most sulphur diagenesis models predict that SO₄^2- concentrations decrease exponentially with increasing sediment depth and are lower than that of the overlying water throughout the sediments. Low SO₄^2- concentrations (less than 0.2 mM) are common in the sediments of Lake Anna that receive acid mine drainage; however, sediment with as much as 20 mM SO₄^2- at about 20cm below the sediment surface is also seen in this section of the lake. A decision tree was proposed to investigate the cause of the high SO₄^2- concentrations at depth (HSD) in the sediment. The first possibility proposed was that an increase in the quantity of groundwater flowing through Lake Anna sediments may increase groundwater advection of SO₄^2- or oxygen which would induce sulphide oxidation. This hypothesis was tested by measuring groundwater flow. HSD profiles were found in a discrete region of the lake; however, stations having these profiles did not have higher groundwater flow than other sites sampled. Alternate explanations for the HSD profiles were that the region in which they occurred had: (1) unusual sediment chemical compositions; (2) a different source of regional groundwater, or (3) a lateral intrusion of high SO₄^2- groundwater. There were no differences in sulphide and organic matter concentrations between the two regions. The area which has HSD in the sediment covers a large area in the middle of the lake, so it is unlikely that it has a unique source of regional groundwater. The third alternative was supported by the fact that in all three sample years, HSD stations were located in the preimpoundment stream channel, which is a likely lateral flow path for groundwater containing high SO₄^2- concentrations.