Parker/buoyancy instabilities with anisotropic thermal conduction, cosmic rays, and arbitrary magnetic field strength

We report the results of a local stability analysis for a magnetized, gravitationally stratified plasma containing cosmic rays. We account for cosmic-ray diffusion and thermal conduction parallel to the magnetic field and allow beta to take any value, where p is the plasma pressure and B is the magnetic field strength. We take the gravitational acceleration to be in the -z-direction and the equilibrium magnetic field to be in the y-direction, and we derive the dispersion relation for small-amplitude instabilities and waves in the large-|k_x| limit. We use the Routh-Hurwitz criterion to show analytically that the necessary and sufficient criterion for stability in this limit is n k_B dT/dz + dp_cr/dz + (1/8pi)dB^2/dz > 0, where T is the temperature, n is the number density of thermal particles, and p_cr is the cosmic-ray pressure. We present approximate analytical solutions for the normal modes in the low- and high-diffusivity limits, show that they are consistent with the derived stability criterion, and compare them to numerical results obtained from the full, unapproximated, dispersion relation. Our results extend earlier analyses of buoyancy instabilities in galaxy-cluster plasmas to the beta <= 1 regime. Our results also extend earlier analyses of the Parker instability to account for anisotropic thermal conduction, and show that the interstellar medium is more unstable to the Parker instability than was predicted by previous studies in which the thermal plasma was treated as adiabatic.Comment: 36 pages, 2 figures, Accepted for publication in Ap

Buoyancy Instabilities in Galaxy Clusters: Convection Due to Adiabatic Cosmic Rays and Anisotropic Thermal Conduction

Using a linear stability analysis and two and three-dimensional nonlinear simulations, we study the physics of buoyancy instabilities in a combined thermal and relativistic (cosmic ray) plasma, motivated by the application to clusters of galaxies. We argue that cosmic ray diffusion is likely to be slow compared to the buoyancy time on large length scales, so that cosmic rays are effectively adiabatic. If the cosmic ray pressure $p_{cr}$ is $\gtrsim 25$ of the thermal pressure, and the cosmic ray entropy ($p_{\rm cr}/\rho^{4/3}$; $\rho$ is the thermal plasma density) decreases outwards, cosmic rays drive an adiabatic convective instability analogous to Schwarzschild convection in stars. Global simulations of galaxy cluster cores show that this instability saturates by reducing the cosmic ray entropy gradient and driving efficient convection and turbulent mixing. At larger radii in cluster cores, the thermal plasma is unstable to the heat flux-driven buoyancy instability (HBI), a convective instability generated by anisotropic thermal conduction and a background conductive heat flux. Cosmic-ray driven convection and the HBI may contribute to redistributing metals produced by Type 1a supernovae in clusters. Our calculations demonstrate that adiabatic simulations of galaxy clusters can artificially suppress the mixing of thermal and relativistic plasma; anisotropic thermal conduction allows more efficient mixing, which may contribute to cosmic rays being distributed throughout the cluster volume.Comment: submitted to ApJ; 15 pages and 12 figures; abstract shortened to < 24 lines; for high resolution movies see http://astro.berkeley.edu/~psharma/clustermovie.htm

Infestation of shore crab gills by a free-living mussel species

Parasitic and commensal species can impact the structure and function of ecological communities and are typically highly specialized to overcome host defences. Here, we report multiple instances of a normally free-living species, the blue mussel Mytilus edulis Linnaeus, 1758, inhabiting the branchial chamber of the shore crab Carcinus maenas (Linnaeus, 1758) collected from widely separated geographical locations. A total of 127 C. maenas were examined from four locations in the English Channel, one location in the Irish Sea and two locations at the entrance of the Baltic Sea. The branchial chambers of three crabs (one from the English Channel and two from Gullmar Fjord, Sweden) were infested with mussels resembling the genus Mytilus. Sequencing at the Me15/16 locus on the polyphenolic adhesive protein gene confirmed the identity as M. edulis. Bivalve infestation always occurred in larger red male individuals. Up to 16 mussels, ranging from 2 to 11 mm in shell length, were found in each individual, either wedged between gill lamellae or attached to the branchial chamber inner wall. This is one of the first reports of a bivalve inhabiting crustacean gills and is an intriguing case of a normally free-living prey species infesting its predato

Decline in growth rate of juvenile European plaice (Pleuronectes platessa) during summer at nursery beaches along the west coast of Scotland

This study concludes that declines in growth rates of young-of-the-year European plaice (Pleuronectes platessa) (YOY plaice) during summer vary spatially and between years and that these dynamics are not driven by temperature, body size, or competition. RNA-predicted growth rates of YOY plaice on the west coast of Scotland declined linearly between mid-July and mid-September, with faster declines at beaches and in years where growth rates were initially high. Absolute growth estimates rarely approached ad libitum laboratory rates, and relative declines in growth rates were unrelated to temperature or body size allometry, indicating that maximum growth was rare. However, the absence of inverse relationships between spatial or temporal growth variation and YOY plaice or brown shrimp (Crangon crangon) densities suggests that competition did not limit growth. There were no consistent trends in morphometric condition factor, biochemical composition, or energy content during summer, indicating that apparent growth declines did not result from energy storage and did not result in depletion of energy stores. Influences of extrinsic factors (such as prey conditions, physical disturbance, and predator densities) on the diet, mediated by behavioral decisions to optimize growth with other ecological constraints, require further investigation as causes of growth variation in YOY plaice

Spatial variation in growth rate of early juvenile European plaice Pleuronectes platessa

Patterns and causes of spatial variation in RNA-predicted growth rates in mid-August were examined in young-of-the-year European plaice Pleuronectes platessa (‘YOY plaice’) at 22 beaches along a 300 km stretch of coastline in west Scotland in 3 consecutive years. According to restricted maximum likelihood models, growth rates varied among beaches (25 km scale), but these spatial patterns were not consistent across years. We found no evidence for spatial variation in growth at the scale of subregions (50 km) or regions (100 km). Growth rate was positively correlated with total length, both within and among beaches and years. In general, YOY plaice in mid-August grew more slowly than estimated ad libitum laboratory rates. Average growth rates by beach and year were inversely related to intraspecific competitor densities, but not interspecific competitor densities (brown shrimp Crangon crangon) or 2 environmental productivity metrics (nearshore chlorophyll a concentration and lugworm Arenicola marina cast density). Physical beach characteristics also explained a significant source of spatial growth variation, with fish growing faster at beaches with larger tidal range and wave fetch. Therefore, the hypothesis of sub-maximum growth due to intraspecific competition (density-dependent growth) was supported, but additional, previously unexplored processes related to physical beach characteristics appear to have important influences on the spatial growth dynamics of YOY plaice

Growth dynamics of European plaice Pleuronectes platessa L. in nursery areas: a review

Young-of-the-year European plaice Pleuronectes platessa L. (hereafter: ‘YOY plaice’) in shallow, sandy areas is a long- and intensively-studied species and an ideal model for understanding growth dynamics in fish nurseries. In order to provide an overview of and access point to this rich literature and to guide future research on juvenile fish growth dynamics, we review patterns of growth variation in YOY plaice following settlement and evaluate evidence for underlying causes, including maximum growth, temperature, prey conditions and competition. A decline in growth rate during late summer and autumn was the clearest and most widespread pattern, but was not clearly related to any of the potential causes previously considered. Interannual growth variation was substantial and despite evidence that intraspecific competition was responsible, other possible causes were also supported and others were only rarely assessed. Growth also varied considerably at a range of spatial scales (100s of m–100s of km). Causes of small-scale (&lt; 10 km) and regional (&gt; 200 km) growth variation remain poorly understood and while intermediate-scale growth variation has been related to prey conditions and intraspecific competition, the role of interspecific competition requires further investigation. Therefore, despite clear evidence for growth heterogeneity at numerous spatiotemporal scales, underlying causes remain elusive. We highlight some principal challenges to measuring and understanding the complex and scale-dependent causes of growth variation. To overcome these challenges, and therefore resolve important nursery processes for juvenile fish, we recommend more detailed and spatiotemporally explicit investigations of growth, metabolic processes and physiological energetics in situ; a focus on possible proximate and ultimate factors driving these dynamics; and development of new hypotheses to explain growth variation starting with general physical features that define nursery environments

Small-scale spatial and temporal heterogeneity in growth and condition of juvenile fish on sandy beaches

To characterize fine-grained heterogeneity in the functional role of sandy beaches as fish nurseries, we measured RNA concentration, DNA concentration and RNA-predicted growth rate in young-of-the-year European plaice Pleuronectes platessa L. (‘YOY plaice’) at beaches on the western side of the British Isles at small alongshore (100–500 m), temporal (days to weeks), depth (0.5–2 m below waterline) and inter-individual scales. We compared variations in these nucleic-acid-based metrics of condition and growth with a null metric (total length) considered to be less responsive to short-term changes in environmental conditions. All four metrics varied at small spatial and temporal scales, particularly RNA-based metrics of short-term condition and growth. A decline in condition and growth during summer was the most important source of temporal variation. Condition and growth also increased with depth below waterline. Alongshore variations within a beach were relatively small, but variance among stations on the same beach (500 m scale) was similar in magnitude to variance among beaches separated by 100 km. High variance in nucleic acid concentrations among samples resulted not only from technical error but also from inter-individual variation. Our application of high-resolution biochemical indices therefore demonstrates that functional roles of sandy beaches can be structured at remarkably small spatial (500 m) and temporal (days) scales, within a single beach

No evidence for impacts to the molecular ecophysiology of ion or CO2 regulation in tissues of selected surface-dwelling bivalves in the vicinity of a sub-seabed CO2 release

Whilst sub-seabed Carbon Capture and Storage (CCS) has the potential to remove a significant proportion of anthropogenic CO2 emissions at source, research is necessary to constrain the environmental impacts of potential future gas leaks from storage reservoirs. The QICS project (Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbons Storage) was established to improve our understanding of these potential impacts and to develop tools and best practice for monitoring sub-seabed CCS reservoirs. Exposure to increased environmental CO2 has been shown to raise the tissue pCO2 of many marine invertebrate species, leading to tissue acidosis and perturbations in both ion transport and bicarbonate buffering. These disturbances can cause downstream effects, seen as metabolic depression in susceptible organisms, compromising the role of particular species within an ecosystem and even causing the local extinction of species groups. To monitor the potential impact to surficial benthic megafauna, cages of bivalves (the common mussel Mytilus edulis Linnaeus, 1758 and the king scallop Pecten maximus (Linnaeus, 1758)) were deployed at the gas release site and at a reference site—both within Ardmucknish Bay, Oban, Scotland. Replicate individuals were sampled at six time points over a 125-day period, which spanned both the 37-day injection and recovery phases of the experiment, in order to establish impacts to molecular physiology. Samples of bivalves were also simultaneously sampled from a reference site within the bay in order to contrast changes in physiology induced by the gas release with naturally variability in the physiological performance of both species. We present data on changes in the transcription of genes coding for key ionic and carbon dioxide regulatory proteins. There was no evidence of gene regulation of either selected carbonic anhydrases (CAx genes) or the alpha subunit of sodium potassium ATPAses (ATP1A genes) in individual bivalves collected from the CO2 gas release site, in either species. In the common mussel M. edulis there was only evidence for changes with time in the expression of genes coding for different classes of carbonic anhydrase. It was therefore concluded that the effects of the plume of elevated pCO2 on ion-regulatory gene transcription were negligible in both species. Whilst the analysed data from this current study do not constitute an impediment to the continued development of sub-seabed CCS as a climate mitigation strategy, further modelling is necessary to predict the consequences of larger or longer term leaks. Further analysis is also required in order to constrain the potential physiological impacts of gas leaks to benthic infaunal species and understand the mechanism of possible avoidance behaviour recorded in burrowing heart urchins Echinocardium cordatum (Pennant, 1777)

Size variation of 0-group plaice: Are earlier influences on growth potential a contributing factor?

Over a decade of sampling has shown that there are consistent differences in the sizes of 0-group plaice by late summer comparing 21 nursery sites on the Scottish west coast. However, when young fish were collected from two sites which produce particularly small and large fish and reared using a common garden design, growth rates between fish from the two sites were indistinguishable. Either there is little selection for fast or slow growth up to a few weeks post-settlement, or such effects do not persist sufficiently strongly to influence later growth. There were also no significant correlations between the time-series of fish size comparing sites, although within some sites there was evidence of inter-annual density-dependent effects. Any influences of offshore regional scale factors, such as sea temperature or pelagic primary productivity on growth thus appear to be heavily modified by local conditions on the nursery grounds. The field observations combined with the experimental results lead us to conclude that the size 0-group plaice attain in late summer is mainly controlled by post-settlement habitat quality