Role of habitat and predators in maintaining functional diversity of estuarine bivalves

Habitat loss is occurring rapidly in coastal systems worldwide. In Chesapeake Bay, USA, most historical oyster reefs have been decimated, and seagrass loss is expected to worsen due to climate warming and nutrient pollution. This loss of habitat may result in declining diversity, but whether diversity loss will equate to loss in ecosystem function is unknown. A bivalve survey was conducted in a variety of habitat types (seagrass, oyster shell, shell hash, coarse sand, detrital mud) in 3 lower Chesapeake Bay sub-estuaries from spring 2012 through summer 2013 to examine the correlation between bivalve densities, habitat type, habitat volume (of material retained on 3 mm mesh), and predator density. Bivalves were analyzed as functional groups based on feeding mode, living position, and predator defense strategy. On average, seagrass supported one additional functional group, and diversity was increased 68-94%, in seagrass compared to the other habitats examined. Species richness and functional group richness were positively correlated with habitat volume. The greatest densities of deposit-feeding bivalves were in detrital mud habitats, the greatest densities of thin-shelled and surface-dwelling bivalves were in seagrass habitats, and the greatest densities of armored bivalves were in oyster shell habitats. Small, thin-shelled bivalves were negatively correlated with densities of predators, including blue crabs Callinectes sapidus and cownose rays Rhinoptera bonasus. Overall, bivalve diversity was as - sociated with habitat type, habitat volume, and predator densities. These results suggest that all habitats, and particularly seagrass, play a role in maximizing bivalve functional diversity in Chesapeake Bay

Are predator−prey model predictions supported by empirical data? Evidence for a storm-driven shift toan alternative stable state in a crab−clam system

A dynamic systems approach can predict steady states in predator−prey interactions,but there are very few examples of predictions from predator−prey models conforming to empirical data. Here, we examined the evidence for the low-density steady state predicted by a Lotka-Volterra model of a crab−clam predator−prey system using data from long-term monitoring, and data from a previously published field survey and field predation experiment. Changepoint analysis of time series data indicate that a shift to low density occurred for the soft-shell clam Mya arenaria in 1972, the year of Tropical Storm Agnes. A possible mechanism for the shift is that Agnes altered predator−prey dynamics between M. arenaria and the blue crab Callinectes sapidus, shifting from a system controlled from the bottom up by prey resources, to a system controlled from the top down by predation pressure on bivalves, which is supported by a correlation analysis of time series data. Predator−prey ordinary differential equation models with these 2 species were analyzed for steady states, and low-density steady states were similar to previously published clam densities and mortality rates, consistent with the idea that C. sapidusis a major driver of M. arenaria population dynamics. Relatively simple models can predict shifts to alternative stable states,as shown by agreement between model predictions (this study) and published field data in this system. The preponderance of multispecies interactions exhibiting nonlinear dynamics indicatesthat this may be a general phenomenon

Weak Lensing Analysis of the z~0.8 cluster CL 0152-1357 with the Advanced Camera for Surveys

We present a weak lensing analysis of the X-ray luminous cluster CL 0152-1357 at z~0.84 using HST/ACS observations. The unparalleled resolution and sensitivity of ACS enable us to measure weakly distorted, faint background galaxies to the extent that the number density reaches ~175 arcmin^-2. The PSF of ACS has a complicated shape that also varies across the field. We construct a PSF model for ACS from an extensive investigation of 47 Tuc stars in a modestly crowded region. We show that this model PSF excellently describes the PSF variation pattern in the cluster observation when a slight adjustment of ellipticity is applied. The high number density of source galaxies and the accurate removal of the PSF effect through moment-based deconvolution allow us to restore the dark matter distribution of the cluster in great detail. The direct comparison of the mass map with the X-ray morphology from Chandra observations shows that the two peaks of intracluster medium traced by X-ray emission are lagging behind the corresponding dark matter clumps, indicative of an on-going merger. The overall mass profile of the cluster can be well described by an NFW profile with a scale radius of r_s =309+-45 kpc and a concentration parameter of c=3.7+-0.5. The mass estimates from the lensing analysis are consistent with those from X-ray and Sunyaev-Zeldovich analyses. The predicted velocity dispersion is also in good agreement with the spectroscopic measurement from VLT observations. In the adopted WMAP cosmology, the total projected mass and the mass-to-light ratio within 1 Mpc are estimated to be 4.92+-0.44 10^14 solar mass and 95+-8 solar mass/solar luminosity, respectively.Comment: Accepted for publication in Astrophysical Journal. 58 pages, 26 figures. Figures have been degraded to meet size limit; a higher resolution version available at http://acs.pha.jhu.edu/~mkjee/ms_cl0152.pd

Weak Lensing by High-Redshift Clusters of Galaxies - I: Cluster Mass Reconstruction

We present the results of a weak lensing survey of six high-redshift (z > 0.5), X-ray selected clusters of galaxies. We have obtained ultra-deep R-band images of each cluster with the Keck Telescope, and have measured a weak lensing signal from each cluster. From the background galaxy ellipticities we create two-dimensional maps of the surface mass density of each cluster. We find that the substructure seen in the mass reconstructions typically agree well with substructure in both the cluster galaxy distributions and X-ray images of the clusters. We also measure the one-dimensional radial profiles of the lensing signals and fit these with both isothermal spheres and "universal" CDM profiles. We find that the more massive clusters are less compact and not as well fit by isothermal spheres as the less massive clusters, possibly indicating that they are still in the process of collapse.Comment: 43 pages, 15 figures, uses aastex, submitted to ApJ 4 color plates produced here as jpg's, larger versions of the jpgs can be found at http://www.mpa-garching.mpg.de/~clow

Saved by the shell: Oyster reefs can shield juvenile blue crabs Callinectes sapidus

Juvenile blue crabs Callinectes sapidus use seagrass and other structured habitats as refuges from predation. Oyster reef habitats provide structural complexity that may offer refuge, but the value of these habitats for juvenile blue crabs has not been examined. We quantified survival of juvenile C. sapidus in structured oyster reef habitat versus unstructured soft-bottom habitat. In a field tethering experiment in the York River, lower Chesapeake Bay (USA), juvenile C.sapidus (10−50 mm carapace width [CW]) were tethered in sand (n = 40) or oyster reef (n = 39)habitats at subtidal sites 1−2 m deep. An underwater camera system was used to record predation activity during 24 h trials. Juvenile crab survival was significantly higher on the oyster reef habitat (53.8%) than on bare sand (15.0%), and tended to increase with crab CW in both habitats. The main successful predators on juvenile blue crabs were northern pufferfish Sphoeroides maculatus in the oyster reef habitat and adult blue crabs in the sand habitat. The high survival rate of juvenile C. sapidus in oyster reef habitats suggests that oyster reefs include physical habitat complexity that may offer refuge from predators. Restored and natural oyster reefs could provide an alternative nursery habitat for juvenile blue crabs, expanding the ecosystem services provided by restored oyster reefs

Individual, population, and ecosystem effects of hypoxia on a dominant benthic bivalve in Chesapeake Bay

Hypoxia is an environmental stressor that affects abundance, biomass,diversity, and ecosystem function of benthic assemblages worldwide, yet its collective impact at individual, population, and ecosystem levels has rarely been investigated. We examined the effects of hypoxia on the biomass-dominant clam,Macoma balthica, in the York and Rappahannock Rivers (Chesapeake Bay, USA). We (1) surveyed the M. balthica populationsin both rivers in 2003 and 2004, (2) determined the effects of low dissolved oxygen (DO) on M.balthica fecundity in a laboratory experiment, and (3) employed a predator-exclusion fieldexperiment to establish the effects of hypoxia and prey density on predation upon M. balthica.The resultant data were used to parameterize a matrix model, which was analyzed to define potential effects of hypoxia at the population level. In both rivers, hypoxia decreased individual clam growth and caused local extinction of populations. Hypoxia reduced egg production of M. balthicaby 40%and increased protein investment per egg. In the predator-exclusion field experiment, hypoxia magnified predation rates threefold and altered the functional response of predators toM. balthicafrom a stabilizing type III functional response to a destabilizing type II functional response. In a density-independent matrix model, hypoxia resulted in coupled source–sink metapopulation dynamics, with hypoxic areas acting as black-hole sinks. Increases in the spatial and temporal extent of hypoxia caused the populations to decline toward extinction. In a second model that incorporated density dependence, under mild hypoxic conditions trophic transfer from M. balthica to predators increased, but at increased spatial or temporal extent of hypoxia trophic transfer decreased. The major declinein trophic transfer to predators under severe hypoxia resulted from diversion of M. balthica biomass into the microbial loop. Our model predicted that there are multiple stable states forM. balthic apopulations (high and very low densities), such that the saddle point (threshold at which the population switches from one state to the other) increased and resilience decreased with the spatial extent of hypoxia. We underscore how effects of a stressor at the individual level can combine to have substantial population and ecosystem-level effect

Efficacy of blue crab spawning sanctuaries in Chesapeake Bay

Sanctuaries can potentially protect a significant fraction of the spawning stock, and thereby sustain heavily exploited populations. Despite the worldwide use of marine and estuarine spawning sanctuaries, the effectiveness of such sanctuaries remains untested. We therefore attempted to quantify the effectiveness of the spawning sanctuaries for adult female blue crabs (Callinectes sapidus) in Chesapeake Bay. We used baywide winter dredge survey data to estimate the potential spawning stock prior to the major exploitation period, and summer trawl survey data to estimate spawning stock abundance within the Lower Bay Spawning Sanctuary and adjacent Bayside Eastern Shore Sanctuary during the reproductive period. Hence, we were able to approximate the percentage of the potential spawning stock that was protected by both sanctuaries after exploitation. On average, approximately 16% of the potential spawning stock survived to reach the Lower Bay Spawning Sanctuary and Bayside Eastern Shore Sanctuary. Even under a best-case scenario (i.e., crab residence time of 2 weeks), the sanctuaries only protected an estimated 22% of the potential spawning stock, which is well below the percentage recommended by recent stock assessments for sustainable exploitation (28%). In the worst case, a mere 11% of the potential spawning stock survived to reach the spawning sanctuaries. Hence, we recommend a substantial expansion of the spawning sanctuaries, as well as the complementary protection of other life stages in critical habitats, such as nursery grounds and dispersal corridors. Furthermore, traditional fisheries management measures (e.g., effort control) should be used in concert with sanctuaries to thwart impediments to effective implementation of the sanctuaries, such as redirected fishing effort.https://scholarworks.wm.edu/vimsbooks/1084/thumbnail.jp

Transient thermal effects in solid noble gases as materials for the detection of Dark Matter

The transient phenomena produced in solid noble gases by the stopping of the recoils resulting from the elastic scattering processes of WIMPs from the galactic halo were modelled, as dependencies of the temperatures of lattice and electronic subsystems on the distance to the recoil's trajectory, and time from its passage. The peculiarities of these thermal transients produced in Ar, Kr and Xe were analysed for different initial temperatures and WIMP energies, and were correlated with the characteristics of the targets and with the energy loss of the recoils. The results were compared with the thermal spikes produced by the same WIMPs in Si and Ge. In the range of the energy of interest, up to tens of keV for the self-recoil, local phase transitions solid - liquid and even liquid - gas were found possible, and the threshold parameters were established.Comment: Minor corrections and updated references; accepted to JCA

Intense Star-formation and Feedback at High Redshift: Spatially-resolved Properties of the z=2.6 Submillimeter Galaxy SMMJ14011+0252

We present a detailed analysis of the spatially-resolved properties of the lensed submillimeter galaxy SMMJ14011+0252 at z=2.56, combining deep near-infrared integral-field data obtained with SPIFFI on the VLT with other multi-wavelength data sets. The broad characteristics of SMMJ14011+0252 are in agreement with what is expected for the early evolution of local massive spheroidal galaxies. From continuum and line flux, velocity, and dispersion maps, we measure the kinematics, star-formation rates, gas densities, and extinction for individual subcomponents. The star formation intensity is similar to low-redshift ``maximal starbursts'', while the line fluxes and the dynamics of the emission line gas provide direct evidence for a starburst-driven wind with physical properties very similar to local superwinds. We also find circumstantial evidence for "self-regulated" star formation within J1. The relative velocity of the bluer companion J2 yields a dynamical mass estimate for J1 within about 20 kpc, M_dyn \sim 1\times 10^{11} M_sun. The relative metallicity of J2 is 0.4 dex lower than in J1n/s, suggesting different star formation histories. SED fitting of the continuum peak J1c confirms and substantiates previous suggestions that this component is a z=0.25 interloper. When removing J1c, the stellar continuum and H-alpha line emission appear well aligned spatially in two individual components J1n and J1s, and coincide with two kinematically distinct regions in the velocity map, which might well indicate a merging system. This highlights the close similarity between SMGs and ULIRGs, which are often merger-driven maximal starbursts, and suggests that the intrinsic mechanisms of star-formation and related feedback are similar to low-redshift strongly star-forming systems.Comment: Some of the figures changed from b/w to colo