Small-scale patterns and processes in a soft-substratum, intertidal community

Experimental manipulations and direct observations were combined to study small-scale dispersion patterns and their causes in an intertidal sand-flat community numerically dominated by sessile and sedentary tube dwellers. Individuals of several species exhibited gregariousness at scales as small as one centimeter. Experiments in which needles were placed in sediments to simulate animal tubes suggested that organisms are affected by patterns of flow which change over distances of several millimeters to a centimeter

Flow disruption by an animal-tube mimic affects sediment bacterial colonization

Simple flume experiments demonstrate that local flow perturbations by a protruding animal-tube mimic can cause a significant increase in bacterial colonization at the sediment-seawater interface. The occurrence and extent of this increase depend on properties of the viscous sublayer adjoining the bed—specifically, its spatial and temporal continuity, and its thickness relative to tube height. In the field homologous tube effects on bacterial colonization and abundances are likely to be common. These effects are postulated to be important to larval recruitment, community composition, the nutrition of deposit feeders, and sediment dynamics

Larval settlement in turbulent pipe flows

In two experiments, larval settlement was studied within a series of pipes, each containing steady, turbulent, flowing seawater. The study was designed to determine effects of flow (speed, turbulence intensity and wall shear stress) and surface orientation on rates of settlement of larvae of various taxa, and to relate variability in patterns of settlement among orientations and flows to the concomitant variability expected in rates of larval supply or delivery to the pipe walls. Patterns of settlement of all five taxa (the barnacle Balanus spp., the mussel Mytilus trossulus, the serpulid polychaete Pseudochitinopoma occidentalis, the cyclostome bryozoan Tubulipora sp., and the terebellid polychaete Eupolymnia heterobranchia) generally conformed to predicted patterns of larval supply to pipe walls (the larval transport flux). Within each taxon results were consistent in the two experiments. For these taxa, the transport fluxes that most closely matched observed settlement fluxes were predicted by assuming that larvae exhibited average speeds of advection (by swimming or sinking) of comparatively low magnitude. These best-fit larval speeds are consistent with results from previous studies of larval swimming. However, some results indicate that settlement patterns also were affected significantly by processes operating after larval contact with pipe walls. In several instances settlement patterns exhibited a strong and significant effect of wall orientation that varied in intensity with flow speed in a manner not predictable from expected patterns of larval supply. The probable causes for this effect and statistical interaction vary among taxa, but in all cases involve consideration of the habitat, behavior or success of the post-settlement, benthic individual

Numerical modeling of larval settlement in turbulent bottom boundary layers

A time-dependent model of a tidal or wave bottom boundary layer has been developed to quantitatively evaluate the relative influences of vertical advection, turbulent mixing and shear, and near-bed behavior on settlement of planktonic larvae of benthic animals. The settlement behavior of larvae is modeled with a simple flux condition at the bed. This allows full time dependence to be included when determining settlement rates. For tidal oscillations, the model predicts that most settlement will occur at and near periods of slack water, whereas comparatively little settlement will occur during periods of stronger flow. In contrast, there should be little temporal variability in settlement rates associated with short-period wind waves. If larvae exhibit a relatively weak propensity to settle, then the settlement flux is small compared to the advective/turbulent flux of larvae supplied from higher in the water column to regions near the bed. In this case, a description of probability of settlement and a quasi-steady state suspension model fully describe the system. In contrast, when larvae exhibit a high settlement propensity, then the settlement flux is potentially larger than the advective/turbulent flux and the system is controlled by the hydrodynamic supply of larvae to the near-bed region. In this case, net settlement is governed primarily by larval fall velocity (a composite of gravitational sinking plus swimming) and turbulent shear stress. The ecological systems which are controlled by animal behavior or by physical processes may thus be identified by estimates of relatively simple parameters describing these fluxes

Sediment destabilization by animal tubes

Laboratory flume ex periments we re conducted in order to test the influence on sediment e rodibility of varying densities of the tube-building polychaete worm Owenia fusiformis. Experiments were performed on isolated individuals, in order to measure approximate spatial limits of isolated tube effects, and on arrays of individuals at densities reported previously to be associated with stable beds...

Performance of cages as large animal-exclusion devices in the deep sea

Sedimentary, deep-sea communities include megafaunal animals (e.g., sea cucumbers, brittle stars, crabs) and demersal fishes, collectively termed the large, motile epifauna (LME). Individuals of the LME are common, and their biomass approximates that of the macrofauna. Based on analogies with shallow-water animals, they are likely to be sources of mortality for the infauna and to create spatial and temporal heterogeneity in the community. Given present theories of deep-sea community organization, such effects could be important. Unfortunately, this hypothesis has not been tested because of the difficulty of conducting experiments in the deep sea and because tools for manipulating the LME have not been developed. We studied the suitability of exclusion cages for this purpose at 780 m depth in San Diego Trough. We placed 16 cages of two mesh sizes for 4.5 months over regions of the seafloor that appeared free of LME. Time-lapse photographs of a cage and a control plot coupled with observations of all cages at the end of the experiment indicated that small (1.27-cm × 1.27-cm square)-mesh cages were effective at excluding LME. Further, the cages were essentially free of cage artifacts that have been reported in shallow-water studies. Large, mobile and disruptive animals (e.g., fishes, crabs) did not establish long-term residence adjacent to or on the cages. Bio-fouling slightly reduced the open surface area of the cage mesh, potentially reducing flow through the cage, but the composition of surface sediments in terms of organic C and N, phytoplankton-derived pigments, and grain size was indistinguishable between cages and control areas. Activities of excess 234Th were significantly higher (average = 37%) inside of small-mesh cages, which might suggest enhanced particulate deposition inside cages. However, this measurement was an artifact of experimental manipulation. Particles that accumulated on the cage during the experiment were dislodged and settled to the seafloor when the cage was opened just prior to sampling. These particles would have been highly enriched in 234Th, and their inclusion in core samples artificially inflated the calculated sediment accumulation rates inside cages. Therefore, the cages performed well; they excluded the targeted LME without causing artifacts and thus should be useful for experimental study of a group of animals that may have substantial impact on the structure and organization of deep-sea communities

Factors associated with survival in a contemporary adult sickle cell disease cohort: Factors Associated with Survival in Sickle Cell Disease

We examined the relationship of clinical differences among sickle cell disease (SCD) patients in order to understand the major contributors to early mortality in a contemporary cohort

MYH9 and APOL1 are both associated with sickle cell disease nephropathy

Renal failure occurs in 5–18% of sickle cell disease (SCD) patients and is associated with early mortality. At risk SCD patients cannot be identified prior to the appearance of proteinuria and the pathobiology is not well understood. The MYH9 and APOL1 genes have been associated with risk for focal segmental glomerulosclerosis and end-stage renal disease in African Americans

Time-Space Clustering of Human Brucellosis, California, 1973–1992 1

Infection with Brucella spp. continues to pose a human health risk in California despite great strides in eradicating the disease from domestic animals. Clustering of human cases in time and space has important public health implications for understanding risk factors and sources of infection. Temporal-spatial clustering of human brucellosis in California for the 20-year period 1973–1992 was evaluated by the Ederer-Myers-Mantel, Moran’s I, and population-adjusted Moran’s I procedures. Cases were clustered in concentrated agricultural regions in the first 5-year interval (1973–1977). Time-space clustering of human brucellosis cases in California late in the 20-year study period may reflect the distribution of Hispanic populations. Public health programs in California should focus on educating Hispanic populations about the risk of consuming dairy products, such as soft cheeses, made from unpasteurized milk

Managing Bay and Estuarine Ecosystems for Multiple Services

Abstract Managers are moving from a model of managing individual sectors, human activities, or ecosystem services to an ecosystem-based management (EBM) approach which attempts to balance the range of services provided by ecosystems. Applying EBM is often difficult due to inherent tradeoffs in managing for different services. This challenge particularly holds for estuarine systems, which have been heavily altered in most regions and are often subject to intense management interventions. Estuarine managers can often choose among a range of management tactics to enhance a particular service; although some management actions will result in strong tradeoffs, others may enhance multiple services simultaneously. Management of estuarine ecosystems could be improved by distinguishing between optimal management actions for enhancing multiple services and those that have severe tradeoffs. This requires a framework that evaluates tradeoff scenarios and identifies management actions likely to benefit multiple services. We created a management action-services matrix as a first step towards assessing tradeoffs and providing managers with a DOI 10.1007/s12237-013-9602-7 decision support tool. We found that management actions that restored or enhanced natural vegetation (e.g., salt marsh and mangroves) and some shellfish (particularly oysters and oyster reef habitat) benefited multiple services. In contrast, management actions such as desalination, salt pond creation, sand mining, and large container shipping had large net negative effects on several of the other services considered in the matrix. Our framework provides resource managers a simple way to inform EBM decisions and can also be used as a first step in more sophisticated approaches that model service delivery