Vertical migration behavior and larval transport in brachyuran crabs

I documented the patterns of vertical distribution and abundance of zoeae from 3 families of brachyuran crabs in the York River, a sub-estuary in southern Chesapeake Bay (USA). The family groups included species from Ocypodidae, Pinnotheridae, and Panopeidae. I assessed the effects of Light and tidal current stage on the abundance and vertical distribution of zoeae using analysis of variance (ANOVA) and logistic regression. Clear behavioral patterns were evident in the logistic regression. Ocypodid larvae exhibited tidally timed behavior with larvae nearest the surface during ebb tides. Pinnotherid larval behaviors were correlated with both light and tidal current phase. Larvae were nearest the surface at night and during ebb tides. Panopeid larvae were near the bottom during early flood tides, near mid-depths during late flood and early ebb tides, and nearest the surface during late ebb tides. These behavioral patterns should result in horizontal distributions that are consistent with those observed in previous studies. The ANOVA reflected similar results; however, high variability between replicates weakened the significance of these patterns. The different analyses reflect processes on different spatial and temporal scales. The samples were replicated on short time scales (5 to 10 min). The logistic regression, a categorical analysis, largely ignores the variation between replicates and reflects average behaviors on the scale of several tidal cycles. In contrast, the ANOVA is highly sensitive to the variation between replicates and reflects patterns on scales of minutes. This high variation reflects turbulent vertical mixing and fine-scale horizontal patchiness in larval distribution. Small-scale physical processes that redistribute larvae both vertically and horizontally may have a strong influence on the variability in dispersal and recruitment success

Abundance and vertical distribution of drifting, post-larval Macoma spp. (Bivalvia : Tellinidae) in the York River, Virginia, USA

We sampled the early drifting post-larvae of a complex of 2 species of tellinid bivalves, Macoma spp., at a station in the lower York River, Chesapeake Bay, USA. Plankton samples were collected by pump every 3 h from 3 depths (surface, mid-depth, and bottom) on 4 dates corresponding to full and new moons. Macoma spp. post-larvae (size range 400 to 500 mu m) were abundant in the plank ton throughout the sampling period. The environmental factors influencing the abundance and vertical distribution of drifting post-larvae were evaluated using linear and logistic regression. Post-larvae were always more abundant during night as compared to day and were more abundant during nocturnal, flooding tides than during ebbing tides. In general, they were closer to the surface at night and during flood tides, though these patterns were highly variable. These data indicate that drifting post-larval bivalves use \u27selective tidal stream transport\u27 to promote upstream dispersal as observed in the postlarvae of other estuarine taxa (e.g, crabs and fish). The post-larval stage generally re-invades juvenile habitats following the export of larvae to the mouth of the parent estuary or nearshore continental shelf. We suggest that small drifting post-larval bivalves exert behavioral control over suspension in the water column. This life-history stage serves to maintain high densities of juveniles and adults in the upstream portions of the York River estuary despite downstream transport of early larval stages

An expansion of the MSVPA approach for quantifying predator-prey interactions in exploited fish communities

Ecosystem-based fisheries management requires tools to place fish-stock dynamics in the broader context of fishery, predator, and competitive removals. Multispecies virtual population analysis (MSVPA) is an approach to quantifying predator prey interactions and estimating the rates of predation mortality for exploited fish populations. Here, an extended MSVPA (MSVPA-X) is presented as an alternative to existing MSVPA approaches. Notably, MSVPA-X uses index-tuned VPA methods, applies a more flexible feeding model, and includes an alternative functional feeding response. The MSVPA-X model is applied to a western Atlantic fish community, focusing on Atlantic menhaden and its major fish predators, and a sensitivity analysis of major model parameters is presented. The sensitivity analysis highlights the need for adequate diet sampling. The MSVPA-X represents an improvement over previous approaches by increasing the flexibility to model seasonal and interannual dynamics in the strength of predator - prey interactions. Model results demonstrate that, for menhaden in particular, and forage fish in general, quantifying predation mortality is an important part of effective assessments of forage fish, their predators, and the fisheries of both

Incentivizing research into the effectiveness of medical devices

Introduction Medical devices (MDs) often obtain market authorization with much less clinical evidence than other health technologies, especially pharmaceuticals. This is due to a number of reasons. First, in contrast to pharmaceuticals, there is no legal requirement to conduct adequately controlled clinical studies, other than for ‘high-risk’ devices in some jurisdictions. In the US for example, high-risk devices and innovative lower-risk devices are required to demonstrate ‘reasonable assurance of safety and effectiveness’, which may imply clinical evidence based on randomized studies in many instances. In contrast, in the EU the requirement is to demonstrate adequate performance and safety, which can often be achieved by conducting observational studies such as registries [1, 2]. Secondly, the devices industry comprises many small and medium-size enterprises (SMEs), which would find the cost of conducting clinical studies, especially randomized controlled trials, prohibitive. However, although some larger manufacturers do undertake clinical studies of some of their products, manufacturers with similar products (called ‘fast-followers’) can often claim ‘substantial equivalence’ to a product that already has market authorization, thus avoiding the need to conduct costly and timeconsuming clinical studies. Since regulatory agencies often accept these claims of equivalence, for example under the 510(k) process in the US [3], this further reduces the incentives for manufacturers to conduct expensive clinical studies. Therefore, although device manufacturers have patent protection, they are often not granted data exclusivity in the same way as pharmaceutical manufacturers. Finally, unlike pharmaceuticals, devices are often modified once on the market, meaning that even if clinical evidence was available for the original version of the product, it may not necessarily be available for the version currently being marketed. For example in the US, one analysis showed that for 77 original market authorization applications for cardiac implantable electronic devices (e.g., pacemakers, implantable cardioverter-defibrillators) since 1979, the FDA approved 5829 ‘supplements’ reflecting product modifications in the period up until 2012. Of course, many of these product modifications were minor and unlikely to affect the performance of the device, but 37 % involved a change to the device’s design. In the vast majority of these cases the FDA deemed that new clinical data were not necessary for approval [4]. The lack of clinical evidence prior to product launch, especially evidence of comparative effectiveness, limits the possibilities for health technology assessment [2]. However, it should be remembered that clinical evidence can be gathered both pre-market (i.e., through conducting controlled clinical trials in an experimental setting), and postmarket, through clinical studies undertaken in regular clinical practice. Post-market effectiveness research may be more important for MDs than pharmaceuticals, as the performance of the device often depends on the interaction with the user (the so-called learning curve) [5]. This suggests that solutions to the problem of inadequate clinical evidence should address the issue of conducting clinical research in both the pre- and post-market phase. In this editorial we consider ways in which MD manufacturers could be incentivized to produce more clinical evidence to facilitate health technology assessments, including economic evaluations

Cost Effectiveness of a Pharmacy-Only Refill Program in a Large Urban HIV/AIDS Clinic in Uganda

HIV/AIDS clinics in Uganda and other low-income countries face increasing numbers of patients and workforce shortages. We performed a cost-effectiveness analysis comparing a Pharmacy-only Refill Program (PRP), a form of task-shifting, to the Standard of Care (SOC) at a large HIV/AIDS clinic in Uganda, the Infectious Diseases Institute (IDI). The PRP was started to reduce workforce shortages and optimize patient care by substituting pharmacy visits for SOC involving monthly physician visits for accessing antiretroviral medicines.We used a retrospective cohort analysis to compare the effectiveness of the PRP compared to SOC. Effectiveness was defined as Favorable Immune Response (FIR), measured as having a CD4 lymphocyte count of over 500 cells/µl at follow-up. We used multivariate logistic regression to assess the difference in FIR between patients in the PRP and SOC. We incorporated estimates of effectiveness into an incremental cost-effectiveness analysis performed from a limited societal perspective. We estimated costs from previous studies at IDI and conducted univariate and probabilistic sensitivity analyses. We identified 829 patients, 578 in the PRP and 251 in SOC. After 12.8 months (PRP) and 15.1 months (SOC) of follow-up, 18.9% of patients had a FIR, 18.6% in the PRP and 19.6% in SOC. There was a non-significant 9% decrease in the odds of having a FIR for PRP compared to SOC after adjusting for other variables (OR 0.93, 95% CI 0.55-1.58). The PRP was less costly than the SOC (US$520 vs. 655 annually, respectively). The incremental cost-effectiveness ratio comparing PRP to SOC was US$ 13,500 per FIR. PRP remained cost-effective at univariate and probabilistic sensitivity analysis.The PRP is more cost-effective than the standard of care. Similar task-shifting programs might help large HIV/AIDS clinics in Uganda and other low-income countries to cope with increasing numbers of patients seeking care

The HTA risk analysis chart: visualising the need for and potential value of managed entry agreements in health technology assessment

Background Recent changes to the regulatory landscape of pharmaceuticals may sometimes require reimbursement authorities to issue guidance on technologies that have a less mature evidence base. Decision makers need to be aware of risks associated with such health technology assessment (HTA) decisions and the potential to manage this risk through managed entry agreements (MEAs). Objective This work develops methods for quantifying risk associated with specific MEAs and for clearly communicating this to decision makers. Methods We develop the ‘HTA risk analysis chart’, in which we present the payer strategy and uncertainty burden (P-SUB) as a measure of overall risk. The P-SUB consists of the payer uncertainty burden (PUB), the risk stemming from decision uncertainty as to which is the truly optimal technology from the relevant set of technologies, and the payer strategy burden (PSB), the additional risk of approving a technology that is not expected to be optimal. We demonstrate the approach using three recent technology appraisals from the UK National Institute for Health and Clinical Excellence (NICE), each of which considered a price-based MEA. Results The HTA risk analysis chart was calculated using results from standard probabilistic sensitivity analyses. In all three HTAs, the new interventions were associated with substantial risk as measured by the P-SUB. For one of these technologies, the P-SUB was reduced to zero with the proposed price reduction, making this intervention cost effective with near complete certainty. For the other two, the risk reduced substantially with a much reduced PSB and a slightly increased PUB. Conclusions The HTA risk analysis chart shows the risk that the healthcare payer incurs under unresolved decision uncertainty and when considering recommending a technology that is not expected to be optimal given current evidence. This allows the simultaneous consideration of financial and data-collection MEA schemes in an easily understood format. The use of HTA risk analysis charts will help to ensure that MEAs are considered within a standard utility-maximising health economic decision-making framework