Predicting hepatic encephalopathy in patients with cirrhosis: A UK population-based study and validation of risk scores

BACKGROUND

HE is a common neurologic complication in cirrhosis associated with substantial disease and economic burden. HE symptoms are nonspecific and there are limited ways of identifying patients with cirrhosis at high risk of later developing HE. A risk score was previously developed to identify patients at risk of developing HE in a predominately male US cohort. Here, we evaluated the performance of the HE risk scores in a UK cohort study.

METHODS

Health care records from Clinical Practice Research Datalink and linked Hospital Episode Statistics were used to select patients with cirrhosis who were diagnosed with HE, confirmed by a diagnosis code for HE or a rifaximin-α prescription. The index date was the date of incident cirrhosis. The study period was from January 2003 to June 2019.

RESULTS

A total of 40,809 patients with cirrhosis were selected in the UK cohort, of whom 59% were male. A total of 1561 patients were diagnosed with HE. Applying the UK cohort to the baseline sensitivity risk cutoff (≥-11) from the US cohort provided a sensitivity of 92% and a negative predictive value of 99%. Within a longitudinal model, applying a sensitivity cutoff of ≥-3 to this cohort gave a sensitivity of 89% and a negative predictive value of 99%.

CONCLUSIONS

Using data from the UK, the previously developed HE risk scores were found to be reliable for selecting those most likely to progress to HE in patients with liver cirrhosis. Despite the HE risk scores originally being estimated using the data from a predominately male US cohort, the scores were validated and found to be generalizable to female patients.

Impact of COVID-19 on 1-Year Survival Outcomes in Hepatocellular Carcinoma: A Multicenter Cohort Study

INTRODUCTION

The COVID-19 pandemic has caused severe disruption of healthcare services worldwide and interrupted patients' access to essential services. During the first lockdown, many healthcare services were shut to all but emergencies. In this study, we aimed to determine the immediate and long-term indirect impact of COVID-19 health services utilisation on hepatocellular cancer (HCC) outcomes.

METHODS

A prospective cohort study was conducted from 1 March 2020 until 30 June 2020, correlating to the first wave of the COVID-19 pandemic. Patients were enrolled from tertiary hospitals in the UK and Germany with dedicated HCC management services. All patients with current or past HCC who were discussed at a multidisciplinary meeting (MDM) were identified. Any delay to treatment (DTT) and the effect on survival at one year were reported.

RESULTS

The median time to receipt of therapy following MDM discussion was 49 days. Patients with Barcelona Clinic Liver Cancer (BCLC) stages-A/B disease were more likely to experience DTT. Significant delays across all treatments for HCC were observed, but delay was most marked for those undergoing curative therapies. Even though severe delays were observed in curative HCC treatments, this did not translate into reduced survival in patients.

CONCLUSION

Interruption of routine healthcare services because of the COVID-19 pandemic caused severe delays in HCC treatment. However, DTT did not translate to reduced survival. Longer follow is important given the delay in therapy in those receiving curative therapy.

Multi-Agent Deep Reinforcement Learning for Multi-Robot Applications: A Survey

Deep reinforcement learning has produced many success stories in recent years. Some example fields in which these successes have taken place include mathematics, games, health care, and robotics. In this paper, we are especially interested in multi-agent deep reinforcement learning, where multiple agents present in the environment not only learn from their own experiences but also from each other and its applications in multi-robot systems. In many real-world scenarios, one robot might not be enough to complete the given task on its own, and, therefore, we might need to deploy multiple robots who work together towards a common global objective of finishing the task. Although multi-agent deep reinforcement learning and its applications in multi-robot systems are of tremendous significance from theoretical and applied standpoints, the latest survey in this domain dates to 2004 albeit for traditional learning applications as deep reinforcement learning was not invented. We classify the reviewed papers in our survey primarily based on their multi-robot applications. Our survey also discusses a few challenges that the current research in this domain faces and provides a potential list of future applications involving multi-robot systems that can benefit from advances in multi-agent deep reinforcement learning.

Perioperative intravenous contrast administration and the incidence of acute kidney injury after major gastrointestinal surgery: prospective, multicentre cohort study

BACKGROUND

This study aimed to determine the impact of preoperative exposure to intravenous contrast for CT and the risk of developing postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery.

METHODS

This prospective, multicentre cohort study included adults undergoing gastrointestinal resection, stoma reversal or liver resection. Both elective and emergency procedures were included. Preoperative exposure to intravenous contrast was defined as exposure to contrast administered for the purposes of CT up to 7 days before surgery. The primary endpoint was the rate of AKI within 7 days. Propensity score-matched models were adjusted for patient, disease and operative variables. In a sensitivity analysis, a propensity score-matched model explored the association between preoperative exposure to contrast and AKI in the first 48 h after surgery.

RESULTS

A total of 5378 patients were included across 173 centres. Overall, 1249 patients (23·2 per cent) received intravenous contrast. The overall rate of AKI within 7 days of surgery was 13·4 per cent (718 of 5378). In the propensity score-matched model, preoperative exposure to contrast was not associated with AKI within 7 days (odds ratio (OR) 0·95, 95 per cent c.i. 0·73 to 1·21; P = 0·669). The sensitivity analysis showed no association between preoperative contrast administration and AKI within 48 h after operation (OR 1·09, 0·84 to 1·41; P = 0·498).

CONCLUSION

There was no association between preoperative intravenous contrast administered for CT up to 7 days before surgery and postoperative AKI. Risk of contrast-induced nephropathy should not be used as a reason to avoid contrast-enhanced CT.

Real-world experience of regorafenib in patients with hepatocellular carcinoma: A multicenter United Kingdom study

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Background: Regorafenib was the first treatment to demonstrate a survival benefit in patients with HCC after progression on sorafenib. The RESORCE trial found that regorafenib improved overall survival with acceptable toxicity, in patients with disease progression on sorafenib who tolerated ≥400mg sorafenib daily and had Child-Pugh A liver function. Methods: We performed a multicentre, retrospective, observational study of patients with HCC receiving regorafenib in the UK, following its availability in April 2018. Results: Data on a total of 104 patients were included from April 2018–August 2019, and 80.8% were male. Age was collected in 85 patients, with a median of 68 years (range 22–86). 23.5% had NAFLD, 21.2% had ALD, 12.9% had HBV, and 3.5% had HCV. Prior management included sorafenib (100%), TACE (30.8%), resection (12.9%). Duration of sorafenib treatment was evaluable in 99/104 patients, and reported a median of 8.7 months (range 1.8–76.6). Duration of regorafenib treatment was evaluable in 92/104 patients, and reported a median of 3.9 months (range 0.0–15.7). Following treatment with regorafenib, 6 patients (5.8%) achieved partial response, 37 (35.6%) achieved stable disease and 45 (43.3%) had progressive disease as the best response. 15 (14.4%) were not assessed and 1 (1.1%) had mixed response. Survival data is immature with 62/101 (61.4%) patients alive at the time of census with median survival currently 6.5 months. Fatigue was the most frequent AE, with 69/88 patients (85.2%) for all grades. 12/88 patients (14.8%) had Grade 3 fatigue. Other significant AEs include hand-foot syndrome (6/85 patients [7.3%] had Grade 3) and diarrhoea (4/83 patients [4.9%] had Grade 3). Conclusions: The population in our real-world experience of regorafenib for HCC had a similar duration of prior sorafenib to those in the RESORCE trial. However, there was different balance of aetiologies with a lower proportion of patients with HBV and HCV. The rate of partial response is similar to the RESORCE trial with fewer patients achieving stable disease. The incidence of fatigue was higher, but the incidence of hand-foot syndrome and diarrhoea were lower. Further expansion and follow-up of this population is warranted.

The Model of Mortality with Incident Cirrhosis (MoMIC) and the model of Long-term Outlook of Mortality in Cirrhosis (LOMiC)

The purpose of this study was to produce two statistical survival models in those with cirrhosis utilising only routine parameters, including non-liver-related clinical factors that influence survival. The first model identified and utilised factors impacting short-term survival to 90-days post incident diagnosis, and a further model characterised factors that impacted survival following this acute phase. Data were from the Clinical Practice Research Datalink linked with Hospital Episode Statistics. Incident cases in patients ≥18 years were identified between 1998 and 2014. Patients that had prior history of cancer or had received liver transplants prior were excluded. Model-1 used a logistic regression model to predict mortality. Model-2 used data from those patients who survived 90 days, and used an extension of the Cox regression model, adjusting for time-dependent covariables. At 90 days, 23% of patients had died. Overall median survival was 3.7 years. Model-1: numerous predictors, prior comorbidities and decompensating events were incorporated. All comorbidities contributed to increased odds of death, with renal disease having the largest adjusted odds ratio (OR = 3.35, 95%CI 2.97-3.77). Model-2: covariables included cumulative admissions for liver disease-related events and admissions for infections. Significant covariates were renal disease (adjusted hazard ratio (HR = 2.89, 2.47-3.38)), elevated bilirubin levels (aHR = 1.38, 1.26-1.51) and low sodium levels (aHR = 2.26, 1.84-2.78). An internal validation demonstrated reliability of both models. In conclusion: two survival models that included parameters commonly recorded in routine clinical practice were generated that reliably forecast the risk of death in patients with cirrhosis: in the acute, post diagnosis phase, and following this critical, 90 day phase. This has implications for practice and helps better forecast the risk of mortality from cirrhosis using routinely recorded parameters without inputs from specialists.

New molecular methods to assess biodiversity. Potentials and pitfalls of DNA metabarcoding: a workshop report

This report presents the outcome of the joint work of PhD students and senior researchers working with DNA-based biodiversity assessment approaches with the goal to facilitate others the access to definitions and explanations about novel DNA-based methods. The work was performed during a PhD course (SLU PNS0169) at the Swedish University of Agricultural Sciences (SLU) in Uppsala, Sweden. The course was co-organized by the EU COST research network DNAqua-Net and the SLU Research Schools Focus on Soils and Water (FoSW) and Ecology - basics and applications. DNAqua-Net (COST Action CA15219, 2016-2020) is a network connecting researchers, water managers, politicians and other stakeholders with the aim to develop new genetic tools for bioassessment of aquatic ecosystems in Europe and beyond. The PhD course offered a comprehensive overview of the paradigm shift from traditional morphology-based species identification to novel identification approaches based on molecular markers. We covered the use of molecular tools in both basic research and applied use with a focus on aquatic ecosystem assessment, from species collection to the use of diversity in environmental legislation. The focus of the course was on DNA (meta)barcoding and aquatic organisms. The knowledge gained was shared with the general public by creating Wikipedia pages and through this collaborative Open Access publication, co-authored by all course participants.

UK nationals who received their medical degrees abroad: selection into, and subsequent performance in postgraduate training: a national data linkage study

OBJECTIVES

To compare the likelihood of success at selection into specialty training for doctors who were UK nationals but obtained their primary medical qualification (PMQ) from outside the UK ('UK overseas graduates') with other graduate groups based on their nationality and where they gained their PMQ. We also compared subsequent educational performance during postgraduate training between the graduate groups.

DESIGN

Observational study linking UK medical specialty recruitment data with postgraduate educational performance (Annual Review of Competence Progression (ARCP) ratings).

SETTING

Doctors recruited into national programmes of postgraduate specialist training in the UK from 2012 to 2016.

PARTICIPANTS

34 755 UK-based trainee doctors recruited into national specialty training programmes with at least one subsequent ARCP outcome reported during the study period, including 1108 UK overseas graduates.

MAIN OUTCOME MEASURES

Odds of being deemed appointable at specialty selection and subsequent odds of obtaining a less versus more satisfactory category of ARCP outcome.

RESULTS

UK overseas graduates were more likely to be deemed appointable compared with non-EU medical graduates who were not UK citizens (OR 1.29, 95% CI 1.16 to 1.42), although less so than UK (OR 0.25, 95% CI 0.23 to 0.27) or European graduates (OR 0.66, 95% CI 0.58 to 0.75). However, UK overseas graduates were subsequently more likely to receive a less satisfactory outcome at ARCP than other graduate groups. Adjusting for age, sex, experience and the economic disparity between country of nationality and place of qualification reduced intergroup differences.

CONCLUSIONS

The failure of recruitment patterns to mirror the ARCP data raises issues regarding consistency in selection and the deaneries' subsequent annual reviews. Excessive weight is possibly given to interview performance at specialty recruitment. Regulators and selectors should continue to develop robust processes for selection and assessment of doctors in training. Further support could be considered for UK overseas graduates returning to practice in the UK.

Development and validation of diagnostic triage criteria for liver disease from a minimum data set enabling the 'intelligent LFT' pathway for the automated assessment of deranged liver enzymes

BACKGROUND

Liver function tests (LFTs) are commonly abnormal; most patients with 'incidental' abnormal LFTs are not investigated appropriately and for those who are, current care pathways are geared to find an explanation for the abnormality by a lengthy process of investigation and exclusion, with costs to the patient and to the health service.

OBJECTIVE

To validate an intelligent automatable analysis tool (iLFT) for abnormal liver enzymes, which diagnoses common liver conditions, provides fibrosis stage and recommends management.

DESIGN

A retrospective case note review from three tertiary referral liver centres, with application of the iLFT algorithm and comparison with the clinician's final opinion as gold standard.

RESULTS

The iLFT algorithm in 91.3% of cases would have correctly recommended referral or management in primary care. In the majority of the rest of the cases, iLFT failed safe and recommended referral even when the final clinical diagnosis could have been managed in primary care. Diagnostic accuracy was achieved in 82.4% of cases, consistent with the fail-safe design of the algorithm. Two cases would have remained in primary care as per the algorithm outcome, however on clinical review had features of advanced fibrosis.

CONCLUSION

iLFT analysis of abnormal liver enzymes offers a safe and robust method of risk stratifying patients to the most appropriate care pathway as well as providing reliable diagnostic information based on a single blood draw, without repeated contacts with health services. Offers the possibility of high quality investigation and diagnosis to all patients rather than a tiny minority.

How can primary care enhance end-of-life care for liver disease? Qualitative study of general practitioners' perceptions and experiences

BACKGROUND

Liver disease is the third most common cause of premature death in the UK. The symptoms of terminal liver disease are often difficult to treat, but very few patients see a palliative care specialist and a high proportion die in hospital. Primary care has been identified as a setting where knowledge and awareness of liver disease is poor. Little is known about general practitioners' (GPs) perceptions of their role in managing end-stage liver disease.

OBJECTIVE

To explore GPs' experiences and perceptions of how primary care can enhance end-of-life care for patients with liver disease.

DESIGN

Qualitative interview study, thematic analysis.

PARTICIPANTS

Purposive sample of 25 GPs from five regions of England.

RESULTS

GPs expressed a desire to be more closely involved in end-of-life care for patients with liver disease but identified a number of factors that constrained their ability to contribute. These fell into three main areas; those relating directly to the condition, (symptom management and the need to combine a palliative care approach with ongoing medical interventions); issues arising from patients' social circumstances (stigma, social isolation and the social consequences of liver disease) and deficiencies in the organisation and delivery of services. Collaborative working with support from specialist hospital clinicians was regarded as essential, with GPs acknowledging their lack of experience and expertise in this area.

CONCLUSIONS

End-of-life care for patients with liver disease merits attention from both primary and secondary care services. Development of care pathways and equitable access to symptom relief should be a priority.

Abstract NS6: Born to Run: Advanced Practice Provider-Led Mobile Stroke Unit Care Measures Up to Vascular Neurologists’ Diagnosis and Management

Background: Mobile Stroke Units (MSU) are growing in numbers throughout the U.S. and abroad, with numerous staffing configurations, telemedicine, and differing imaging capabilities. We aimed to test the diagnostic accuracy and treatment safety, alongside time to diagnosis and treatment delivery of a novel advanced practice provider (APP) led MSU team.

Methods: We launched an MSU housing a hospital-grade Siemens Somatom CT with CTA capabilities, and hired APPs with advanced neurovascular practitioner board certification to lead field medical diagnosis and order/initiate treatment for encountered stroke patients. Consecutive MSU patients were evaluated for differences between APPs and Vascular Neurologists (VNs) diagnosis and management, and scene diagnosis and treatment times were collected.

Results: Agreement between APP field medical diagnosis and MD hospital diagnosis was 100%; stroke mimic diagnosis agreement was 98%. Overall agreement for field interpretation of CT/CTA was 97%, with discrepancies not associated with stroke treatment decisions. MDs’ agreement with APPs’ identification/treatment of ICH was 100%, and IVtPA treatment decisions 98% (APPs more conservative). Scene arrival to medical diagnosis (including clinical exam and imaging completion/interpretation) ranged from 7-10 minutes, of which 4 minutes were CT/CTA start to finish times. Scene arrival to IVtPA bolus ranged from 16 minutes to 33 minutes and was driven primarily by need for control of excessive hypertension, with scene arrival to start of nicardipine premix infusion ranging from 10-14 minutes.

Conclusions: Use of an APP-led MSU is safe and non-inferior to VN diagnosis/management, and may be faster than telemedicine guided MSU treatment.

Successful long-term outcome of liver transplantation in late-onset lysosomal acid lipase deficiency

Late-onset LAL deficiency, previously referred to as cholesteryl ester storage disorder, is a rare lysosomal storage disorder characterized by accumulation of cholesteryl esters. It has a heterogeneous clinical phenotype including abdominal pain, poor growth, hyperlipidemia with vascular complications and hepatosplenomegaly. End-stage liver disease may occur, but there are few reports of successful LT. There are also concerns that systemic manifestations of the disease might persist post-LT. We report a case with excellent outcome eight yr following LT. The subject was noted to have asymptomatic hepatosplenomegaly during an intercurrent illness, and LAL deficiency was confirmed with compound heterozygosity in the LIPA. Despite dietary fat restriction, he developed signs of progressive liver disease and subsequently developed hepatopulmonary syndrome. He underwent cadaveric LT at the age of nine and a half yr and recovered with prompt resolution of hepatopulmonary syndrome. Eight yr post-transplant he has normal growth, normal lipid profile, and liver and renal function tests. Liver histology showed no evidence of disease recurrence at this stage. LT in this subject resulted in an excellent functional correction of late-onset LAL deficiency.

Relation between drug-induced central nervous system effects and plasma levels of diazepam in man

Pharmacodynamic effects and plasma levels of diazepam were studied in healthy male volunteers at different dose levels. Responses to diazepam were quantified, using instruments which measured body sway (statometry) and psychomotor performance (stressalyser tests). High dose-related correlations were obtained between drug-induced changes in test parameters and drug plasma levels, both with regard to stimulant and depressive effects. Techniques were devised for evaluating and comparing the efficacy and usefulness of different types of tests, taking into account critical thresholds, slopes and error estimates, correcting for changes in predrug levels and control (nondrug) trials.

Enzymatic liver function capacity correlates with disease severity of patients with liver cirrhosis: a study with the LiMAx test

BACKGROUND

Assessment and quantification of actual liver function is crucial in patients with chronic liver disease to monitor disease progression and predict individual prognosis. Mathematical models, such as model for end-stage liver disease, are used for risk stratification of patients with chronic liver disease but do not include parameters that reflect the actual functional state of the liver.

AIM

We aimed to evaluate the potential of a (13)C-based liver function test as a stratification tool by comparison with other liver function tests and clinical parameters in a large sample of healthy controls and cirrhotic patients.

METHODS

We applied maximum liver function capacity (LiMAx) to evaluate actual liver function in 347 patients with cirrhosis and in 86 controls.

RESULTS

LiMAx showed strong negative correlation with Child-Pugh Score (r = -0.707; p < 0.001), MELD (r = -0.686; p < 0.001) and liver function tests. LiMAx was lower in patients with liver cirrhosis compared to healthy controls [99 (57-160) µg/kg/h vs. 412 (365-479) µg/kg/h, p < 0.001] and differed among Child-Pugh classes [a: 181 (144-227) µg/kg/h, b: 96 (62-132) µg/kg/h and c: 52 (37-81) µg/kg/h; p < 0.001]. When stratified patients according to disease severity, LiMAx results were not different between cirrhotic patients and cirrhotic patients with transjugular intrahepatic portosystemic shunt.

CONCLUSIONS

LiMAx appears to provide reliable information on remnant enzymatic liver function in chronic liver disease and allows graduation of disease severity.

Predictors of quality of life in patients evaluated for liver transplantation

INTRODUCTION

Health-related quality of life (HRQOL) is severely impaired in advanced liver disease. The purpose of this study was to evaluate the impact of actual liver function and disease-specific factors on HRQOL of patients evaluated for liver transplantation.

PATIENTS AND METHODS

Disease-specific QOL was analyzed in 142 patients evaluated for liver transplantation using the German version of the Chronic Liver Disease Questionnaire (CLDQ-D). We performed quantitative liver function tests and collected clinical and demographical data of patients after their referral to our transplant department. Values were correlated with CLDQ-D scores.

RESULTS

Neither model for end-stage liver disease (MELD) nor dynamic liver function test results were related to quality of life. Serum albumin concentration was a strong but not independent factor correlated with global CLDQ-D (r = 0.269, p < 0.001). Independent predictors of global CLDQ-D were ascites and butyrylcholinesterase serum concentration (B = -0.486, p < 0.001 and B = 0.196, p = 0.002, respectively).

CONCLUSION

Actual liver function is not related to decreased quality of life, whereas ascites and hypoproteinemia represent the major factors influencing physical and social aspects of daily life in potential liver transplant candidates.

A novel personal health system with integrated decision support and guidance for the management of chronic liver disease

A personal health system platform for the management of patients with chronic liver disease that incorporates a novel approach to integrate decision support and guidance through care pathways for patients and their doctors is presented in this paper. The personal health system incorporates an integrated decision support engine that guides patients and doctors through the management of the disease by issuing tasks and providing recommendations to both the care team and the patient and by controlling the execution of a Care Flow Plan based on the results of tasks and the monitored health status of the patient. This Care Flow Plan represents a formal, business process based model of disease management designed off-line by domain experts on the basis of clinical guidelines, knowledge of care pathways and an organisational model for integrated, patient-centred care. In this way, remote monitoring and treatment are dynamically adapted to the patient's actual condition and clinical symptoms and allow flexible delivery of care with close integration of specialists, therapists and care-givers.

A prospective study evaluating the clinical relevance of a chemoresponse assay for treatment of patients with persistent or recurrent ovarian cancer

OBJECTIVE

Use of in vitro chemoresponse assays for informing effective treatment selection is a compelling clinical question and a topic of debate among oncologists. A prospective study was conducted evaluating the use of a chemoresponse assay in recurrent ovarian cancer patients.

METHODS

Women with persistent or recurrent ovarian cancer were enrolled under an IRB-approved protocol, and fresh tissue samples were collected for chemoresponse testing. Patients were treated with one of 15 protocol-designated treatments empirically selected by the oncologist, blinded to the assay results. Each treatment was classified by the assay as: sensitive (S), intermediate (I), or resistant (R). Patients were prospectively monitored for progression-free survival (PFS) and overall survival (OS). Associations of assay response for the physician-selected treatment with PFS and OS were analyzed.

RESULTS

A total of 262 evaluable patients were enrolled. Patients treated with an assay-sensitive regimen demonstrated significantly improved PFS and OS while there was no difference in clinical outcomes between I and R groups. Median PFS was 8.8 months for S vs. 5.9 months for I+R (hazard ratio [HR]=0.67, p=0.009). The association with assay response was consistent in both platinum-sensitive and platinum-resistant tumors (HR: 0.71 vs. 0.66) and was independent of other covariates in multivariate analysis (HR=0.66, p=0.020). A statistically significant14-month improvement in mean OS (37.5 months for S vs. 23.9 months for I+R, HR=0.61, p=0.010) was demonstrated.

CONCLUSIONS

This prospective study demonstrated improved PFS and OS for patients with either platinum-sensitive or platinum-resistant recurrent ovarian cancer treated with assay-sensitive agents.

Towards improved socio-economic assessments of ocean acidification's impacts

Ocean acidification is increasingly recognized as a component of global change that could have a wide range of impacts on marine organisms, the ecosystems they live in, and the goods and services they provide humankind. Assessment of these potential socio-economic impacts requires integrated efforts between biologists, chemists, oceanographers, economists and social scientists. But because ocean acidification is a new research area, significant knowledge gaps are preventing economists from estimating its welfare impacts. For instance, economic data on the impact of ocean acidification on significant markets such as fisheries, aquaculture and tourism are very limited (if not non-existent), and non-market valuation studies on this topic are not yet available. Our paper summarizes the current understanding of future OA impacts and sets out what further information is required for economists to assess socio-economic impacts of ocean acidification. Our aim is to provide clear directions for multidisciplinary collaborative research.

Impact of aragonite saturation state changes on migratory pteropods

Thecosome pteropods play a key role in the food web of various marine ecosystems and they calcify, secreting the unstable CaCO(3) mineral aragonite to form their shell material. Here, we have estimated the effect of ocean acidification on pteropod calcification by exploiting empirical relationships between their gross calcification rates (CaCO(3) precipitation) and aragonite saturation state Ω(a), combined with model projections of future Ω(a). These were corrected for modern model-data bias and taken over the depth range where pteropods are observed to migrate vertically. Results indicate large reductions in gross calcification at temperate and high latitudes. Over much of the Arctic, the pteropod Limacina helicina will become unable to precipitate CaCO(3) by the end of the century under the IPCC SRES A2 scenario. These results emphasize concerns over the future of shelled pteropods, particularly L. helicina in high latitudes. Shell-less L. helicina are not known to have ever existed nor would we expect them to survive. Declines of pteropod populations could drive dramatic ecological changes in the various pelagic ecosystems in which they play a critical role.

Segregation of Beaufort Sea beluga whales during the open-water season

Population segregation by habitat use occurs because energy requirements and survival strategies vary with age, sex, size, and reproductive stage. From late summer to early fall in 1993, 1995, and 1997, relative length (age), sex, and reproductive status of satellite-tagged beluga whales ( Delphinapterus leucas (Pallas, 1776)) in the eastern Beaufort Sea were tested for habitat segregation. We used (i) resource selection function models to evaluate how belugas used areas of varying sea ice concentration and shelf habitat and (ii) distance analysis to measure the selection of areas varying in distance to mainland and island coastlines. Resource selection functions and distance analysis established that habitat selection differed with length, sex, and reproductive status of whales: (i) females with calves and smaller males selected open-water habitats near the mainland; (ii) large males selected closed sea ice cover in and near the Arctic Archipelago; and (iii) smaller males and two females with calves (not newborn) selected habitat near the ice edge. The segregation of habitat use according to sex, age, and reproductive status relates to the different resources required at different life stages and may represent characteristics of beluga social structure. We discuss our results in the context of two common sexual segregation hypotheses and conclude that summer habitat segregation of belugas reflects differences in foraging ecology, risk of predation, and reproduction.