The distribution of the sum of negative binomial random variables has a special role in insurance mathematics, actuarial sciences, and ecology. Two methods to estimate this distribution have been ...published: a finite-sum exact expression and a series expression by convolution. We compare both methods, as well as a new normalized saddlepoint approximation, and normal and single distribution negative binomial approximations. We show that the exact series expression used lots of memory when the number of random variables was high (>7). The normalized saddlepoint approximation gives an output with a high relative error (around 3–5%), which can be a problem in some situations. The convolution method is a good compromise for applied practitioners, considering the amount of memory used, the computing time, and the precision of the estimates. However, a simplistic implementation of the algorithm could produce incorrect results due to the non-monotony of the convergence rate. The tolerance limit must be chosen depending on the expected magnitude order of the estimate, for which we used the answer generated by the saddlepoint approximation. Finally, the normal and negative binomial approximations should not be used, as they produced outputs with a very low accuracy.
Organochlorine (OC) pesticides and the more persistent polychlorinated biphenyls (PCBs) have well-established dose-dependent toxicities to birds, fish and mammals in experimental studies, but the ...actual impact of OC pollutants on European marine top predators remains unknown. Here we show that several cetacean species have very high mean blubber PCB concentrations likely to cause population declines and suppress population recovery. In a large pan-European meta-analysis of stranded (n = 929) or biopsied (n = 152) cetaceans, three out of four species:- striped dolphins (SDs), bottlenose dolphins (BNDs) and killer whales (KWs) had mean PCB levels that markedly exceeded all known marine mammal PCB toxicity thresholds. Some locations (e.g. western Mediterranean Sea, south-west Iberian Peninsula) are global PCB "hotspots" for marine mammals. Blubber PCB concentrations initially declined following a mid-1980s EU ban, but have since stabilised in UK harbour porpoises and SDs in the western Mediterranean Sea. Some small or declining populations of BNDs and KWs in the NE Atlantic were associated with low recruitment, consistent with PCB-induced reproductive toxicity. Despite regulations and mitigation measures to reduce PCB pollution, their biomagnification in marine food webs continues to cause severe impacts among cetacean top predators in European seas.
1. Stable isotope data are widely used to track the origins and transformations of materials in food webs. Reliable interpretation of these data requires knowledge of the factors influencing isotopic ...fractionation between diet and consumer. For practical reasons, isotopic fractionation is often assumed to be constant but, in reality, a range of factors may affect fractionation. 2. To investigate effects of temperature and feeding rate on fractionation of carbon and nitrogen stable isotopes in a marine predator, we reared European sea bass Dicentrarchus labrax on identical diets at 11 and 16 °C on three ration levels for 600 days. 3. Nitrogen trophic fractionation (Δδ¹⁵N) was affected by temperature. Bass Δδ¹⁵N was 4·41per thousand at 11 °C and 3·78per thousand at 16 °C. 4. Carbon fractionation (Δδ¹³C) was also affected by temperature. Bass Δδ¹³C was 1·18per thousand at 11 °C and 1·64per thousand at 16 °C. The higher lipid content in the tissues of bass reared at cooler temperatures accounted for the temperature effect on Δδ¹³C. When Δδ¹³C was determined using mathematically defatted values, there was a direct effect of ration size and Δδ¹³C was 2·51, 2·39 and 2·31per thousand for high, medium and low rations, respectively. 5. Reported Δδ¹⁵N for all treatments exceeded the mean of 3·4per thousand widely used in ecological studies of fish populations and communities. This would confound the interpretation of δ¹⁵N as an indicator of trophic level when comparing populations that are exposed to different temperatures. 6. The Δδ¹³C of 0-1per thousand commonly applied in food web studies did not hold under any of the temperature or feeding regimes considered and a value of 2per thousand would be more appropriate.
Bivalve filter feeders, such as oysters, filter large volumes of water and are particularly exposed to microplastics (MP). Consequently, these animals digest and assimilate high levels of MP in their ...bodies that may likely impact their physiology, and potentially affect shellfish stocks, benthic habitats and, indirectly, the health status of the marine ecosystem and human consumers. In this study we exposed juvenile oysters, Crassostrea gigas, to 3 different MP concentrations (104, 105 and 106 particles L−1), represented by 6μm Polystyrene (PS) microbeads, compared to a control treatment receiving no MP. The study ran for a period of 80 days to test for the impacts of MP on growth, Condition Index and Lysosomal Stability. From histological analysis, microbeads were detected in the intestines of exposed oysters and in the digestive tubules, but no cellular inflammatory features were observed over time. Weight and shell length remained comparable between the different treatments and control. We found that Condition Index in the highest concentration increased initially but significantly reduced over time. The oysters in the highest MP exposure also showed the lowest mean Lysosomal Stability score throughout the experiment. Lysosomes play a vital role in the cells defense mechanisms and breakdown of constituents, crucial for the oysters’ wellbeing. Most importantly, we detected an increased mortality in those oysters who were chronically exposed to the highest loads of MP.
Aquaculture; Aquatic ecology; Ecological health; Environmental hazard; Environmental health; Environmental science; Environmental toxicology; Wastewater management; Water pollution; Microplastics; Pacific oyster; Long term exposure; Lysosomal stability; Condition index; Histology; Polystyrene microbeads
Seafloor sediments have been defined as sinks for microplastics in the marine environment and could therefore represent suitable matrices for their long-term monitoring. On a regional aspect, the ...adoption of a common indicator for microplastics in seafloor sediments would allow regional monitoring and assessments through international frameworks such as OSPAR. This study presents the findings of a research and development project monitoring the occurrence and abundance of microplastics in UK seafloor sediments for the period 2013-2021, supporting the development of a national monitoring programme for microplastics in seafloor sediments for the UK (England and Wales). A fast-screening technique based on Nile Red staining of polymers coupled with µ-FTIR was applied and validated using µ-FTIR-FPA. Microplastic particles were detected in all 189 sediment samples from 15 stations selected around the UK for each investigated year (2013 - 2021). Microplastic concentrations (20 – 5000 µm) ranged from 133 – 6,933 particles kg
-1
dry weight sediment for 2020-2021. Microplastics mainly consisted of fragments (73%), fibres (19%) and spheres (8%). Plastic fragments ranged from 46 to 3276 µm and plastic fibres from 300 to 1731 µm in length with a mean diameter of 16 µm. Single particle analysis using µ-FTIR indicated a prevalence of Rayon, PP, Rayon/Nylon/Polyester blends, Rubber, PS, PE, PA, PVC, Acrylic, EMAA and PET. Fragments were mainly white in colour (46%) followed by brown (38%), black (1%), blue (1%) and orange (1%). Fibres were mainly white in colour (57%) followed by black (14%), orange (14%) and red (14%). A trend assessment at the UK regional seas levels indicated little visual evidence of any trends in the abundance of microplastics over time in any of the regional seas – with the possible exception of the Northern North Sea with a reduction in abundance over time for the time-period 2013-2021.
This study documented the levels of microplastics in three commercially important small pelagic fish species in South African waters, namely European anchovy (Engraulis encrasicolus), West Coast ...round herring (Etrumeus whiteheadi) and South African sardine (Sardinops sagax). Data suggested variation between species with a higher concentration of microplastics for S. sagax (mean of 1.58 items individual-1) compared to Et. whiteheadi (1.38 items individual-1) and En. encrasicolus (1.13 items individual-1). The occurrence of microplastics was also higher for S. sagax (72%) and Et. whiteheadi (72%) compared to En. encrasicolus (57%). Microfibres accounted for 80% of ingested microplastics (the remainder were plastic fragments) with the main ingested polymers being poly(ethylene:propylene:diene) (33% occurrence), polyethylene (20%), polyamide (20%), polyester (20%) and polypropylene (7%). The abundance of ingested items was not significantly correlated with fish caudal length or body weight, and spatial investigation indicated an increase in the abundance of ingested items from the West to the South coast. Etrumeus whiteheadi is proposed as a bio-indicator for microplastics for South Africa.
Controls were placed on the production and use of the penta-mix polybrominated diphenyl ether (PBDE) formulation within the European Union in 2004. In porpoises stranded or bycaught around the U.K., ...BDE congeners from this product predominate. Lipid-normalized concentrations of 9 (summed) BDE congeners in the blubber of 415 porpoises sampled during the period 1992−2008 have been investigated for possible time trends resulting from the regulatory action. Our analysis suggests that, overall, median Σ9BDE concentrations peaked around 1998 and have since reduced by between 53.8% and 73.5% to 2008. Our best point estimate is that the reduction has been 67.6%. This decline was highly statistically significant (p < 0.001) and was not confounded by a range of other factors which were also considered (area, season, nutritional status, bycaught/stranded, and age class).
The assessment of eutrophic conditions is a formal requirement of several European Directives. Typically, these eutrophication assessments use a set of primary indicators which include dissolved ...inorganic nutrients, chlorophyll, dissolved oxygen and secondary information which can include phytoplankton community data. Each directive is characterised by a different geographical or political boundary which defines the area under assessment. Several disparate sources of data from the Thames estuary and Liverpool Bay in the United Kingdom collected from different monitoring programs were combined to generate a fully integrated dataset. Data sources included remote sensing, ecosystem models, moorings, freshwater inputs, and traditional ship surveys. Different methods were explored for assigning ecologically relevant assessment areas including delineation of the assessment area based on salinity, extent of the river plume influence and ecohydrodynamic characteristics in addition to the traditional geographically defined typologies associated with the different directives. Individual eutrophication indicators were tested across these revised typologies and outcomes of the different metrics compared across the river to marine continuum for the two UK areas. There have been statistically significant decreasing trends in the loads of ammonium, nitrite and dissolved inorganic phosphorous between 1994 and 2016 to both the Thames estuary and Liverpool Bay study areas but no statistically significant trends in loads of nitrate or dissolved inorganic nitrogen. There have been statistically significant increases in riverine nitrogen:phosphorous between 1994 and 2016. Nutrient concentrations exceeded assessment thresholds across nearly all areas other than the large offshore assessment areas and outcomes of the chlorophyll metric were often below assessment thresholds in the estuarine based areas and the offshore areas, but exceedances of thresholds occurred in the near coastal areas. However, trait-based indicators of phytoplankton community using functional groups show changes in plankton community structure over the assessment period indicating that additional metrics which quantify community shifts would be a useful measurement to include in future eutrophication assessments.
This assessment of environmental drivers and phytoplankton community in Kuwait (Arabian Gulf) arises from a scenario in which the rapid urbanisation in recent decades has caused significant changes ...from pre-industrial conditions. To present these changes, we have analysed a long-term water quality dataset (1984 – 2017) and explored potential changes in a sub-set of phytoplankton community data by analyzing ten years of phytoplankton data available (2007 – 2016) for Kuwait Bay and the Northern Gulf waters. The longer-term water quality data shows that dissolved nutrient concentration, with the exception of a recent fall in SiO4, have been increasing over 30 years but with a high degree of variability reflecting the changing rate of inputs from coastal pollution and the Shatt Al-Arab River. The correlative analysis between the environmental parameters and phytoplankton in the period from 2007 to 2016 show the seasonal variability of the phytoplankton are influenced by several factors stressors including higher temperatures, coastal sewage runoff, and changing salinity. Whilst the rapid and extended nutrient enrichment data move Kuwait coastal waters into a eutrophic state, the temporal patterns highlight that recent changes in phytoplankton community are more likely to be responding to cumulative pressures of eutrophication, climate and salinity changes. The seasonal and temporal changes in the coastal phytoplankton community, alongside long term deteriorating water quality present management challenges of managing local and external pressures. Continued declines in water quality within a system that is influenced by a warming climate can potentially have long-term consequences on the resilience of the Northern Gulf environment.
PDF
