Joint Effects of Population Density and Toxicant Exposure on Population Dynamics of \u3ci\u3eCapitella\u3c/i\u3e Sp. I

Very few studies have analyzed the dependence of population growth rate on population density, and even fewer have considered interaction effects of density and other stresses, such as exposure to toxic chemicals. Yet without such studies we cannot know whether chemicals harmful at low density have effects on carrying capacity or, conversely, whether chemicals reducing carrying capacity are also harmful at low density, impeding a population’s capacity to recover from disturbance. This study examines the combined effects of population density and a toxicant (fluoranthene) on population growth rate (pgr) and carrying capacity using the deposit-feeding polychaete Capitella sp. I as a test organism. Populations were initiated with a stable age distribution, and population density and age/size distribution were followed during a period of 28 wk. Fluoranthene (FLU), population density, and their interaction influenced population growth rate. Population growth rate declined linearly with the logarithm of population biomass, but the slope of the relationship was steeper for the control populations than for populations exposed to 50 μg FLU/(g sediment dry mass). Populations exposed to 150 μg FLU/(g sediment dry mass) went extinct after 8 wk of exposure. Despite concerns that toxicant effects would be exacerbated at high density, we found the reverse to be the case, and effects of fluoranthene on population growth rate were much reduced in the region of carrying capacity. Fluoranthene did reduce carrying capacity by 46%, and this could have important implications for interacting species and/or sediment biogeochemical processes

The influence of predation on the chronic response of Artemia sp. populations to a toxicant

Environmental risk assessment of contaminants is conventionally based on toxic effects assessed in organism-level test systems. We suggest that, for the prediction of toxicant effects, population- and community-level effects should be considered. The aim of this study was to investigate how predation could alter a prey population's response to a toxicant to reveal effects at population and community levels.Populations of the brine shrimp Artemia sp. were maintained in the laboratory with and without simulated predation. Individuals were exposed for 1 h to the pyrethroid insecticide esfenvalerate (0, 0·01, 0·04 and 0·08 µg L−1) and subsequently observed for 6 weeks.Unpredated exposed populations showed a reduced population density compared with the control. However, even at the highest concentration of insecticide, populations were sustained until the end of the experiment. The lower density in the exposed populations led to reduced competition and subsequently to enhanced development of surviving individuals and an increased proportion of young individuals. In contrast, the combination of predation and short-term toxicant exposure at concentrations of 0·04 and 0·08 µg L−1 produced extinction of the populations after 39 and 32 days of exposure, respectively.Synthesis and applications. The response of populations of brine shrimp to toxicants at the community level may be stronger when predation is present than the response of populations without predation pressure, as the regulation capacity of the population (measured as an increased production of offspring at reduced population densities) is exhausted when predation is present. Future ecotoxicological risk assessment schemes should consider relevant community characteristics such as predation as part of an environmental risk assessment

Genotoxic damage in polychaetes: a study of species and cell-type sensitivities.

addresses: School of Biosciences, Hatherley Laboratories, University of Exeter, Prince of Wales Road, Exeter EX4 4PS, UK. [email protected]: Journal Article; Research Support, Non-U.S. Gov'tCopyright © 2008 Elsevier. NOTICE: This is the author’s version of a work accepted for publication by Elsevier. Changes resulting from the publishing process, including peer review, editing, corrections, structural formatting and other quality control mechanisms, may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Mutation Research - Genetic Toxicology and Environmental Mutagenesis, 2008, Vol. 654, Issue 1, pp. 69 – 75 DOI: http://dx.doi.org/10.1016/j.mrgentox.2008.05.008The marine environment is becoming increasingly contaminated by environmental pollutants with the potential to damage DNA, with marine sediments acting as a sink for many of these contaminants. Understanding genotoxic responses in sediment-dwelling marine organisms, such as polychaetes, is therefore of increasing importance. This study is an exploration of species-specific and cell-specific differences in cell sensitivities to DNA-damaging agents in polychaete worms, aimed at increasing fundamental knowledge of their responses to genotoxic damage. The sensitivities of coelomocytes from three polychaetes species of high ecological relevance, i.e. the lugworm Arenicola marina, the harbour ragworm Nereis diversicolor and the king ragworm Nereis virens to genotoxic damage are compared, and differences in sensitivities of their different coelomic cell types determined by use of the comet assay. A. marina was found to be the most sensitive to genotoxic damage induced by the direct-acting mutagen methyl methanesulfonate (MMS), and showed dose-dependent responses to MMS and the polycyclic aromatic hydrocarbon benzo(a)pyrene. Significant differences in sensitivity were also measured for the different types of coelomocyte. Eleocytes were more sensitive to induction of DNA damage than amoebocytes in both N. virens and N. diversicolor. Spermatozoa from A. marina showed significant DNA damage following in vitro exposure to MMS, but were less sensitive to DNA damage than coelomocytes. This investigation has clearly demonstrated that different cell types within the same species and different species within the polychaetes show significantly different responses to genotoxic insult. These findings are discussed in terms of the relationship between cell function and sensitivity and their implications for the use of polychaetes in environmental genotoxicity studies

Effects of fluoranthene and ambient oxygen levels on survival and metabolism in three sibling species of \u3ci\u3eCapitella\u3c/i\u3e (Polychaeta)

The successful persistence of Capitella spp. in disturbed and/or oil-polluted habitats is widely known, but demographic adaptations might be only part of the explanation and little is known about differences among species. The present study investigates ecophysiological effects of the common PAH (polycyclic aromatic hydrocarbon) fluoranthene (FLU) on juvenile and adult survival, comparing 3 sibling species of Capitella (Polychaeta; Capitellidae). Subsequently, the influence of FLU on the aerobic and anaerobic metabolism in the most \u27sensitive\u27 species, Capitella sp. S, and most \u27tolerant\u27 species, Capitella sp. I, was assessed. Oxygen uptake and internal succinate concentration (an indicator of anaerobic metabolism) were measured after short-term (7 h) and long-term (2 wk) FLU pre-exposure (100 μg g–1). FLU exposure reduced mean survival times of juveniles (4 d old) of all sibling species, but tolerance varied among the 3 species of Capitella adults. Capitella sp. S, originally collected from \u27clean\u27 oxygen-rich North Sea intertidal sediments, was most sensitive and Capitella sp. M, and Capitella sp. I, which is the most opportunistic of the sibling species described to date, were most tolerant. In Capitella sp. S, O2 uptake decreased at lower ambient oxygen levels and increasing FLU concentrations increased oxygen consumption. Similarly, O2 uptake decreased at lower ambient oxygen levels in Capitella sp. I; however, FLU concentrations had no effect on oxygen uptake. For both species, anaerobic metabolism increased with declining ambient oxygen levels, and was influenced by FLU exposure in Capitella sp. S, but not in Capitella sp. I. Part of the explanation for the success of Capitella sp. I in oil-polluted habitats may be that this species is able to channel energy into vital processes without a measurable increase in energy expenditure. We conclude that these 3 Capitella species are ecophysiologically diverse in their responses to toxicant exposure. Our results suggest that toxicant tolerance differences among sibling species have a genetic basis and that increased aerobic and anaerobic metabolic rates in response to toxicant exposure can have negative survival consequences. This has to be considered when using these species as pollution indicators or to improve sediment quality

Density-dependent effects of a toxicant on life-history traits and population dynamics of a capitellid polychaete

The toxic effects of the widespread polycyclic aromatic hydrocarbon (PAH), fluoranthene (FLU), on Life-history traits of Capitella sp. M as a function of population density were investigated in a life-table-response-experiment (LTRE) lasting 134 d. Animals from laboratory cultures were exposed to 6 different FLU concentrations (range 0 to 80 μg FLU [g dry wt sed]–1, ppm) at 3 population densities (range 529 to 36 842 worms m–2), and survivorship, growth rate until maturity, and reproductive parameters were recorded. Fluoranthene exposure significantly reduced juvenile survivorship in a concentration- dependent manner, whereas population density had no effect on this trait. In contrast, increasing density (= food limitation) was associated with significant decreases in body size at maturity and increased time to maturity, while FLU had no effect on these traits. Effects of FLU on time to first reproduction, % reproducing females, larvae per brood, broods per female, and population growth rate (λ) varied in response to the intensity of density dependence. In general, interactions between FLU and density were compensatory (antagonistic) at low toxicant exposures, but synergistic at the highest. Population effects are summarised by effects on population growth rate. Our main result is that at low concentrations of FLU (0 to 40 ppm), increasing density alleviated FLU\u27S effects on λ. Thus increasing FLU decreased λ at low density but had no effect at high density. At the highest concentrations of FLU, however, the reverse was the case (\u27synergistic effects\u27). Here, the effect of increasing density is to exacerbate the effects of FLU. This result is particularly important because it demonstrates that LTREs carried out at low density (non-food limited), as most have been in the past, may seriously underestimate effects in the field, where densities are generally high and likely to produce food limitation, as here. Our results suggest that when food availability is limiting, the impact of low levels of toxicant stress on population dynamics may be marginal. By contrast at higher toxicant exposures, food limitation exacerbates toxicant effects and may increase the likelihood of extinction

Effects of chronic fluoranthene exposure on sibling species of \u3ci\u3eCapitella\u3c/i\u3e with different development modes

Toxic effects of the polycyclic aromatic hydrocarbon fluoranthene (FLU) on life-history traits and their demographic consequences were investigated in 3 non-interbreeding Capitella sibling species with different physiological tolerances and developmental modes: sensitive Capitella sp. S from oxygen-rich intertidal sediments of the North Sea (Germany); tolerant Capitella sp. M from sediments near shallow hydrothermal vents off Milos (Greece), a habitat low in organic matter with steep abiotic gradients and high sulfide concentrations; tolerant Capitella sp. I from New York (USA), known to dominate eutrophicated/polluted environments. Both Capitella spp. M and I can develop into hermaphrodites and have lecithotrophic larval development. In contrast, Capitella sp. S appears to be dioecious and has direct development with benthic juveniles. In life-table-response experiments (LTRE), juveniles from the 3 species were raised under different FLU concentrations (0 to 95 μg g–1 FLU), and data on age-specific survival, growth and life-history parameters were recorded at weekly intervals. Under control conditions, the 3 Capitella species differed markedly in a number of life-history traits and population growth rates (λ), with Capitella sp. S showing the lowest λ (1.05), and Capitella sp. M the highest (1.42). Chronic exposure to increasing FLU concentrations also revealed species-specific differences in individual- and population-level toxic responses. Highest FLU concentrations (95 μg g–1) markedly reduced juvenile survival and completely inhibited reproduction in Capitella sp. S, whereas individual life-history traits in Capitella spp. M and I were affected little, if at all. At the population level, the highest FLU exposures resulted in λ values of effectively zero in Capitella sp. S, whereas λ of Capitella spp. M and I remained \u3e1. In conclusion, the combination of opportunistic life-history features, reproductive flexibility, and physiological adaptations enables Capitella spp. M and I to colonize habitats rapidly after local disturbance and to persist in stressed and unpredictable environments; whereas in Capitella sp. S, population extinction under toxicant stress mainly results from its physiological sensitivity