Indirect effects in aquatic ecosystems

Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
Science of The Total Environment (Impact Factor: 4.1). 01/2004; 317(1-3):207-33. DOI: 10.1016/S0048-9697(03)00141-4
Source: PubMed


Contaminants such as petroleum hydrocarbons, heavy metals and pesticides can cause direct toxic effects when released into aquatic environments. Sensitive species may be impaired by sublethal effects or decimated by lethality, and this ecological alteration may initiate a trophic cascade or a release from competition that secondarily leads to responses in tolerant species. Contaminants may exert direct effects on keystone facilitator and foundation species, and contaminant-induced changes in nutrient and oxygen dynamics may alter ecosystem function. Thus, populations and communities in nature may be directly and/or indirectly affected by exposure to pollutants. While the direct effects of toxicants usually reduce organism abundance, indirect effects may lead to increased or decreased abundance. Here we review 150 papers that reference indirect toxicant effects in aquatic environments. Studies of accidental contaminant release, chronic contamination and experimental manipulations have identified indirect contaminant effects in pelagic and benthic communities caused by many types of pollutants. Contaminant-induced changes in behavior, competition and predation/grazing rate can alter species abundances or community composition, and enhance, mask or spuriously indicate direct contaminant effects. Trophic cascades were found in 60% of the manipulative studies and, most commonly, primary producers increased in abundance when grazers were selectively eliminated by contaminants. Competitive release may also be common, but is difficult to distinguish from trophic cascades because few experiments are designed to isolate the mechanism(s) causing indirect effects. Indirect contaminant effects may have profound implications in environments with strong trophic cascades such as the freshwater pelagic. In spite of their undesirable environmental influence, contaminants can be useful manipulative tools for the study of trophic and competitive interactions in natural communities.

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    • "Estuarine and rocky intertidal organisms are particularly at risk from pharmaceuticals as environmental stressors (Fong and Ford, 2014), however data from prolonged studies in these ecosystems are lacking (Gaw et al., 2014). Exposure to heavy metals, pesticides, petroleum and other legacy contaminants have been shown to affect marine organisms by altering habitat preference, shifting migration patterns, or increasing negative species interactions (Fleeger et al., 2003; Banni et al., 2007; Fukunaga et al., 2010). Such alterations to normal behaviors have been linked to reduced fitness, and changes to population structure and ecosystem function (Frid and Dill, 2002; Fahrig, 2007). "
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    ABSTRACT: Environmental stressors shape community composition and ecosystem functioning. Contaminants such as pharmaceuticals are of increasing concern as an environmental stressor due to their persistence in surface waters worldwide. Limited attention has been paid to the effects of pharmaceuticals on marine life, despite widespread detection of these contaminants in the marine environment. Of the existing studies, the majority assess the negative effects of pharmaceuticals over an exposure period of 30 days or less and focus on cellular and subcellular biomarkers. Longer studies are required to determine if chronic contaminant exposure poses risks to marine life at environmentally relevant concentrations; and examination of whole organism effects are necessary to identify potential community-level consequences in estuarine and marine ecosystems. We conducted a long-term expo-sure study (107 days) with the anti-depressant pharmaceutical,fluoxetine (the active constituent in Prozac®) to determine whether minimal concentrations affected whole organism metrics in the California mussel, Mytilus californianus. We measured algal clearance rates, mussel growth, and the gonadosomatic index, a measure of re-productive health. We found that fluoxetine negatively affects all measured characteristics, however many effects were mediated by length of exposure. Our results fill an important data gap, highlighting organism-level effects of chronic exposure periods; such data more explicitly identify the overall impacts of pharmaceuticals and other contaminants on marine communities and ecosystems. Long-term exposure to fluoxetine reduces growth and reproductive potential in the dominant rocky intertidal mussel, Mytilus californianus. Available from: [accessed Jan 7, 2016].
    Full-text · Article · May 2016 · Science of The Total Environment
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    • "However, also chronic direct effects and acute and chronic sublethal toxic effects can lead to changes in invertebrate communities through reduced reproduction or predator avoidance. Likewise, effects on other groups of organisms such as primary producers that were not included in our study may propagate to invertebrate consumers (Fleeger et al., 2003). "
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    ABSTRACT: The European Union aims to reach a 10% share of biofuels in the transport sector by 2020. The major burden is most likely to fall on already established annual energy crops such as rapeseed and cereals for the production of biodiesel and bioethanol, respectively. Annual energy crops are typically cultivated in intensive agricultural production systems, which require the application of pesticides. Agricultural pesticides can have adverse effects on aquatic invertebrates in adjacent streams. We assessed the relative ecological risk to aquatic invertebrates associated with the chemical pest management from six energy crops (maize, potato, sugar beet, winter barley, winter rapeseed, and winter wheat) as well as from mixed cultivation scenarios. The pesticide exposure related to energy crops and cultivation scenarios was estimated as surface runoff for 253 small stream sites in Central Germany using a GIS-based runoff potential model. The ecological risk for aquatic invertebrates, an important organism group for the functioning of stream ecosystems, was assessed using acute toxicity data (48-h LC50 values) of the crustacean Daphnia magna. We calculated the Ecological Risk from potential Pesticide Runoff (ERPR) for all three main groups of pesticides (herbicides, fungicides, and insecticides). Our findings suggest that the crops potato, sugar beet, and rapeseed pose a higher ecological risk to aquatic invertebrates than maize, barley, and wheat. As maize had by far the lowest ERPR values, from the perspective of pesticide pollution, its cultivation as substrate for the production of the gaseous biofuel biomethane may be preferable compared to the production of, for example, biodiesel from rapeseed.
    Full-text · Article · Dec 2015 · Science of The Total Environment
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    • "Heavy metals are an important category of pollutants and as such have major detrimental impacts on both human health (Duruibe et al. 2007) and the health of terrestrial and aquatic communities and ecosystems (Sánchez 2008). In addition to direct effects, these pollutants may have indirect effects through their impact on the structure of food webs (Fleeger et al. 2003). Alkaline precipitation, ion exchange columns, electrochemical removal, filtration, and membrane technologies are the currently used for heavy metal removal. "
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    ABSTRACT: Heavy metals have detrimental impacts on the health of organisms including human beings. Wetlands are economical, natural alternatives for the removal of heavy metals from the environment and macrophytes play a pivotal role in this direction, though they vary in their potential to do so. Heavy metal accumulation capability of two dominant species (Ceratophyllum demersum and Potamogeton natans) in a Kashmir Himalayan Ramsar site was studied. The accumulation of the different metals in P. natans was in the order of Al > Mn > Pb > Cu > Zn > Ni > Co > Cr > Cd, while in C. demersum it was Al > Mn > Zn > Co > Cu > Pb > Cr > Ni > Cd. In C. demersum the highest bioconcentration factor (BCF) was obtained for Co (3616) and Mn (3589) while in P. natans the highest BCF corresponded to Cd (1027). Overall Potamogeton–Ceratophyllum combination may provide a useful mix for Co, Mn and Cd removal from contaminated sites. The management implications of these results are briefly discussed.
    Full-text · Article · Dec 2015 · Wetlands Ecology and Management
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