Unlocking the potential of ponds and pondscapes as nature-based solutions for climate resilience and beyond: Hundred evidences.

Unlocking the full potential of ponds (small water bodies) and pondscapes (network of ponds) as Nature-based Solutions (NbS) is critical pursuit for enhancing ecosystems and societal resilience to climate change and other societal challenges. Despite scattered initiatives for pond/pondscape creation, restoration and management-each considered here a distinct NbS-there is a significant knowledge gap in utilising ponds/pondscapes as effective NbS. We aimed to assess these NbS in terms of their objectives, outcomes, effectiveness, multifunctionality, delivery of potentially conflicting effects, and the implementation process while considering their Nature's Contributions to People (NCPs, i.e., benefits to society). We compiled data on 183 NbS actions implemented across 93 ponds/pondscapes from 24 countries, predominantly from Europe, via a questionnaire distributed to experienced stakeholders implementing NbS in ponds/pondscapes. One single pond/pondscape may imply more than one NbS action. Two-thirds were in rural areas, and one-third in urban settings. Our analysis revealed that Creation of habitat for biodiversity was a primary delivery objective (targeted NCP) in the implementation of most NbS in ponds/pondscapes, often also combined with other NCPs such as Learning and inspiration, Regulation of water quantity, and Physical and psychological experiences, showcasing their intended multifunctionality. Implemented NbS primarily focused on climate change adaptation (especially Regulation of hazards and extreme events, and water quantity) rather than mitigation, with less emphasis on measures like direct greenhouse gas emissions reduction or enhancing carbon sinks. The costs associated with pond's NbS varied significantly depending on factors such as project scope, objectives, location, socio-economic-cultural system, and specific implementation requirements. The creation of ponds/pondscapes often entailed the highest financial investment, much more than their restoration or their management. In conclusion, our study underscores the multifunctionality of ponds/pondscapes and provides insights about their significant potential as cost-effective NbS for enhancing ecosystem and societal resilience to climate change and biodiversity. It underscores the importance of further research to fully understand and measure the diverse range of NbS they offer, particularly in the context of climate change mitigation. Standardised measurements of the NCP provided by these NbS in ponds/pondscapes are essential for validating managers' claims and exploring their role in addressing climate change.

Plastic debris in lakes and reservoirs.

Plastic debris is thought to be widespread in freshwater ecosystems globally1. However, a lack of comprehensive and comparable data makes rigorous assessment of its distribution challenging2,3. Here we present a standardized cross-national survey that assesses the abundance and type of plastic debris (>250 µm) in freshwater ecosystems. We sample surface waters of 38 lakes and reservoirs, distributed across gradients of geographical position and limnological attributes, with the aim to identify factors associated with an increased observation of plastics. We find plastic debris in all studied lakes and reservoirs, suggesting that these ecosystems play a key role in the plastic-pollution cycle. Our results indicate that two types of lakes are particularly vulnerable to plastic contamination: lakes and reservoirs in densely populated and urbanized areas and large lakes and reservoirs with elevated deposition areas, long water-retention times and high levels of anthropogenic influence. Plastic concentrations vary widely among lakes; in the most polluted, concentrations reach or even exceed those reported in the subtropical oceanic gyres, marine areas collecting large amounts of debris4. Our findings highlight the importance of including lakes and reservoirs when addressing plastic pollution, in the context of pollution management and for the continued provision of lake ecosystem services.

Genome-phenotype-environment associations identify signatures of selection in a panmictic population of threespine stickleback.

Adaptive genetic divergence occurs when selection imposed by the environment causes the genomic component of the phenotype to differentiate. However, genomic signatures of natural selection are usually identified without information on which trait is responding to selection by which selective agent(s). Here, we integrate whole-genome sequencing with phenomics and measures of putative selective agents to assess the extent of adaptive divergence in threespine stickleback occupying the highly heterogeneous lake Mývatn, NE Iceland. We find negligible genome wide divergence, yet multiple traits (body size, gill raker structure and defence traits) were divergent along known ecological gradients (temperature, predatory bird densities and water depth). SNP based heritability of all measured traits was high (h2  = 0.42-0.65), indicating adaptive potential for all traits. Environment-association analyses further identified thousands of loci putatively involved in selection, related to genes linked to, for instance, neuron development and protein phosphorylation. Finally, we found that loci linked to water depth were concurrently associated with pelvic spine length variation - supporting the conclusion that divergence in pelvic spine length occurred in the face of gene flow. Our results suggest that whilst there is substantial genetic variation in the traits measured, phenotypic divergence of Mývatn stickleback is mostly weakly associated with environmental gradients, potentially as a result of substantial gene flow. Our study illustrates the value of integrative studies that combine genomic assays of multivariate trait variation with landscape genomics.

Individual body mass and length dataset for over 12,000 fish from Iberian streams.

We provide a unique fish individual body size dataset collected from our own sampling and public sources in north-eastern Spain. The dataset includes individual body size measures (fork length and mass) of 12,288 individuals of 24 fish species within 10 families collected at 118 locations in large rivers and small streams. Fish were caught by one-pass electrofishing following European standard protocols. The fish dataset has information on the local instream conditions including climatic variables (i.e., temperature and precipitation), topography (i.e., altitude), nutrient concentration (i.e., total phosphorus and nitrates), and the IMPRESS values (a measure of cumulative human impacts in lotic ecosystems). The potential uses of this new fish dataset are manifold, including developing size-based indices to further estimate the ecological status of freshwater ecosystems, allometric models, and analysis of variation in body size structure along environmental gradients.

Seabird-mediated transport of organohalogen compounds to remote sites (North West Greenland polynya).

The role of sea birds as carriers of pollutants over long distances was evaluated by analyzing organochlorine and organobromine compounds in lake sediment cores from three remote sites around the North Water polynya (North West Greenland). One lake, NOW5, was in the vicinity of a little auk (Alle alle L.) bird colony, whereas the other two lakes, NOW14 and Q5, were undisturbed by seabirds. The former was strongly acidic (pH = 3.4) but the latter had a pH close to 8. Due to the guano loading, NOW5 exhibited higher chlorophyll concentrations (74 µg/L) than the other two lakes (1.6-3.4 µg/L), higher content of total phosphorous (0.34 mg/L vs. 0.007-0.01 mg/L) and total nitrogen (3.75 mg/L vs. 0.21-0.75 mg/L). The concentrations of all organohalogen compounds were substantially greater in NOW5 than in the other lakes, indicating the strong influence of these seabirds in the transport and deposition of these compounds to remote sites. However, not all compounds showed the same increases. Hexachlorocyclohexanes and endosulfans were more than 18 times higher in NOW5, the drin pesticides and hexachlorobenzene (HCB), between 9.5 and 18 times and DDTs, polybromodiphenyl ethers (PBDEs), polychlorobiphenyls (PCBs) and chlordanes about 2.7-6 times. These differences demonstrated that the bird-mediated deposition has preservation effects of the less stable and more volatile compounds, e.g. those with log Kaw < -2.4, log Koa < 9 and/or log Kow < 6.8. The sedimentary fluxes of PCBs, HCHs, drins, chlordanes, PBDEs, HCB and endosulfans were highest in the upper sediment layer of the polynya lake (year 2014). In contrast, the highest DDT fluxes were found in 1980. These trends indicate that despite restrictions and regulations, bird transport continues to introduce considerable amounts of organohalogen pollutants to the Arctic regions with the exception of DDTs, which show successful decline, even when mediated by bird metabolism.

Towards women-inclusive ecology: Representation, behavior, and perception of women at an international conference.

Conferences are ideal platforms for studying gender gaps in science because they are important cultural events that reflect barriers to women in academia. Here, we explored women's participation in ecology conferences by analyzing female representation, behavior, and personal experience at the 1st Meeting of the Iberian Society of Ecology (SIBECOL). The conference had 722 attendees, 576 contributions, and 27 scientific sessions. The gender of attendees and presenters was balanced (48/52% women/men), yet only 29% of the contributions had a woman as last author. Moreover, men presented most of the keynote talks (67%) and convened most of the sessions. Our results also showed that only 32% of the questions were asked by women, yet the number of questions raised by women increased when the speaker or the convener was a woman. Finally, the post-conference survey revealed that attendees had a good experience and did not perceive the event as a threatening context for women. Yet, differences in the responses between genders suggest that women tended to have a worse experience than their male counterparts. Although our results showed clear gender biases, most of the participants of the conference failed to detect it. Overall, we highlight the challenge of increasing women's scientific leadership, visibility and interaction in scientific conferences and we suggest several recommendations for creating inclusive meetings, thereby promoting equal opportunities for all participants.

A systemic overreaction to years versus decades of warming in a subarctic grassland ecosystem.

Temperature governs most biotic processes, yet we know little about how warming affects whole ecosystems. Here we examined the responses of 128 components of a subarctic grassland to either 5-8 or >50 years of soil warming. Warming of >50 years drove the ecosystem to a new steady state possessing a distinct biotic composition and reduced species richness, biomass and soil organic matter. However, the warmed state was preceded by an overreaction to warming, which was related to organism physiology and was evident after 5-8 years. Ignoring this overreaction yielded errors of >100% for 83 variables when predicting their responses to a realistic warming scenario of 1 °C over 50 years, although some, including soil carbon content, remained stable after 5-8 years. This study challenges long-term ecosystem predictions made from short-term observations, and provides a framework for characterization of ecosystem responses to sustained climate change.

Fast attrition of springtail communities by experimental drought and richness-decomposition relationships across Europe.

Soil fauna play a fundamental role on key ecosystem functions like organic matter decomposition, although how local assemblages are responding to climate change and whether these changes may have consequences to ecosystem functioning is less clear. Previous studies have revealed that a continued environmental stress may result in poorer communities by filtering out the most sensitive species. However, these experiments have rarely been applied to climate change factors combining multiyear and multisite standardized field treatments across climatically contrasting regions, which has limited drawing general conclusions. Moreover, other facets of biodiversity, such as functional and phylogenetic diversity, potentially more closely linked to ecosystem functioning, have been largely neglected. Here, we report that the abundance, species richness, phylogenetic diversity, and functional richness of springtails (Subclass Collembola), a major group of fungivores and detritivores, decreased within 4 years of experimental drought across six European shrublands. The loss of phylogenetic and functional richness was higher than expected by the loss of species richness, leading to communities of phylogenetically similar species sharing evolutionary conserved traits. Additionally, despite the great climatic differences among study sites, we found that taxonomic, phylogenetic, and functional richness of springtail communities alone were able to explain up to 30% of the variation in annual decomposition rates. Altogether, our results suggest that the forecasted reductions in precipitation associated with climate change may erode springtail communities and likely other drought-sensitive soil invertebrates, thereby retarding litter decomposition and nutrient cycling in ecosystems.

Short-term fish predation destroys resilience of zooplankton communities and prevents recovery of phytoplankton control by zooplankton grazing.

Planktivorous fish predation directly affects zooplankton biomass, community and size structure, and may indirectly induce a trophic cascade to phytoplankton. However, it is not clear how quickly the zooplankton community structure and the cascading effects on phytoplankton recover to the unaffected state (i.e. resilience) once short-term predation by fish stops. The resilience has implications for the ecological quality and restoration measures in aquatic ecosystems. To assess the short-term zooplankton resilience against fish predation, we conducted a mesocosm experiment consisting of 10 enclosures, 6 with fish and 4 without fish. Plankton communities from a natural lake were used to establish phytoplankton and zooplankton in the mesocosms. High biomasses (about 20 g wet mass m-3) of juvenile planktivorous fish (perch, Perca fluviatilis) were allowed to feed on zooplankton in fish enclosures for four days. Thereafter, we removed fish and observed the recovery of the zooplankton community and its cascading effect on trophic interactions in comparison with no fish enclosures for four weeks. Short-term fish predation impaired resilience in zooplankton community by modifying community composition, as large zooplankton, such as calanoids, decreased just after fish predation and did not re-appear afterwards, whereas small cladocerans and rotifers proliferated. Total zooplankton biomass increased quickly within two weeks after fish removal, and at the end even exceeded the biomass measured before fish addition. Despite high biomass, the dominance of small zooplankton released phytoplankton from grazer control in fish enclosures. Accordingly, the zooplankton community did not recover from the effect of fish predation, indicating low short-term resilience. In contrast, in no fish enclosures without predation disturbance, a high zooplankton:phytoplankton biomass ratio accompanied by low phytoplankton yield (Chlorophyll-a:Total phosphorus ratio) reflected phytoplankton control by zooplankton over the experimental period. Comprehensive views on short and long-term resilience of zooplankton communities are essential for restoration and management strategies of aquatic ecosystems to better predict responses to global warming, such as higher densities of planktivorous fish.

Impact of Soil Warming on the Plant Metabolome of Icelandic Grasslands.

Climate change is stronger at high than at temperate and tropical latitudes. The natural geothermal conditions in southern Iceland provide an opportunity to study the impact of warming on plants, because of the geothermal bedrock channels that induce stable gradients of soil temperature. We studied two valleys, one where such gradients have been present for centuries (long-term treatment), and another where new gradients were created in 2008 after a shallow crustal earthquake (short-term treatment). We studied the impact of soil warming (0 to +15 °C) on the foliar metabolomes of two common plant species of high northern latitudes: Agrostis capillaris, a monocotyledon grass; and Ranunculus acris, a dicotyledonous herb, and evaluated the dependence of shifts in their metabolomes on the length of the warming treatment. The two species responded differently to warming, depending on the length of exposure. The grass metabolome clearly shifted at the site of long-term warming, but the herb metabolome did not. The main up-regulated compounds at the highest temperatures at the long-term site were saccharides and amino acids, both involved in heat-shock metabolic pathways. Moreover, some secondary metabolites, such as phenolic acids and terpenes, associated with a wide array of stresses, were also up-regulated. Most current climatic models predict an increase in annual average temperature between 2-8 °C over land masses in the Arctic towards the end of this century. The metabolomes of A. capillaris and R. acris shifted abruptly and nonlinearly to soil warming >5 °C above the control temperature for the coming decades. These results thus suggest that a slight warming increase may not imply substantial changes in plant function, but if the temperature rises more than 5 °C, warming may end up triggering metabolic pathways associated with heat stress in some plant species currently dominant in this region.

Pharmaceuticals and Personal-Care Products in Plants.

Pharmaceuticals and personal-care products (PPCPs) derived from agricultural, urban, and industrial areas accumulate in plants at concentrations (ng to µg kg-1) that can be toxic to the plants. Importantly, the dietary intake of these PPCP-contaminated plants may also pose a risk to human health, but currently little is known about the fate of PPCPs in plants and their effect on or risk to the ecosystem. In this Opinion article we propose that in-depth research on the use of plants as a monitoring device for assessing the use and environmental presence of PPCPs is warranted. The toxicity of PPCPs to plants and their microbiota needs to be established, as well as any toxic effects on herbivores including humans.

Plant invasion is associated with higher plant-soil nutrient concentrations in nutrient-poor environments.

Plant invasion is an emerging driver of global change worldwide. We aimed to disentangle its impacts on plant-soil nutrient concentrations. We conducted a meta-analysis of 215 peer-reviewed articles and 1233 observations. Invasive plant species had globally higher N and P concentrations in photosynthetic tissues but not in foliar litter, in comparison with their native competitors. Invasive plants were also associated with higher soil C and N stocks and N, P, and K availabilities. The differences in N and P concentrations in photosynthetic tissues and in soil total C and N, soil N, P, and K availabilities between invasive and native species decreased when the environment was richer in nutrient resources. The results thus suggested higher nutrient resorption efficiencies in invasive than in native species in nutrient-poor environments. There were differences in soil total N concentrations but not in total P concentrations, indicating that the differences associated to invasive plants were related with biological processes, not with geochemical processes. The results suggest that invasiveness is not only a driver of changes in ecosystem species composition but that it is also associated with significant changes in plant-soil elemental composition and stoichiometry.

Spatial And Temporal Trends Of Organic Pollutants In Vegetation From Remote And Rural Areas.

Persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) used in agricultural, industrial, and domestic applications are widely distributed and bioaccumulate in food webs, causing adverse effects to the biosphere. A review of published data for 1977-2015 for a wide range of vegetation around the globe indicates an extensive load of pollutants in vegetation. On a global perspective, the accumulation of POPs and PAHs in vegetation depends on the industrialization history across continents and distance to emission sources, beyond organism type and climatic variables. International regulations initially reduced the concentrations of POPs in vegetation in rural areas, but concentrations of HCB, HCHs, and DDTs at remote sites did not decrease or even increased over time, pointing to a remobilization of POPs from source areas to remote sites. The concentrations of compounds currently in use, PBDEs and PAHs, are still increasing in vegetation. Differential congener specific accumulation is mostly determined by continent-in accordance to the different regulations of HCHs, PCBs and PBDEs in different countries-and by plant type (PAHs). These results support a concerning general accumulation of toxic pollutants in most ecosystems of the globe that for some compounds is still far from being mitigated in the near future.

Taking the trophic bypass: aquatic-terrestrial linkage reduces methylmercury in a terrestrial food web.

Ecosystems can be linked by the movement of matter and nutrients across habitat boundaries via aquatic insect emergence. Aquatic organisms tend to have higher concentrations of certain toxic contaminants such as methylmercury (MeHg) compared to their terrestrial counterparts. If aquatic organisms come to land, terrestrial organisms that consume them are expected to have elevated MeHg concentrations. But emergent aquatic insects could have other impacts as well, such as altering consumer trophic position or increasing ecosystem productivity as a result of nutrient inputs from insect carcasses. We measure MeHg in terrestrial arthropods at two lakes in northeastern Iceland and use carbon and nitrogen stable isotopes to quantify aquatic reliance and trophic position. Across all terrestrial focal arthropod taxa (Lycosidae, Linyphiidae, Acari, Opiliones), aquatic reliance had significant direct and indirect (via changes in trophic position) effects on terrestrial consumer MeHg. However, contrary to our expectations, terrestrial consumers that consumed aquatic prey had lower MeHg concentrations than consumers that ate mostly terrestrial prey. We hypothesize that this is due to the lower trophic position of consumers feeding directly on midges relative to those that fed mostly on terrestrial prey and that had, on average, higher trophic positions. Thus, direct consumption of aquatic inputs results in a trophic bypass that creates a shorter terrestrial food web and reduced biomagnification of MeHg across the food web. Our finding that MeHg was lower at terrestrial sites with aquatic inputs runs counter to the conventional wisdom that aquatic systems are a source of MeHg contamination to surrounding terrestrial ecosystems.

Sensing the energetic status of plants and ecosystems.

The emerging consistency of the relationship between biochemical, optical, and odorous signals emitted by plants and ecosystems offers promising prospects for continuous local and global monitoring of the energetic status of plants and ecosystems, and therefore of their processing of energy and matter.

Global biodiversity, stoichiometry and ecosystem function responses to human-induced C-N-P imbalances.

Global change analyses usually consider biodiversity as a global asset that needs to be preserved. Biodiversity is frequently analysed mainly as a response variable affected by diverse environmental drivers. However, recent studies highlight that gradients of biodiversity are associated with gradual changes in the distribution of key dominant functional groups characterized by distinctive traits and stoichiometry, which in turn often define the rates of ecosystem processes and nutrient cycling. Moreover, pervasive links have been reported between biodiversity, food web structure, ecosystem function and species stoichiometry. Here we review current global stoichiometric gradients and how future distributional shifts in key functional groups may in turn influence basic ecosystem functions (production, nutrient cycling, decomposition) and therefore could exert a feedback effect on stoichiometric gradients. The C-N-P stoichiometry of most primary producers (phytoplankton, algae, plants) has been linked to functional trait continua (i.e. to major axes of phenotypic variation observed in inter-specific analyses of multiple traits). In contrast, the C-N-P stoichiometry of higher-level consumers remains less precisely quantified in many taxonomic groups. We show that significant links are observed between trait continua across trophic levels. In spite of recent advances, the future reciprocal feedbacks between key functional groups, biodiversity and ecosystem functions remain largely uncertain. The reported evidence, however, highlights the key role of stoichiometric traits and suggests the need of a progressive shift towards an ecosystemic and stoichiometric perspective in global biodiversity analyses.

Nitrogen-cycling genes in epilithic biofilms of oligotrophic high-altitude lakes (central Pyrenees, Spain).

Microbial biofilms in oligotrophic environments are the most reactive component of the ecosystem. In high-altitude lakes, exposed bedrock, boulders, gravel, and sand in contact with highly oxygenated water and where a very thin epilithic biofilm develops usually dominate the littoral zone. Traditionally, these surfaces have been considered unsuitable for denitrification, but recent investigations have shown higher biological diversity than expected, including diverse anaerobic microorganisms. In this study, we explored the presence of microbial N-cycling nirS and nirK (denitrification through the conversion of NO2(-) to NO), nifH (N2 fixation), anammox (anaerobic ammonium oxidation), and amoA (aerobic ammonia oxidation, both bacterial and archaeal) genes in epilithic biofilms of a set of high-altitude oligotrophic lakes in the Pyrenees. The concentrations of denitrifying genes determined by quantitative PCR were two orders of magnitude higher than those of ammonia-oxidizing genes. Both types of genes were significantly correlated, suggesting a potential tight coupling nitrification-denitrification in these biofilms that deserves further confirmation. The nifH gene was detected after nested PCR, and no signal was detected for the anammox-specific genes used. The taxonomic composition of denitrifying and nitrogen-fixing genes was further explored by cloning and sequencing. Interestingly, both microbial functional groups were richer and more genetically diverse than expected. The nirK gene, mostly related to Alphaproteobacteria (Bradyrhizobiaceae), dominated the denitrifying gene pool as expected for oxygen-exposed habitats, whereas Deltaproteobacteria (Geobacter like) and Cyanobacteria were the most abundant among nitrogen fixers. Overall, these results suggest an epilithic community more metabolically diverse than previously thought and with the potential to carry out an active role in the biogeochemical nitrogen cycling of high-altitude ecosystems. Measurements of activity rates should be however carried out to substantiate and further explore these findings.

Missing effects of anthropogenic nutrient deposition on sentinel alpine ecosystems.

Anthropogenic nitrogen (N) deposition affects unproductive remote alpine and circumpolar ecosystems, which are often considered sentinels of global change. Human activities and forest fires can also elevate phosphorus (P) deposition, possibly compounding the ecological effects of increased N deposition given the ubiquity of nutrient co-limitation of primary producers. Low N : P ratios coupled with evidence of NP-limitation from bioassays led us to hypothesize that P indirectly stimulates phytoplankton by amplifying the direct positive effect of N (i.e. serial N-limitation) in alpine ponds. We tested the hypothesis using the first replicated N × P enrichment experiment conducted at the whole-ecosystem level, which involved 12 alpine ponds located in the low N deposition backcountry of the eastern Front Range of the Canadian Rockies. Although applications of N and P elevated ambient N and P concentrations by 2-5×, seston and plankton remained relatively unaffected in the amended ponds. However, additions of ammonium nitrate elevated the δ(15) N signals of both primary producers and herbivores (fairy shrimp; Anostraca), attesting to trophic transfer of N deposition to consumers. Further, in situ bioassays revealed that grazing by high ambient densities of fairy shrimp together with potential competition from algae lining the pond bottoms suppressed the otherwise serially N-limited response by phytoplankton. Our findings highlight how indirect effects of biotic interactions rather the often implicit direct effects of chemical changes can regulate the sensitivities of extreme ecosystems to nutrient deposition.

Pollutant dehalogenation capability may depend on the trophic evolutionary history of the organism: PBDEs in freshwater food webs.

Organohalogen compounds are some of the most notorious persistent pollutants disturbing the Earth biosphere. Although human-made, these chemicals are not completely alien to living systems. A large number of natural organohalogens, part of the secondary metabolism, are involved in chemical trophic interactions. Surprisingly, the relationship between organisms' trophic position and synthetic organohalogen biotransformation capability has not been investigated. We studied the case for polybromodiphenyl ethers (PBDE), a group of flame-retardants of widespread use in the recent years, in aquatic food webs from remote mountain lakes. These relatively simple ecosystems only receive pollution by atmospheric transport. A large predominance of the PBDE congener currently in use in Europe, BDE-209, largely dominated the PBDE composition of the basal resources of the food web. In contrast, primary consumers (herbivores and detritivores) showed a low proportion of BDE-209, and dominance of several less brominated congeners (e.g. BDE-100, BDE47). Secondary consumers (predators) showed large biomagnification of BDE-209 compare to other congeners. Finally, top predator fish characterized by low total PBDE concentrations. Examination of the bromine stable isotopic composition indicates that primary consumers showed higher PBDE biotransformation capability than secondary consumers. We suggest that the evolutionary response of primary consumers to feeding deterrents would have pre-adapted them for PBDE biotransformation. The observed few exceptions, some insect taxa, can be interpreted in the light of the trophic history of the evolutionary lineage of the organisms. Bromine isotopic composition in fish indicates that low PBDE values are due to not only biotransformation but also to some other process likely related to transport. Our finding illustrates that organohalogen compounds may strongly disturb ecosystems even at low concentrations, since the species lacking or having scarce biotransformation capability may be selectively more exposed to these halogenated hydrophobic semi-volatile organic pollutants due to their high bioaccumulation potential.