Special challenges in the conservation of fishes and aquatic environments of South America

Mercury concentrations and stable isotopes (δ15N and δ13C) in fish muscle indicate human impacts in tropical coastal lagoons

Coastal lagoons are essential nursery habitats of many marine fishes, but they are often sites of intense human activities that impact water quality and potentially the fish using these habitats. We compared the variability in nutrient uptake (using δ¹⁵N and δ¹³C) and total mercury (THg) levels in juveniles and adults of three common species in two lagoons on the central Mexican coast of the Pacific Ocean during the wet and dry seasons. One of three species, Achirus mazatlanus had higher THg, δ¹⁵N, and δ¹³C levels in the lagoon with the greatest wastewater inputs (Barra de Navidad). Delta¹³C varied seasonally for all three species and THg was higher in the dry season for Lutjanus argentiventris and in males of A. mazatlanus. Our results demonstrate that mercury and stable isotopes can identify impacts of human activities on estuarine ichthyofauna and the importance of understanding seasonal and spatial variability of measures that could impact monitoring and predictions of impacts in these lagoons.

Water, sediments and fishes: First multi compartment assessment of metal pollution in a coastal environment from the SW Atlantic

This is an integrated assessment of the distribution of Cd, Cr, Hg and Pb in dissolved water, sediments and muscle fish tissues (Cynoscion guatucupa, Micropogonias furnieri, Mustelus schmitti and Ramnogaster arcuata) from the Bahía Blanca estuary, Argentina. Within the water fraction (μg L^-1), Hg and Pb concentrations ranged from below the limit of detection (<LOD) to 0.53 and 54, respectively. For Cd and Cr, values varied from 0.060 to 0.56 and from 1.6 to 18, respectively. In the sediment fraction (μg g^-1) values ranged from <LOD to 0.21 and 0.47 for Cd and Hg, respectively, from 11 to 18 for Cr and from 5.1 to 10 for Pb. Metals in fish muscle tissues (μg g^-1) ranged from <LOD to 2.8, 0.53 and 0.52 for Cr, Hg and Pb, respectively. All Cd values were <LOD. This marine environment is potentially vulnerable to anthropogenic pollution since dissolved Cr, Hg and Pb values exceeded established environmental quality guidelines. Moreover, the sediment pollution indices indicated a deterioration of the estuarine environment, with Cr and Pb associated to anthropogenic impacts, whereas Hg could be occasionally associated with adverse biological effects. The biota to water accumulation factor (BWAF) reflected that fish species showed potential to accumulate Cr (BWAF: 73-510) and, especially, Hg (BWAF: 1000-8000). The high biota to sediment accumulation factor found for Hg (up to 9.8) indicated that fish species behaved as macro or micro concentrators. These results highlights the importance of a multi compartment approach in pollution assessment, with implicances for future works.

Use of complex physiological traits as ecotoxicological biomarkers in tropical freshwater fishes

We review the use of complex physiological traits, of tolerance and performance, as biomarkers of the toxicological effects of contaminants in subtropical and tropical freshwater fishes. Such traits are growing in relevance due to climate change, as exposure to contaminants may influence the capacity of fishes to tolerate and perform in an increasingly stressful environment. We review the evidence that the critical oxygen level, a measure of hypoxia tolerance, provides a valuable biomarker of impacts of diverse classes of contaminants. When coupled with measures of cardiorespiratory variables, it can provide insight into mechanisms of toxicity. The critical thermal maximum, a simple measure of tolerance of acute warming, also provides a valuable biomarker despite a lack of understanding of its mechanistic basis. Its relative ease of application renders it useful in the rapid evaluation of multiple species, and in understanding how the severity of contaminant impacts depends upon prevailing environmental temperature. The critical swimming speed is a measure of exercise performance that is widely used as a biomarker in temperate species but very few studies have been performed on subtropical or tropical fishes. Overall, the review serves to highlight a critical lack of knowledge for subtropical and tropical freshwater fishes. There is a real need to expand the knowledge base and to use physiological biomarkers in support of decision making to manage tropical freshwater fish populations and their habitats, which sustain rich biodiversity but are under relentless anthropogenic pressure.

Cardiac and behavioural responses to hypoxia and warming in free-swimming gilthead seabream, Sparus aurata

Gilthead seabream were equipped with intraperitoneal biologging tags to investigate cardiac responses to hypoxia and warming, comparing when fish were either swimming freely in a tank with conspecifics or confined to individual respirometers. After tag implantation under anaesthesia, heart rate (fH) required 60 h to recover to a stable value in a holding tank. Subsequently, when undisturbed under control conditions (normoxia, 21°C), mean fH was always significantly lower in the tank than in the respirometers. In progressive hypoxia (100% to 15% oxygen saturation), mean fH in the tank was significantly lower than in the respirometers at oxygen levels down to 40%, with significant bradycardia in both holding conditions below this level. Simultaneous logging of tri-axial body acceleration revealed that spontaneous activity, inferred as the variance of external acceleration (VARm), was low and invariant in hypoxia. Warming (21 to 31°C) caused progressive tachycardia with no differences in fH between holding conditions. Mean VARm was, however, significantly higher in the tank during warming, with a positive relationship between VARm and fH across all temperatures. Therefore, spontaneous activity contributed to raising fH of fish in the tank during warming. Mean fH in respirometers had a highly significant linear relationship with mean rates of oxygen uptake, considering data from hypoxia and warming together. The high fH of confined seabream indicates that respirometry techniques may bias estimates of metabolic traits in some fishes, and that biologging on free-swimming fish will provide more reliable insight into cardiac and behavioural responses to environmental stressors by fish in their natural environment.

Occurrence of microplastics and heavy metals accumulation in native oysters Crassostrea Gasar in the Paranaguá estuarine system, Brazil

The ubiquitous presence of contaminants in the marine environment is considered a global threat to marine organisms. Heavy metals and microplastics are two distinct classes of pollutants but there are interactions between these two stressors that are still poorly understood. We examined the potential relationship between heavy metals (Al, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Ba, Hg, Pb) and microplastic particles in oysters sampled along the Paranaguá Estuarine System. The results suggested high levels of As and Zn in the bivalves, which are destined for human consumption. Microplastic particles were found in oysters from all sampled locations, demonstrating the spread of this pollutant in the marine environment and its ability to bioaccumulate in oysters. However, our data did not demonstrate a direct relationship between microplastics and heavy metals, suggesting that these particles are not the main route for heavy metal contamination of oysters in the Paranaguá Estuarine System.

Human impacts and the loss of Neotropical freshwater fish diversity

Abstract Neotropical Ichthyology promotes the Special Issue (SI) “Human impacts and the loss of Neotropical freshwater fish diversity” with the purpose of publishing relevant scientific articles on the current biodiversity crisis and the loss of Neotropical freshwater fishes in the Anthropocene. The SI is composed of 22 publications, being two review articles and 20 original articles. A total of 107 researchers contributed to these papers, involving 44 institutions based in Brazil and six other countries. Published articles investigated main anthropic activities and their impacts on fish diversity, with special focus on river regulation, mining, land use changes, aquaculture, and fisheries. Studies provided evidence about the loss of fish diversity in the Neotropics, including fish kill events, demographic changes, contamination, changes in assemblage structure, loss of taxonomic and functional diversity, besides the degradation of ecosystem functions and services, and the lack of effective protection and conservation. Studies were conducted in rivers, streams, lakes, and reservoirs from different Neotropical systems. The studies published in this SI represent a relevant sample of the current worrisome situation of freshwater fishes in the Neotropical region and call for urgent revision in environmental policies, management and conservation initiatives, and socioeconomic priorities.

Gathering at the top? Environmental controls of microplastic uptake and biomagnification in freshwater food webs

Microplastics are ubiquitous in the environment, with high concentrations being detected now also in river corridors and sediments globally. Whilst there has been increasing field evidence of microplastics accumulation in the guts and tissues of freshwater and marine aquatic species, the uptake mechanisms of microplastics into freshwater food webs, and the physical and geological controls on pathway-specific exposures to microplastics, are not well understood. This knowledge gap is hampering the assessment of exposure risks, and potential ecotoxicological and public health impacts from microplastics. This review provides a comprehensive synthesis of key research challenges in analysing the environmental fate and transport of microplastics in freshwater ecosystems, including the identification of hydrological, sedimentological and particle property controls on microplastic accumulation in aquatic ecosystems. This mechanistic analysis outlines the dominant pathways for exposure to microplastics in freshwater ecosystems and identifies potentially critical uptake mechanisms and entry pathways for microplastics and associated contaminants into aquatic food webs as well as their risk to accumulate and biomagnify. We identify seven key research challenges that, if overcome, will permit the advancement beyond current conceptual limitations and provide the mechanistic process understanding required to assess microplastic exposure, uptake, hazard, and overall risk to aquatic systems and humans, and provide key insights into the priority impact pathways in freshwater ecosystems to support environmental management decision making.

Plastic pollution in the marine environment

Plastic pollution is recognized as a severe anthropogenic issue in the coastal and marine ecosystems across the world. Unprecedented and continuous accumulation of growing plastic contaminants into any respective aquatic ecosystem by the anthropogenic sources causes direct and/or indirect interruption to ecosystem structure, functions, and consequently, services and values. Land-based and sea-based sources are the primary sources of these contaminants in various modes that enter the ocean. In this review paper, we focused on highlighting different aspects related to plastic pollution in coastal and marine environments. Plastic pollutants are distributed in the ecosystems in different forms, with different size variations as megaplastic, macroplastic, mesoplastic, and microplastic. Microplastics in primary and secondary forms reveal a widespread distribution in the water, sediment, and biota of the marine and coastal habitats. The microplastic level of different coastal and marine ecosystems nearly ranged from 0.001-140 particles/m3 in water and 0.2-8766 particles/m3 in sediments at different aquatic environments over the world. The microplastic accumulation rate of coastal and marine organisms varied at 0.1-15,033 counts. Accordingly, plastic pollution creates several kinds of negative consequences combined with ecological and socio-economic effects. Entanglement, toxicological effects via ingestion of plastics, suffocation, starvation, dispersal, and rafting of organisms, provision of new habitats, and introduction of invasive species are significant ecological effects with growing threats to biodiversity and trophic relationships. Degradation (changes in the ecosystem state) and modifications of marine systems are associated with loss of ecosystem services and values. Consequently, this emerging contaminant affects the socio-economic aspects through negative impacts on tourism, fishery, shipping, and human health. Preventing accumulation sources of plastic pollutants, 3Rs (Reduce-Recycle-Reuse), awareness & capacity building, and producer/manufacturer responsibility are practical approaches toward addressing the issue of plastic pollution. Existing and adopted policies, legislations, regulations, and initiatives at global, regional, and national level play a vital role in reducing plastic debris in the marine and coastal zones. Development of proposals/solutions on key research gaps can open a novel pathway to address this environmental issue in an effective scientific manner. In conclusion, this paper demonstrates the current status of plastic pollution in the marine ecosystem to make aware people of a plastic-free, healthy blue ocean in the near future.

Anthropogenic litter on Brazilian beaches: Baseline, trends and recommendations for future approaches

Beaches are fundamental habitats that regulate the functioning of several coastal processes and key areas contributing to national and local budgets. In this study we provide the first large-scale systematic survey of anthropogenic litter on Brazilian beaches, covering a total of 35 degrees of latitude, recording the litter type, its use and size. Plastic comprised the most abundant litter type, followed by cigarette butts and paper. Small pieces (<5 cm) were dominant among litter size-classes and food-related use was associated to most litter recorded types. Generalized additive models showed that proximity to estuarine run-offs was the main driver to beach litter accumulation, reinforcing river drainages as the primary route of litter coastal pollution. Also, the Clean-Coast Index evidenced there was not a pattern of beach litter pollution among regions, which denotes that actions regarding marine pollution must be taken by all state governances of the country.

Distribution, sources and consequences of nutrients, persistent organic pollutants, metals and microplastics in South American estuaries

Estuarine pollution imposes rapid, increasing and lasting environmental modifications. In the present review, especial attention is given to estuaries in South America (SA), where legislation, policies and actions to guarantee environmental quality remain ineffective. There, the majority of estuaries face uncontrolled occupation of its margins by urban and industrial centres, agriculture and aquaculture expansion, water extraction and flow control. The lack of basic sanitation and poor environmental management (including territories within Marine Protected Areas) often lead to hydrological alterations, high nutrient loads, and the presence and dynamics of pollutants (nutrient loads, persistent organic pollutants (POPs), metals and plastic debris) along the entire estuarine ecocline. Organic enrichment has increased dissolved oxygen consumption, with wide spatio-temporal variability along latitudes and estuarine gradients. The toxicity, biogeochemistry and availability of metals and POPs depend on the annual fluctuations of salinity, water renewal, dissolved oxygen levels, suspended particulate loads, sediment mobility, grain size and composition at the sink. Plastic debris from land sources are widespread in estuaries, where they continue to fragment into microplastics. River basins are the main contributors of plastics to estuaries, whose transportation and accumulation are subjected to interannual water flow variations. Although some systems seems to be in a better condition in relation to others around the world (e.g. Goiana and Negro estuaries), many others are among the most modified worldwide (e.g. Guanabara Bay and Estero Salado System). We propose that, estuarine conservation plans should consider year-round fluctuations of the ecocline and the resulting cycles of retention and flush of environmental signals and their influence on trophic webs over the whole extent of estuarine gradients.