Ecological and socio‐economic impacts of invasive water hyacinth (Eichhornia crassipes): a review

1. Water hyacinth (Eichhornia crassipes) is one of the world’s most invasive aquatic plants and is known to cause significant ecological and socio‐economic effects. 2. Water hyacinth can alter water clarity and decrease phytoplankton production, dissolved oxygen, nitrogen, phosphorous, heavy metals and concentrations of other contaminants. 3. The effects of water hyacinth on ecological communities appear to be largely nonlinear. Abundance and diversity of aquatic invertebrates generally increase in response to increased habitat heterogeneity and structural complexity provided by water hyacinth but decrease due to decreased phytoplankton (food) availability. 4. Effects of water hyacinth on fish are largely dependent on original community composition and food‐web structure. A more diverse and abundant epiphytic invertebrate community may increase fish abundance and diversity, but a decrease in phytoplankton may decrease dissolved oxygen concentrations and planktivorous fish abundance, subsequently affecting higher trophic levels. 5. Little is known about the effects of water hyacinth on waterbird communities; however, increases in macroinvertebrate and fish abundance and diversity suggest a potentially positive interaction with waterbirds when water hyacinth is at moderate density. 6. The socio‐economic effects of water hyacinth are dependent on the extent of the invasion, the uses of the impacted waterbody, control methods and the response to control efforts. Ecosystem‐level research programmes that simultaneously monitor the effects of water hyacinth on multiple trophic‐levels are needed to further our understanding of invasive species.     

Bioaccumulation of heavy metals in the different tissues of Mackerel scad,Decapterus macarellus (Cuvier, 1833) collected from Karachi and Gwadar Coasts of Pakistan

IntroductionAmong other aquatic animals, fish can also accumulate a large number of toxic metals in their various body organs, which may enter in the human body and cause serious health issues. Therefore, the basic aim of this study was to observe the level of some heavy metals (i.e., Pb, Fe, Cu, Cd, Cr) found in the different tissues of Decapterus macarellus collected from the Karachi and Gwadar coasts of Pakistan.MethodsAbout 200 fish samples of five different size groups of Decapterus macarellus were collected from Gwadar and Karachi fish harbors during April to September 2020. Total 10 samples of each size group i.e., S1, S2, S3, S4 & S5 were collected from each coast. Heavy metals were analyzed in fish samples by using the atomic absorption spectrophotometer (AAS).ResultsThe overall results revealed that some metals like Cu, Pb, Cd & Cr contents were high in the stomach, while less in the muscles. Whereas, the concentration of Fe was found to be high in the liver, while low in skin of fish. The average values of bioaccumulation of these heavy metals (BAF) were found in decreasing order of Cu > Cd > Fe > Cr > Pb. In this study, except Cd and Cr, all metals were found within the permissible limits. Both sediment and water from the selected site areas were also analyzed to observe their pollution levels in the order of; sediment > water > fish tissues.ConclusionThus, it was concluded that the Karachi environment was much more polluted than the Gwadar environment because it is in an industrial unit and a busy sea site for trade. Moreover, consuming muscles from this species is safe for human health except for iron toxicity, but the use of the liver is not beneficial for all selected metals. Thus, the present work will also be helpful to monitor these toxic metals in a food chain and maintain a healthy life, and reduce all kinds of health risks associated with them.     

硅藻重金属污染生态学研究进展

硅藻是水生生态系统健康的指示生物之一,对环境变化极为敏感,某些典型硅藻已应用于指示水体重金属污染.本文围绕地表水重金属污染,从毒性效应、生物吸附和累积、生态适应机制及生物指示与生态修复作用等方面,综述了硅藻重金属污染生态学研究进展,阐述重金属污染下硅藻的生长趋势和硅壳形态的变化,硅藻对重金属生物吸附和生物累积的差别,硅藻对重金属的表面络合和离子交换等生态适应机制,以及硅藻对水体重金属污染的指示作用和生态修复作用,为水生生态系统的重金属污染防治与预警技术提供科学依据.     

Lake size and fish diversity determine resource use and trophic position of a top predator in high‐latitude lakes

Prey preference of top predators and energy flow across habitat boundaries are of fundamental importance for structure and function of aquatic and terrestrial ecosystems, as they may have strong effects on production, species diversity, and food‐web stability. In lakes, littoral and pelagic food‐web compartments are typically coupled and controlled by generalist fish top predators. However, the extent and determinants of such coupling remains a topical area of ecological research and is largely unknown in oligotrophic high‐latitude lakes. We analyzed food‐web structure and resource use by a generalist top predator, the Arctic charr Salvelinus alpinus (L.), in 17 oligotrophic subarctic lakes covering a marked gradient in size (0.5–1084 km²) and fish species richness (2–13 species). We expected top predators to shift from littoral to pelagic energy sources with increasing lake size, as the availability of pelagic prey resources and the competition for littoral prey are both likely to be higher in large lakes with multispecies fish communities. We also expected top predators to occupy a higher trophic position in lakes with greater fish species richness due to potential substitution of intermediate consumers (prey fish) and increased piscivory by top predators. Based on stable carbon and nitrogen isotope analyses, the mean reliance of Arctic charr on littoral energy sources showed a significant negative relationship with lake surface area, whereas the mean trophic position of Arctic charr, reflecting the lake food‐chain length, increased with fish species richness. These results were supported by stomach contents data demonstrating a shift of Arctic charr from an invertebrate‐dominated diet to piscivory on pelagic fish. Our study highlights that, because they determine the main energy source (littoral vs. pelagic) and the trophic position of generalist top predators, ecosystem size and fish diversity are particularly important factors influencing function and structure of food webs in high‐latitude lakes.     

重金属在海洋食物链中的传递

近年来 ,金属在不同海洋食物链中摄食富集的定量研究得到越来越多的关注。自然环境中生物体内金属的浓度并不一定和生物在食物链中所处的营养级有相关关系 ,金属在生物体内的富集还受到生物的同化、排出等过程以及其它生理生化因子的影响。在经典的海洋浮游生物食物链中 (浮游植物→桡足类→鱼类 ) ,桡足类往往可以很有效地排出体内的金属 ,同时鱼类的金属同化率又很低 ,所以该食物链中金属的浓度随食物链水平增加而减少。目前研究发现只有甲基汞和铯 Cs会被食物链所放大。在以腹足动物为顶级捕食者的底栖食物链中 ,因为生物结合金属的效率很高 ,高同化率和低排出率导致金属浓度在生物体内得到放大。重金属在生物体内的可利用性可以通过测定同化率、排出率等参数、并结合考虑生物对该金属的消化行为 ,运用一个简易的动态模型来估算。已有的研究中人们多考虑金属的化学性质对食物链传递的影响。着重介绍了近年来国外对金属在不同海洋食物链 (底栖和浮游 )中的传递的研究成果 ,强调在金属的生物可利用性评估中 ,要充分考虑到动物的生理、生化过程的影响 ,同时也必须认识到不同的海洋生物有着复杂且不同的金属代谢机制     

Does the accumulation of trace metals in crustaceans affect their ecology—the amphipod example?

Crustaceans, like all aquatic invertebrates, take up and accumulate metals from a wide range of sources and the trace metal concentrations within their tissues and bodies show great variability. Trace metal uptake in crustaceans occurs from the water and food, either of which may be affected by the physico-chemical properties of the sediment. Accumulated metal concentrations in amphipods are contrasted with those of other crustaceans and examples are given to show how external and internal factors affect bioaccumulation. One of the major pathways for the uptake of trace metals is from solution directly through permeable surfaces including the gills. Changes in salinity and oxygen tension can modify the uptake characteristics from solution particularly in the case of interstitial water within sediments. Infaunal amphipods have direct contact with the sediment and the bioavailabilities of trace metals depend on the strength of the metal binding which is determined by a combination of properties including grain size, organic content, the presence of metals such as lead and iron as well as other ambient environmental conditions. Metal concentrations within amphipod bodies reflect the bioavailabilities of trace metals in their habitat. Body size is one of the major factors contributing to individual variability in trace metal concentrations within species. For some amphipod species, there are differences in trace metal accumulation with gender, breeding and developmental stage. In amphipods, accumulated body metal concentrations are the best biomarkers for environmental metal availabilities. Metal accumulation affects the ecology of crustaceans as a consequence of the energy costs associated with excreting and/or detoxifying the incoming metals. If the costs are significant, then this may result in reduced growth and reproduction. The effects of accumulated metals on communities have yet to be determined. Accumulated metals in crustacean prey species may be transferred along the food chain, but biomagnification in fish appears unlikely. One of the main ecological challenges is the need to link molecular biomarkers with ecologically relevant life history characteristics including growth, survival, reproduction and recruitment.     

First feeding diet of young brown trout fry in a temperate area: disentangling constraints and food selection

Trophic interactions are important factors structuring animal communities. We assessed the trophic relations of four fish species that live in sympatry in the River Ladra (NW Spain), and cluster analysis differentiated two feeding strategies: (1) species with omnivorous feeding habits, feeding mainly on detritus and plant material but with aquatic macroinvertebrates as an important complement (Achondrostoma arcasii and Pseudochondrostoma duriense) and (2) species feeding mainly (Salmo trutta) or exclusively (Gasterosteus gymnurus) on aquatic macroinvertebrates. Concerning ingested macroinvertebrates, the trophic overlap was quantified using Schoener’s index and the results obtained revealed a high diet overlap among the species (from 81.3 up to 99.2%). In order to get a deeper insight into mechanisms of fish species coexistence, we used ten biological and ecological traits of macroinvertebrate prey to discriminate feeding preferences. As a result, despite the high similarity among the diets, our analyses suggest that differences in diel activity patterns and drift behaviour of preys, as well as differences in the prey size, are important adaptive features that may reduce the inter-specific competition in the fish community and permit the partitioning of food that allows coexistence.     

Development of dietary specializations in a summer community of juvenile fishes

Synopsis Patterns of food use and food availability were analysed in a species rich summer weedbed community of juvenile lake fish to elucidate ontogenetic and ecological adaptations facilitating species co-existence and rapid growth. It was found that: (a) the community was based on the period of high seasonal invertebrate abundance linked to the spring-summer proliferation of macrophytes: food was not limiting; (b) diet separations of individual fish species were high. In mid-July when nine species were present, Schoener diet overlap values exceeded 0.25 in only ten of 36 pairs of combinations. This contrasted with findings from a preceding May-June community of larval fish (Keast 1980); (c) mouth size helped channel the species towards different diets; and (d) diets of the early juveniles were distinct from those of the larvae, and late juveniles and adults of their species. At both the species and community level, ontogenetic and ecological developments have evolved in response to the opportunities created by an annually repetitive resource base.     

Potential hazards associated with the consumption of Scombridae fish: Infection and toxicity from raw material and processing

Scombridae fish (tuna, bonito and mackerel) have significant ecological and economic values. They are very appreciated by consumers worldwide for their high-quality flesh and for their high nutritional value. However, consumption of Scombridae fish is potentially hazardous. Indeed, several cases of infections and toxicity linked to the consumption of Scombridae fish as raw, or processed food products have been reported worldwide. In this review, we presented the most common health risks associated with Scombridae fish consumption. Diseases associated with the consumption of these fish are generally infectious or toxic and are caused by biological hazards, such as bacteria, viruses, parasites or chemicals hazards that enter the body through contaminated fish (polycyclic aromatic hydrocarbons, histamine) or by physical contaminants, such as heavy metals. The risks of contamination exist throughout the food chain, from primary production to the preparation of products for consumption.     

Spatially variable effects of copper on sessile invertebrates across a marina

Heavy metals often occur at elevated concentrations in bays and estuaries surrounded by urbanised areas and can cause substantial ecological changes to marine communities. The toxic effect of heavy metals can be modified by a several physico-chemical processes in the marine environment. These processes can vary greatly over small scales, so it is likely that the ecological effects of heavy metals on marine biota also vary substantially over similar spatial scales. We used a manipulative field experiment to assess the spatial variation in the effect of copper on sessile invertebrates within a marina and tested whether this variation was influenced by variation in localised water flow. Effects of copper were not consistent over relatively small spatial scales (i.e. metres) for all sessile invertebrate species. Three of the twenty sessile invertebrates from our experimental assemblages showed significant small scale variation in the effect of copper at the scale of metres. For these taxa, the effect of copper varied in magnitude and direction. We had predicted that the effect of copper would diminish with increased water flow, but this did not occur for any taxa. We suggest that variations in the presence of organic or inorganic compounds or in pH within the marina may provide alternative explanations for the spatially variable effects detected in this study. Our study's findings highlight the need for future field assessments of the complex physical, chemical and biological influences on the ecological effects of heavy metals, particularly at small spatial scales. Such studies are the key to improving our prediction about the effects of heavy metals on marine organisms and aid in better characterisation of the risk of heavy metals in the marine environment.     

广东惠州3类海洋经济物种体内重金属含量分析和健康风险评估

海洋渔业资源是自然资源的重要组成部分,海洋经济物种体内重金属含量直接影响到人们身体健康。利用2018年春季惠州市海洋渔业资源调查样品,分析了贝类、甲壳类、鱼类等3类27种海洋经济物种体内重金属Cu、Pb、Cd的含量特征,利用单因子污染指数(SFI)、金属污染指数(MPI)和目标危险系数(THQ)分别进行了重金属污染水平评价和健康风险评估,并探讨了海洋经济物种体内重金属的来源及影响因素。结果显示,(1)2018年春季,惠州海域3类海洋经济物种体内重金属元素含量由大到小皆为Cu>Pb>Cd。不同类海洋经济物种对同种重金属的富集能力有明显差异,方差分析显示,贝类体内Cu含量显著高于鱼类,Cd含量显著高于甲壳类和鱼类。(2)惠州海洋经济物种体内3种重金属元素含量的Pearson相关分析结果显示,Cu与Pb、Cd显著正相关,反映其具有同源性和类似生物地球化学行为,受到人为活动的影响。(3)SFI值反映,3类海洋经济物种体内Cu含量为正常背景值水平,Pb含量为轻度污染;贝类、鱼类体内Cd含量分别为轻度污染和中度污染,值得引起重视。MPI值由大到小为贝类>甲壳类>鱼类。整体说明,不同海洋经济物种体内重金属含量特征对生存环境质量有明显响应。(4)根据《无公害食品水产品中有毒有害物质限量》(NY 5073-2006),从1996年到2018年春季,惠州海域海洋经济物种体内Cu含量稳定,无超标样品;甲壳类、鱼类体内Pb、Cd含量超标需引起关注。(5)3类海洋经济物种的THQ值皆<1,由大到小顺序为贝类>甲壳类>鱼类,对人身健康无影响。     

Fish kairomones, its benefits and detriments: A model based study both from releaser and acceptor perspective

Kairomones have been documented as an infochemicals to convey information between individuals in aquatic system. However, whether the effect of fish kairomones on acceptor (zooplankton) is beneficial or detrimental is a debatable and unanswered issue. This may be due to lack of feasibility of experimentation. In this study, we theoretically explore how fish kairomones affect the aquatic food chain and provide possible explanation of such different behaviors of kairomones. To do this, we propose two hypotheses and formulate two simple mathematical models which resemble more realistic scenario synergetic with natural complex system. Our study suggests that vertical migration helps zooplankton species for proper conservation of its abundance by avoiding unnecessary over predation.     

The use of fish parasites as bioindicators of heavy metals in aquatic ecosystems: a review

Parasites are attracting increasing interest from parasite ecologists as potential indicators of environmental quality due to the variety of ways in which they respond to anthropogenic pollution. In environmental impact studies certain organisms provide valuable information about the chemical state of their environment not through their presence or absence but instead through their ability to concentrate environmental toxins within their tissues. Free living invertebrates, notably bivalve molluscs, are commonly employed in this role as `sentinel organisms' to monitor the concentrations of bioavailable metals in aquatic ecosystems. Also certain parasites, particularly intestinal acanthocephalans of fish, can accumulate heavy metals to concentrations orders of magnitude higher than those in the host tissues or the environment. The comparison of metal accumulation capacities between acanthocephalans and established free living sentinel organisms revealed significantly higher concentrations of several elements in Acanthocephalus lucii (Müller) than in the Zebra mussel Dreissena polymorpha (Pallas) which is a commonly used bioindicating organism in Europe. In contrast to the high heavy metal concentrations recorded in adult acanthocephalans, the larval stages in their respective crustacean intermediate hosts show little tendency to accumulate metals. A number of experimental studies demonstrate a clear time dependent accumulation of lead for acanthocephalans in their final hosts. These investigations provide evidence that the extremely high metal concentrations in intestinal acanthocephalans of fish are not the result of a slow process of accumulation but instead a relatively rapid uptake to a steady-state level. Thus, metal concentrations in adult acanthocephalans respond rapidly to changes in environmental exposure of their hosts. The value of parasites for environmental monitoring will be discussed in detail in the present article.     

拟水狼蛛对食物中镉的吸收和排泄及生物学响应

为明确拟水狼蛛对食物中镉的吸收和排泄及生物学响应,采用原子吸收光谱法检测了连续3代拟水狼蛛对食物中Cd²⁺的吸收和排泄情况,并测定了Cd²⁺对其生长发育、繁殖力和耐饥力的影响。结果表明:食物中过量的Cd²⁺能够通过食物链进行传递并在拟水狼蛛体内积累,积累量随拟水狼蛛代数的增加而增加,第2代和第3代拟水狼蛛体内Cd²⁺积累量浓度显著高于第1代中Cd²⁺积累量,第2代和第3代间差异不显著,积累量与消耗的黑腹果蝇数量极显著正相关,P<0.01;与消耗食物中Cd含量显著正相关,P<0.05。连续3代拟水狼蛛分别吸收了食物中65.4%、68.5%和69.1%的Cd,生物营养级放大因子分别为1.71、2.12和2.17。连续3代拟水狼蛛Cd排泄量极低。Cd处理能显著改变拟水狼蛛背胸甲宽、幼蛛存活率、生长历期和繁殖力。随拟水狼蛛受胁迫代数的增加,幼蛛存活率显著减少,生长历期显著延长。卵袋重量显著减轻,卵数目显著减少,卵体积显著升高。Cd处理还能显著降低拟水狼耐饥力。研究结果可为进一步研究环境中Cd沿土壤-昆虫-天敌传递、放大和生理耐受提供更为充分的理论依据。     

The nature of biodiversity in hypogean waters and how it is endangered

The specialised aquatic hypogean, i.e. stygobiotic, fauna has been recognised in some regions moderately rich. Slovenia, the broader Dinaric region, and Europe are particularly rich with about 7–8% of all Metazoa and about 40% of Crustacea species being stygobionts. The hypogean biotic diversity is in general predominantly a crustacean diversity. The high number of stygobiont Crustacea–Malacostraca species can be explained by the near absence of Insecta as well as by their high endemicity and sometimes additional specialisation, i.e. the spatial and ecological partition of the environment by the species. Although one cave system may exceptionally shelter up to 40 stygobiont species, they are distributed there into separate associations. Among more than 2000 described stygobiontic Malacostraca species, which include close to 950 Amphipoda, the species numbers within some genera are very high (e.g. Niphargus with 275 spp.). With 10 orders represented the higher taxonomic diversity of stygobiont Malacostraca matches that of fresh waters or the sea. Comparison of some faunas shows that the limiting factors for biodiversity might be the lower ecological diversity of habitats and restricted food resources underground, both brought about to a high degree by the darkness and absence of plants. Being K-strategists, stygobionts are endangered by any sudden changes in their environment. In the case of an increased food input by modest organic pollution, they can be outcompeted by energetically demanding but competitively stronger recent immigrants from surface.     

Effects of solar UV radiation on aquatic ecosystems and interactions with climate change.

Recent results continue to show the general consensus that ozone-related increases in UV-B radiation can negatively influence many aquatic species and aquatic ecosystems (e.g., lakes, rivers, marshes, oceans). Solar UV radiation penetrates to ecological significant depths in aquatic systems and can affect both marine and freshwater systems from major biomass producers (phytoplankton) to consumers (e.g., zooplankton, fish, etc.) higher in the food web. Many factors influence the depth of penetration of radiation into natural waters including dissolved organic compounds whose concentration and chemical composition are likely to be influenced by future climate and UV radiation variability. There is also considerable evidence that aquatic species utilize many mechanisms for photoprotection against excessive radiation. Often, these protective mechanisms pose conflicting selection pressures on species making UV radiation an additional stressor on the organism. It is at the ecosystem level where assessments of anthropogenic climate change and UV-related effects are interrelated and where much recent research has been directed. Several studies suggest that the influence of UV-B at the ecosystem level may be more pronounced on community and trophic level structure, and hence on subsequent biogeochemical cycles, than on biomass levels per se.     

Trophic niche differences between coexisting omnivores silver carp and bighead carp in a pelagic food web

Understanding how omnivorous consumers are affected by their resources and how this is expressed through the food chain is a fundamental issue in ecology. We used stable isotope analysis of archived scales of two pelagic single-chain omnivorous fish species, bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix), to reconstruct historical trophic interactions patterns along a gradient of resources. We found that, although bighead carp and silver carp utilize the similar resources from the pelagic food chain, they can coexist and persist not only by regulating their trophic position and trophic dissimilarity, but also by regulating trophic niche width. Omnivorous fish often exhibit flexible foraging strategies, which is closely related to the availability of ecologic context. We found a positive relationship between trophic dissimilarity and zooplankton density, which may indicate that the competitive interactions induce strong top-down effects on zooplankton, and/or that high zooplankton availability release the between-population trophic interaction through bottom-up effect. The trophic niche width of bighead carp was positively related with zooplankton availability, probably reflecting that the niche of an omnivore at a higher trophic position is more sensitive to high quality resources. Our results indicate how different aspects of the trophic partitioning of coexisting omnivores may be regulated by different ecological contexts. These alternatives are not mutually exclusive and further theoretical work should include both these mechanisms to re-evaluate the effects of omnivory on food web properties.     

Enzymatic indication of heavy metal toxicity to marine heterotrophic bacteria

The ecotoxicological effect of heavy metals on the dehydrogenase and catalase activities of marine heterotrophic bacteria was assessed in pure strains and in associations. The microorganisms from the surfaces of copper-containing materials had higher levels of enzyme activities and were inhibited by trace metals to a lesser degree. The data from the field and laboratory experiments suggest that catalase activity can provide an ecological indicator of the effects of heavy metals on the aquatic environment.     

大型真菌对重金属的生物富集作用及生态修复

大型真菌是一类重要的环境生物资源,对人类的生存具有重要作用.与绿色植物相比,大型真菌能够积累高浓度的Pb、Cd和Hg等重金属.本文论述了大型真菌对重金属的生物富集作用以及利用大型真菌进行重金属生态修复的优势,指出大型真菌种类、生态类型、富集重金属的生物学特性及其遗传潜能、大型真菌菌丝体和子实体的形态、部位、寿命以及结实间隔和环境因子等是影响大型真菌吸收和积累重金属的主要因素.筛选富集重金属功能强大、易于人工栽培、环境适应性强、便于后处理的大型真菌是今后研究的重要方向.     

重金属污染对鸟类的影响

鸟类属于高等脊椎动物，是食物链中的高级消费者，由于生物富集作用，鸟类容易受到环境中污染物质的影响。鸟类羽毛和卵壳中的重金属浓度可以反映其所处环境中重金属的污染状况，因此可以用鸟类作为指示生物来监测环境中的重金属污染。对重金属污染的来源和特征进行了介绍，阐述了重金属污染对环境安全构成威胁的原因，分析了汞、铅、镉、砷、铜等几种重金属元素在鸟体内富集的特点及其对鸟类的危害。重金属污染物在不同生物体内的浓度存在差异，反映出它们通过食物链的生物富集和放大，对环境和鸟类的毒害作用有所增加。建议选择野生鹭类、麻雀和喜鹊等鸟类作为指示生物监测环境中的重金属污染。