Stoneworts (Charales) are green algae that represent an important food resource for many waterbird species in Europe and elsewhere. Browsing avian herbivores (e.g. swan, goose, duck and coot species) consume Charales plant vegetative parts, by head-dipping, up-ending or diving. A lower fibre content and longer growing season may make Charales as attractive to such herbivores as sympatric submerged higher plant species in some circumstances. Charales respond to environmental stress (e.g. drought) by producing abundant diaspores, in the form of oospores (sexual) and bulbils (asexual), both rich in starch, generating abundant food for waterbirds at critical stages in their annual migratory cycles. Waterbirds feed on these by diving (e.g. common pochard Aythya ferina and red-crested pochard Netta rufina) or by filtering from the water column (e.g. dabbling duck species), ensuring dispersal of sexually produced and vegetative diaspores locally (because of predator swamping) and remotely (through endo- and ectozoochorous dispersal by long-distance migratory waterbirds). Greater invertebrate density and diversity associated with Charales canopies enhances their attractiveness over other submerged macrophyte beds to diving predators [e.g. tufted duck Aythya fuligula, common pochard and Eurasian coot Fulica atra (hereafter coot)]. Fish fry preying on these invertebrates use such vegetation as predator cover, in turn providing prey for avian piscivores such as grebes and cormorants. Abundant Charales contribute to maintaining a transparent water column due to canopy density, nutrient effects, dampening of sedimentation/remobilisation of suspended matter and nutrients and allelopathic effects on other plants (especially phytoplankton). Shallow, relatively eutrophic waters can flip between clear-water high-biodiversity (where Charales thrive) and turbid species-poor depauperate stable states (lacking Charales). Shifts between turbid conditions and rich submerged Charales beds have profound elevating effects on aquatic diversity, to which waterbirds show rapid aggregative responses, making them ideal indicator species of ecological change; in the case of Charales specialists (such as red-crested and common pochard), indicators of the presence and abundance of these plants. Large-bodied colonial nesting birds (e.g. cormorants, gulls, heron and egrets) aggregating along lake shores contribute high N and P loadings to water bodies sensitive to such external and internal inputs and can cause local eutrophication and potential loss of Charales. Despite variation from complete seasonal removal of Charales biomass to undetectable grazing effects by herbivorous birds, evidence suggests little effect of avian grazing on biomass accumulation or the stability of community composition (under otherwise stable conditions), but we urge more research on this under-researched topic. We also lack investigations of the relative foraging profitability of different Charales organs to waterbirds and the degree of viability of gyrogonites (fertilised and calcified oospores), vegetative bulbils and plant fragments after passage through the guts of waterbirds. We especially need to understand better how much the carbonate armour of these organs affects their viability/dispersal via waterbirds and urge more research on these neglected plants and their relationships and interactions with other organisms in the aquatic biota.

中文翻译：

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海藻（Charales）和水鸟之间的相互作用

石藻（Charales）是绿藻，是欧洲和其他地方许多水鸟物种的重要食物资源。鸟类食草动物（例如天鹅、鹅、鸭和白骨顶鸟）通过低头、倒立或潜水来消耗Charales植物的营养部分。在某些情况下，较低的纤维含量和较长的生长季节可能使夏拉目对食草动物具有与同域沉水高等植物一样的吸引力。轮藻通过产生丰富的水硬铝石来应对环境压力（例如干旱），卵孢子（有性）和珠芽（无性）形式均富含淀粉，为水鸟在每年迁徙周期的关键阶段提供丰富的食物。水鸟通过潜水（例如普通潜鸭Aythya ferina和红冠潜鸭Netta rufina）或通过从水柱中过滤（例如涉水鸭种）以这些物质为食，确保有性繁殖和营养性水硬铝石在当地扩散（因为捕食者沼泽）和远程（通过长距离迁徙水鸟的体内和体外传播）。与Charales冠层相关的无脊椎动物密度和多样性更大，增强了它们相对于其他水下大型植物床对潜水捕食者的吸引力[例如簇绒鸭Aythya fuligula，普通潜鸭和欧亚白顶黑顶鹬Fulica atra（以下简称“傻瓜”）]。捕食这些无脊椎动物的鱼苗利用这些植被作为捕食者的覆盖物，进而为鸊鷉和鸬鹚等鸟类食鱼动物提供猎物。由于树冠密度、养分效应、悬浮物和养分的沉降/再动员的抑制以及对其他植物（特别是浮游植物）的化感作用，丰富的Charales有助于维持透明的水柱。相对富营养化的浅水水域可以在清澈的高生物多样性（夏拉目鱼繁衍生息）和浑浊的物种贫乏的贫困稳定状态（缺乏夏拉目鱼）之间翻转。浑浊条件和丰富的水下Charales床之间的变化对水生生物多样性产生深远的影响，水鸟对此表现出快速的集体反应，使它们成为生态变化的理想指示物种；对于Charales专家（例如红冠潜鸭和普通潜鸭），这些植物的存在和丰富程度的指标。沿着湖岸聚集的大型群体筑巢鸟类（例如鸬鹚、海鸥、苍鹭和白鹭）会给对此类外部和内部输入敏感的水体带来高氮和磷负荷，并可能导致局部富营养化和潜在的Charales损失。尽管从Charales生物量的完全季节性去除到食草鸟类无法检测到的放牧效应存在差异，但有证据表明鸟类放牧对生物量积累或群落组成的稳定性（在其他稳定条件下）影响不大，但我们敦促对这一尚待研究的领域进行更多研究话题。我们还缺乏对不同Charales器官对水鸟的相对觅食能力以及gyrogonites（受精和钙化卵孢子）、营养珠芽和植物碎片通过水鸟肠道后的生存能力的调查。我们特别需要更好地了解这些器官的碳酸盐装甲在多大程度上影响它们通过水鸟的生存/扩散，并敦促对这些被忽视的植物及其与水生生物群中其他生物的关系和相互作用进行更多研究。