Data from: The jellification of north temperate lakes

Calcium (Ca) concentrations are decreasing in softwater lakes across eastern North America and western Europe. Using long-term contemporary and palaeo-environmental field data, we show that this is precipitating a dramatic change in Canadian lakes: the replacement of previously dominant pelagic herbivores (Ca-rich Daphnia species) by Holopedium glacialis, a jelly-clad, Ca-poor competitor. In some lakes, this transformation is being facilitated by increases in macro-invertebrate predation, both from native (Chaoborus spp.) and introduced (Bythotrephes longimanus) zooplanktivores, to which Holopedium, with its jelly coat, is relatively invulnerable. Greater representation by Holopedium within cladoceran zooplankton communities will reduce nutrient transfer through food webs, given their lower phosphorus content relative to daphniids, and greater absolute abundances may pose long-term problems to water takers. The dominance of jelly-clad zooplankton will likely persist while lakewater Ca levels remain low.

北美东部与西欧的软水湖泊中，钙（Calcium, Ca）浓度正持续下降。本研究依托长期现代观测与古环境野外数据，证实该现象正推动加拿大湖泊发生剧烈生态转型：原本占主导地位的远洋植食性富钙溞属（Daphnia）物种，正被具胶被的贫钙竞争者透明薄皮溞（Holopedium glacialis）取代。在部分湖泊中，大型无脊椎动物捕食压力的提升进一步加速了这一转变——无论是本地幽蚊属（Chaoborus spp.）还是引入种长柱尾突溞（Bythotrephes longimanus）的浮游动物食性捕食，对带有胶被的透明薄皮溞均相对不易造成杀伤。相较于溞类，透明薄皮溞的磷含量更低，因此枝角类浮游动物群落中其占比提升将削弱食物网的营养传递效率；而其种群绝对丰度的升高，也可能长期对用水主体造成不利影响。只要湖泊水体钙浓度维持低位，具胶被的浮游动物的优势地位就将持续存在。