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 users. The dominance of jelly-clad zooplankton will likely persist while lakewater Ca levels remain low.

北美东部与西欧地区的软水湖泊中，钙（Ca）浓度正持续降低。本研究依托长期现代观测与古环境野外数据，证实该现象正引发加拿大湖泊的剧烈生态转变：原本占优势的富钙溞属（Daphnia）浮游植食动物，正被具胶鞘的贫钙竞争者冰川透明溞（Holopedium glacialis）取代。在部分湖泊中，大型无脊椎动物捕食压力的增强推动了这一转变——本地幽蚊属（Chaoborus spp.）与引进种长柱尾突溞（Bythotrephes longimanus）均为浮游动物食性类群，而具胶鞘的透明溞对这类捕食者相对不易被捕食。相较于溞属类群，透明溞的磷含量更低，因此枝角类浮游动物群落中透明溞占比的提升，会削弱食物网的营养传递效率；同时其种群绝对丰度的升高，也将长期给水务使用者带来隐患。只要湖水钙浓度持续处于低位，具胶鞘浮游动物的优势地位便将得以维持。