Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.
PLoS One. 2013 Oct 24;8(10):e78579. doi: 10.1371/journal.pone.0078579. eCollection 2013.
Submerged macrophytes enhance water transparency and aquatic biodiversity in shallow water ecosystems. Therefore, the return of submerged macrophytes is the target of many lake restoration projects. However, at present, north-western European aquatic ecosystems are increasingly invaded by omnivorous exotic crayfish. We hypothesize that invasive crayfish pose a novel constraint on the regeneration of submerged macrophytes in restored lakes and may jeopardize restoration efforts. We experimentally investigated whether the invasive crayfish (Procambarus clarkii Girard) affects submerged macrophyte development in a Dutch peat lake where these crayfish are expanding rapidly. Seemingly favourable abiotic conditions for macrophyte growth existed in two 0.5 ha lake enclosures, which provided shelter and reduced turbidity, and in one lake enclosure iron was added to reduce internal nutrient loading, but macrophytes did not emerge. We transplanted three submerged macrophyte species in a full factorial exclosure experiment, where we separated the effect of crayfish from large vertebrates using different mesh sizes combined with a caging treatment stocked with crayfish only. The three transplanted macrophytes grew rapidly when protected from grazing in both lake enclosures, demonstrating that abiotic conditions for growth were suitable. Crayfish strongly reduced biomass and survival of all three macrophyte species while waterfowl and fish had no additive effects. Gut contents showed that crayfish were mostly carnivorous, but also consumed macrophytes. We show that P. clarkii strongly inhibit macrophyte development once favourable abiotic conditions for macrophyte growth are restored. Therefore, expansion of invasive crayfish poses a novel threat to the restoration of shallow water bodies in north-western Europe. Prevention of introduction and spread of crayfish is urgent, as management of invasive crayfish populations is very difficult.
沉水植物增加了浅水生态系统的水透明度和水生生物多样性。因此，沉水植物的恢复是许多湖泊修复项目的目标。然而，目前，西北欧水生生态系统越来越受到杂食性外来小龙虾的入侵。我们假设，入侵的小龙虾对恢复湖泊中沉水植物的再生构成了新的限制因素，并可能危及恢复工作。我们通过实验研究了这些小龙虾在荷兰泥炭湖中快速扩张的情况下，是否会对沉水植物的生长产生影响。在两个 0.5 公顷的湖泊围场内，似乎存在有利于沉水植物生长的非生物条件，这些围场提供了庇护所并降低了浊度，并且在一个围场内添加了铁以减少内部养分负荷，但沉水植物并没有出现。我们在一个全因子围封实验中移植了三种沉水植物，其中我们使用不同的网孔尺寸将小龙虾与大型脊椎动物的影响分开，并结合仅放养小龙虾的笼养处理。当在两个围场内免受放牧时，三种移植的沉水植物都迅速生长，表明生长的非生物条件适宜。小龙虾强烈减少了所有三种沉水植物的生物量和存活率，而水禽和鱼类则没有附加作用。肠道内容物表明，小龙虾主要是肉食性的，但也食用沉水植物。我们表明，一旦恢复了沉水植物生长的有利非生物条件，P. clarkii 就会强烈抑制沉水植物的发育。因此，入侵小龙虾的扩张对西北欧浅水水体的恢复构成了新的威胁。迫切需要防止小龙虾的引入和传播，因为管理入侵小龙虾种群非常困难。
