How important is the crustacean plankton for the maintenance of water clarity in shallow lakes with abundant submerged vegetation?
How important is the crustacean plankton for the maintenance of water clarity in shallow lakes with abundant submerged vegetation?
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DOI：
10.1046/j.1365-2427.2000.00552.x
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发表时间：
2000-06-01
影响因子：
2.7
通讯作者：
Andersson, G
中科院分区：
文献类型：
--
作者：
Blindow, I;Hargeby, A;Andersson, G
1.测定了5个浅水、中营养、富营养湖泊夏季滤食性微型甲壳类浮游动物的丰度和生物量，并计算了它们对浮游植物生物量的影响。其中三个湖泊的数据既有沉水植被密集和低浊度的年份(清水州)，也有植被稀疏和浑浊度高的年份(浑浊态)。在其他两个湖泊中，数据仅适用于清水条件。在所有湖泊中，夏季茂密的植被和清澈的水条件与甲壳类浮游生物的低丰度相吻合。在漂移的三个湖泊中，计算出的甲壳类浮游生物摄取的生物体积(滤水率)在清水条件下比混浊条件下低3-11倍。然而，由于在清水条件下浮游植物的生物量较低，来自微型甲壳动物的每日放牧压力(以浮游植物生物量的百分比表示)在各州之间没有差异。据估计，在五个湖泊中的三个湖泊中，食草动物每天占浮游植物生物量的比例不到10%，这表明浮游动物的过滤不是维持清水状况的最重要机制。在轮藻茂密林中的三个湖泊中发现了高密度的枝角类。然而，这些样本主要是与植物相关的分类群，即使在夜间也很少在植被之外发现。这表明与植物相关的浮游动物对维持植被外水体的清晰度没有重大影响。其中三个湖泊的枝角类春季丰度达到高峰。在其中的两个研究中，在清水和浑浊状态下都研究了季节性发育，在清水状态下春季高峰较低。捕食、食物供应不足或两者兼而有之可能解释了浮游动物密度低的原因。在以轮藻为主的湖泊中，浮游植物可能受到磷有效性低的限制。我们的结果表明，浮游动物放牧的重要性可能对保持湖泊的清水状态不太重要，这些湖泊拥有密集的、牢固的沉水植被。
1. We measured the abundance and biomass of filter-feeding microcrustacean zooplankton and calculated their grazing impact on phytoplankton biomass during summer in five shallow, mesotrophic to eutrophic lakes. For three of the lakes data exist both from years with dense submerged vegetation and low turbidity (the clearwater state), as well as from years characterised by sparse vegetation and high turbidity (the turbid state). In the other two lakes data are available only for clearwater conditions.2. In all lakes conditions of dense vegetation and clear water coincided with a low abundance of crustacean plankton during summer. In the three lakes that shifted, the calculated biovolume ingested by crustacean plankton (filtering rate) was 3-11 times lower during clearwater conditions compared with turbid conditions. Because phytoplankton biomass was lower during clearwater conditions, however, daily grazing pressure from microcrustacea (expressed as percentage of phytoplankton biomass) did not differ between states. In three of the five lakes, grazers were estimated to take less than 10% of the phytoplankton biomass per day, indicating filtration by zooplankton was not the most important mechanism to maintain clearwater conditions.3. High densities of Cladocera were found in three of the lakes within dense stands of Charophyta. However, these samples were dominated by plant-associated taxa that even during the night were rarely found outside the vegetation. This indicates that plant-associated zooplankton has no major influence on the maintenance of water clarity outside the vegetation.4. Spring peak abundance of Cladocera was observed in three of the lakes. In two of these, where seasonal development was studied in both the clearwater and the turbid state, spring peaks were lower during the clearwater state.5. Predation, low food availability or a combination of both may explain the low zooplankton densities. Phytoplankton may be limited by low phosphorus availability in the lakes dominated by Charophyta. Our results indicate that the importance of zooplankton grazing may have minor importance for the maintenance of the clearwater state in lakes with dense, well-established submerged vegetation.