1. Crustacean zooplankton perform diel vertical and horizontal migrations in lakes to avoid predators and/or exploit food resources more efficiently. Crustaceans may also move passively with convective flows that are generated by the nocturnal cooling of the surface water. Water in the shallow littoral zone cools faster than deeper pelagic waters. Therefore, bottom water moves from inshore to the pelagic zone while surface water moves in the opposite direction.
2. The purpose of this study was to determine if crustaceans performed horizontal movements in the bottom and surface layers of a mesotrophic lake, Lake Obsterno in north‐west Belarus. We installed plankton nets horizontally in the bottom and surface layers of the lake at three sites located at different distances from the shore. We hypothesised that (1) if crustaceans performed diel horizontal migration, they would move in identical directions in the bottom and surface layers either from nearshore to open waters in the evening and back in the morning, or vice versa; (2) if crustaceans moved with convective flows, they would be carried to the shore in the surface layer and to the open waters in the bottom layers.
3. Day and night air temperatures differed by more than 10°C over 24 hr. We assumed that the rates of convective currents were similar to those reported for other lakes exposed to a similar range of air temperatures. Rates of convective currents were also measured in Lake Obsterno and varied between 0.6–0.7 cm/s. These rates of convective currents were shown to exceed the cruise speed of planktonic crustaceans.
4. The direction of movement of the most abundant taxa coincided with the direction of convective currents in more than 90% of the cases in the bottom layer and 70–80% of the cases in the surface layer. The abundance of invertebrate predators (mainly predatory cladocerans and boatmen (Hemiptera, Heteroptera) was negatively related to the abundance of crustaceans in the surface layer. Deviations in the distribution patterns of some crustacean species compared to distributions induced by convection currents in the upper layers may have been associated with the avoidance of invertebrate predators and/or predator grazing.
5. Abundances of crustaceans were positively correlated between the sites located at different distances from the shore, and individual taxa were positively related to each other indicating that they moved in the same direction. Based on the fact that the directions of crustacean movements and convective currents mostly coincided, we concluded that convective currents passively carried the crustaceans.
6. At low light intensities and low predation pressure (by visual fish predators), the direction of horizontal movement by zooplankton was mainly determined by convective circulation generated by cooling of the lake surface. Actively swimming planktonic invertebrate predators are likely to move in the same direction as herbivorous crustaceans. Therefore, predators could influence zooplankton distribution regulated by convective flows. We suggest that studies of horizontal migration and coupling between pelagic and littoral zones need to account for diurnal water currents in lakes.

中文翻译：

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对流环流影响中营养湖泊沿岸带浮游甲壳类动物的水平运动

1. 甲壳类浮游动物在湖泊中进行diel垂直和水平迁移，以避免捕食者和/或更有效地开发食物资源。甲壳类动物也可能通过对地表水的夜间冷却而产生的对流而被动运动。浅海沿岸地区的水比深海中上层水冷却得更快。因此，底水从近海向深海带移动，而地表水则沿相反方向移动。
2. 这项研究的目的是确定甲壳类动物是否在白俄罗斯西北部的中营养湖奥伯斯特诺湖的底部和表层进行了水平运动。我们在距海岸不同距离的三个地点的湖底和表层水平安装了浮游生物网。我们假设（1）如果甲壳类动物进行了diel水平迁移，它们将在底层和表层中以相同的方向从近岸移动到傍晚的开阔水域，然后在早晨返回，反之亦然；（2）如果甲壳类动物以对流流动，它们将被带到表层的海岸和底层的开阔水域。
3. 在24小时内，白天和晚上的气温相差10°C以上。我们假设对流流率与其他暴露于相似温度范围内的湖泊的流率相似。还测量了奥伯斯特诺湖的对流流速，其变化范围为0.6-0.7 cm / s。这些对流速度显示出超过了浮游甲壳类动物的巡航速度。
4. 最丰富的分类单元的运动方向与对流的方向一致，在底层的案例中超过90％，在表层的案例中超过70-80％。无脊椎动物天敌的数量（主要是捕食的角动藻类和船夫（半翅目，异翅目））与表层甲壳类动物的数量呈负相关。与避免无脊椎动物掠食者和/或掠食者掠食有关。
5. 在距海岸不同距离的地点之间，甲壳类动物的丰度呈正相关，而各个分类单元彼此呈正相关，表明它们在同一方向上移动。基于甲壳动物运动和对流的方向基本重合的事实，我们得出结论，对流是被动携带甲壳动物的。
6. 在低光照强度和低捕食压力下（通过视觉鱼类捕食者），浮游动物水平运动的方向主要取决于湖面冷却所产生的对流循环。活跃地游动浮游无脊椎动物的食肉动物可能会以与草食甲壳类动物相同的方向运动。因此，天敌会影响对流对浮游动物分布的影响。我们建议对中上层带和滨海带之间水平迁移和耦合的研究需要考虑湖泊中的昼夜水流。