Setup

Two 7-day mesocosm experiments were conducted in October 2012 at the Instituto Nacional de Desenvolvimento das Pescas (INDP), Mindelo, Cape Verde. Surface water was collected at night before the start of the respective experiment with RV Islândia south of São Vicente (16°44.4'N, 25°09.4'W) and transported to shore using four 600L food safe intermediate bulk containers. Sixteen mesocosm bags were distributed in four flow-through water baths and shaded with blue, transparent lids to approximately 20% of surface irradiation. Mesocosm bags were filled from the containers by gravity, using a submerged hose to minimize bubbles. The accurate volume inside the individual bags was calculated after addition of 1.5 mmol silicate and measuring the resulting silicate concentration. The volume ranged from 105.5 to 145 L. The experimental manipulation comprised addition of different amounts of inorganic N and P. In the first experiment, the P supply was changed at constant N supply in thirteen of the sixteen units, while in the second experiment the N supply was changed at constant P supply in twelve of the sixteen units. In addition to this, “cornerpoints” were chosen that were repeated during both experiments. Four cornerpoints should have been repeated, but setting the nutrient levels in one mesocosm was not succesfull and therefore this mesocosm also was set at the center point conditions. Experimental treatments were evenly distributed between the four water baths. Initial sampling of the mesocosms on day 1 of each run was conducted between 9:45 and 11:30. After nutrient manipulation, sampling was conducted on a daily basis between 09:00 and 10:30 for days 2 to 8.2012年10月，在佛得角明德卢的国家渔业发展研究所（Instituto Nacional de Desenvolvimento das Pescas, INDP）开展了两项为期7天的中宇宙（mesocosm）实验。在各实验开始前的夜间，使用‘Islândia’号考察船（RV Islândia）在圣维森特岛南部（北纬16°44.4′，西经25°09.4′）采集表层水，并通过4个600升食品级中型散装容器运至岸边。16个中宇宙实验袋被分配到4个流水浴槽中，并用蓝色透明盖子遮光，使光照强度降至表层辐照度的约20%。实验袋通过重力从容器中注水，使用浸没式软管以减少气泡产生。向每个实验袋中加入1.5毫摩尔硅酸盐后，通过测量其最终浓度计算袋内精确体积，体积范围为105.5至145升。实验处理包括添加不同量的无机氮（N）和磷（P）。在第一项实验中，16个单元中的13个保持氮供应恒定，改变磷供应；而在第二项实验中，16个单元中的12个保持磷供应恒定，改变氮供应。此外，选择了在两项实验中重复的‘角点（cornerpoints）’处理。本应重复4个角点，但其中一个中宇宙的营养水平设置未成功，因此该中宇宙也被设定为中心点条件。实验处理在4个浴槽间均匀分布。每项实验第1天的初始采样于9:45至11:30进行；营养盐处理后，第2至8天的采样为每日一次，时间在09:00至10:30之间。