Environmental factors influencing benthic communities in the oxygen minimum zones on the Angolan and Namibian margins
Environmental factors influencing benthic communities in the oxygen minimum zones on the Angolan and Namibian margins
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DOI：
10.5194/bg-16-4337-2019
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发表时间：
2019-11-15
期刊：
影响因子：
4.9
通讯作者：
Mienis, Furu
中科院分区：
文献类型：
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作者：
Hanz, Ulrike;Wienberg, Claudia;Mienis, Furu
在非洲西南部边缘的最低氧气区观察到繁荣的底栖群落。在纳米比亚边缘，化石冷水珊瑚丘上长满了海绵和苔藓虫，而安哥拉边缘的特点是冷水珊瑚丘被活珊瑚礁覆盖。为了探索为什么这两个地区的底栖群落存在差异，我们利用电导率-温度-深度（CTD）样线和底部登陆器来评估当前的环境条件，以调查环境特性的空间和时间变化。近海底测量记录了纳米比亚边缘 0-0.15 mL L-1（(sic)0 %-9% 饱和度）和安哥拉边缘 0.5-1.5 mL L-1（(sic)7 %-18% 饱和度）的低溶解氧浓度，这与相对较高的温度（11.8-13.2 摄氏度和 6.4-12.6 摄氏度）有关。 分别）。人们发现半日正压潮汐与边缘地形相互作用，产生内波。这些潮汐运动将具有更适合特性的水从低氧区域的下方和上方输送到底栖群落。同时，观察到提供了大量和高质量的有机物，这是底栖动物的重要食物来源。在纳米比亚边缘，有机质直接源自地表生产区，而在安哥拉边缘，有机质的地球化学特征表明存在额外的粮食供应机制。在冷水珊瑚上方观察到的云层可能构成有机物质的储存库，通过潮汐混合促进食物颗粒的持续供应。我们的数据表明，纳米比亚边缘的底栖动物群以及安哥拉边缘的冷水珊瑚群落可以通过增加食物供应来弥补低氧和高温的不利条件，而纳米比亚边缘的缺氧条件目前是冷水珊瑚生长的限制因素。这项研究提供了一个例子，说明海底生态系统如何应对这种极端的环境条件，因为预计未来氧气最低区将因人类活动而扩大。
Thriving benthic communities were observed in the oxygen minimum zones along the southwestern African margin. On the Namibian margin, fossil cold-water coral mounds were overgrown by sponges and bryozoans, while the Angolan margin was characterized by cold-water coral mounds covered by a living coral reef. To explore why benthic communities differ in both areas, present-day environmental conditions were assessed, using conductivity-temperature-depth (CTD) transects and bottom landers to investigate spatial and temporal variations of environmental properties. Near-bottom measurements recorded low dissolved oxygen concentrations on the Namibian margin of 0-0.15 mL L-1 ((sic)0 %-9% saturation) and on the Angolan margin of 0.5-1.5 mL L-1 ((sic)7 %-18% saturation), which were associated with relatively high temperatures (11.8-13.2 degrees C and 6.4-12.6 degrees C, respectively). Semidiurnal barotropic tides were found to interact with the margin topography producing internal waves. These tidal movements deliver water with more suitable characteristics to the benthic communities from below and above the zone of low oxygen. Concurrently, the delivery of a high quantity and quality of organic matter was observed, being an important food source for the benthic fauna. On the Namibian margin, organic matter originated directly from the surface productive zone, whereas on the Angolan margin the geochemical signature of organic matter suggested an additional mechanism of food supply. A nepheloid layer observed above the cold-water corals may constitute a reservoir of organic matter, facilitating a constant supply of food particles by tidal mixing. Our data suggest that the benthic fauna on the Namibian margin, as well as the cold-water coral communities on the Angolan margin, may compensate for unfavorable conditions of low oxygen levels and high temperatures with enhanced availability of food, while anoxic conditions on the Namibian margin are at present a limiting factor for cold-water coral growth. This study provides an example of how benthic ecosystems cope with such extreme environmental conditions since it is expected that oxygen minimum zones will expand in the future due to anthropogenic activities.