Karcher Denis B, Roth Florian, Carvalho Susana, El-Khaled Yusuf C, Tilstra Arjen, Kürten Benjamin, Struck Ulrich, Jones Burton H, Wild Christian
Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, Bremen, Germany.
Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia.
PeerJ. 2020 Apr 2;8:e8737. doi: 10.7717/peerj.8737. eCollection 2020.
While various sources increasingly release nutrients to the Red Sea, knowledge about their effects on benthic coral reef communities is scarce. Here, we provide the first comparative assessment of the response of all major benthic groups (hard and soft corals, turf algae and reef sands-together accounting for 80% of the benthic reef community) to in-situ eutrophication in a central Red Sea coral reef. For 8 weeks, dissolved inorganic nitrogen (DIN) concentrations were experimentally increased 3-fold above environmental background concentrations around natural benthic reef communities using a slow release fertilizer with 15% total nitrogen (N) content. We investigated which major functional groups took up the available N, and how this changed organic carbon (C) and N contents using elemental and stable isotope measurements. Findings revealed that hard corals (in their tissue), soft corals and turf algae incorporated fertilizer N as indicated by significant increases in δN by 8%, 27% and 28%, respectively. Among the investigated groups, C content significantly increased in sediments (+24%) and in turf algae (+33%). Altogether, this suggests that among the benthic organisms only turf algae were limited by N availability and thus benefited most from N addition. Thereby, based on higher C content, turf algae potentially gained competitive advantage over, for example, hard corals. Local management should, thus, particularly address DIN eutrophication by coastal development and consider the role of turf algae as potential bioindicator for eutrophication.
尽管各种来源不断向红海释放营养物质，但关于它们对底栖珊瑚礁群落影响的知识却很匮乏。在此，我们首次对红海中部珊瑚礁中所有主要底栖生物群体（硬珊瑚和软珊瑚、草皮藻以及礁砂，它们共同占底栖礁群落的80%）对原位富营养化的响应进行了比较评估。在8周时间里，使用总氮（N）含量为15%的缓释肥料，将天然底栖礁群落周围的溶解无机氮（DIN）浓度实验性地提高到环境背景浓度的3倍。我们研究了哪些主要功能群吸收了可用的氮，以及这如何通过元素和稳定同位素测量改变有机碳（C）和氮的含量。研究结果表明，硬珊瑚（在其组织中）、软珊瑚和草皮藻吸收了肥料中的氮，δN分别显著增加了8%、27%和28%。在所研究的群体中，沉积物中的碳含量显著增加（+24%），草皮藻中的碳含量也显著增加（+33%）。总体而言，这表明在底栖生物中，只有草皮藻受到氮可用性的限制，因此从添加氮中受益最大。由此，基于更高的碳含量，草皮藻可能比例如硬珊瑚获得竞争优势。因此，地方管理应特别应对沿海开发导致的DIN富营养化问题，并考虑草皮藻作为富营养化潜在生物指示物的作用。
