MCR LTER: Coral Reef: Landscape-scale patterns of nutrient enrichment in a coral reef ecosystem: implications for coral to algae phase shifts, Adam et al., Ecol. Appl.

These data and analyses code were generated in support of the manuscript: Adam TC, Burkepile DE, Holbrook SJ, Carpenter RC, Claudet J, Loiseau C, Thiault L, Brooks, AJ, Washburn L, and RJ Schmitt, Ecological Applications We investigated the potential role of anthropogenic nutrient loading in driving recent coral-to-macroalgae phase shifts on reefs in the lagoons surrounding Moorea, French Polynesia. We used nitrogen (N) tissue content and stable isotopes (δ15N) in an abundant macroalga (Turbinaria ornata) together with empirical models of nutrient discharge to describe spatial and temporal patterns of nutrient enrichment in the lagoons. Turbinaria ornata were collected at 190 sites around Moorea in January, May, and August 2016. These sampling periods corresponded with distinct seasonal shifts in rainfall and wave forcing. Our results revealed that patterns of N enrichment were linked to rainfall, wave-driven circulation, and distance from anthropogenic nutrient sources, especially human sewage. In addition to describing high resolution patterns of N enrichment from 2016, we also analyzed core MCR time series on N tissue content in Turbinaria ornata from three habitats (fringing reef, back reef, and reef crest) at the six core MCR LTER sites between 2007 and 2013. These data showed that fringing reefs have been consistently enriched in N relative to back reefs, which are enriched relative to the reef crest. Further, these patterns mirror long-term patterns of nitrate and nitrite concentrations in the water column. We also analyzed core MCR time series on benthic communities and fishes and found that back reef sites that were consistently enriched in N between 2007 and 2013 experienced large increases in macroalgae while macroalgae remained much less abundant at back reef sites with lower N. These phase shifts to macroalgae occurred despite island-wide increases in the density and biomass of herbivorous fishes over the time period. Together, these results indicate that nutrient loading may be an important driver of coral-to-macroalgae phase shifts in the lagoons of Moorea even though the reefs harbor an abundant and diverse herbivore assemblage, emphasizing the important role that bottom-up factors can play in driving coral-to-macroalgae phase shifts.本数据集与分析代码均为配合以下学术论文生成：Adam TC、Burkepile DE、Holbrook SJ、Carpenter RC、Claudet J、Loiseau C、Thiault L、Brooks AJ、Washburn L 及 RJ Schmitt，刊载于《Ecological Applications》。 本研究探究了人为养分负载在驱动法属波利尼西亚茉莉雅岛周边环礁湖近期珊瑚向大型藻类（macroalgae）相态转变（phase shifts）中的潜在作用。我们通过选取优势大型藻类团扇藻（Turbinaria ornata）的组织氮（N）含量与稳定同位素(δ¹⁵N)，结合养分排放经验模型，对环礁湖内养分富集的时空格局进行刻画。 2016年1月、5月与8月，我们在茉莉雅岛周边190个采样点采集了团扇藻样本；上述采样时段分别对应降雨与波浪动力的显著季节变化。研究结果显示，氮富集格局与降雨、波浪驱动的环流过程及距人为养分源（尤其是人类生活污水）的距离密切相关。 除刻画2016年的高分辨率氮富集格局外，我们还分析了2007至2013年间，6个茉莉雅珊瑚礁长期生态研究（Moorea Coral Reef Long-Term Ecological Research, MCR LTER）核心站点内，3类栖息地（岸礁、礁后区与礁脊）中团扇藻组织氮含量的MCR核心时间序列数据。数据显示，岸礁区的氮富集水平始终高于礁后区，而礁后区的氮富集水平又高于礁脊。此外，该格局与水柱中硝酸盐与亚硝酸盐浓度的长期变化趋势一致。 我们同时分析了底栖生物群落与鱼类的MCR核心时间序列数据，结果发现：2007至2013年间氮富集水平持续偏高的礁后区，其大型藻类覆盖度大幅提升；而氮水平较低的礁后区，大型藻类丰度始终维持在较低水平。尽管研究时段内全岛植食性鱼类的密度与生物量均有所增长，但此类向大型藻类的相态转变仍如期发生。 综合上述结果可知，即便该礁域拥有丰富且多样的植食性动物类群，人为养分负载仍可能是茉莉雅岛环礁湖内珊瑚向大型藻类相态转变的重要驱动因素，这一结果强调了上行因子在驱动珊瑚-大型藻类相态转变中发挥的关键作用。