Nutrient pollution is altering coastal ecosystems worldwide. On coral reefs, excess nutrients can favor the production of algae at the expense of reef‐building corals, yet the role of nutrients in driving community changes such as shifts from coral to macroalgae is not well understood. Here we investigate the potential role of anthropogenic nutrient loading in driving recent coral‐to‐macroalgae phase shifts on reefs in the lagoons surrounding the Pacific island of Moorea, French Polynesia. We use 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. We then employ time series data to test whether recent increases in macroalgae are associated with nutrients. Our results revealed that patterns of N enrichment were linked to several factors, including rainfall, wave‐driven circulation, and distance from anthropogenic nutrient sources, especially human sewage. Reefs near large watersheds, where inputs of N from sewage and agriculture are high, have been consistently enriched in N for at least the last decade. In many of these areas, corals have decreased and macroalgae have increased, while reefs with lower levels of N input have maintained high cover of coral and low cover of macroalgae. Importantly, these patchy phase shifts to macroalgae have occurred despite substantial 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. These results emphasize the important role that bottom‐up factors can play in driving coral‐to‐macroalgae phase shifts and underscore the critical importance of watershed management for reducing inputs of nutrients and other land‐based pollutants to coral reef ecosystems.

中文翻译：

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珊瑚礁生态系统中养分富集的景观尺度格局：对珊瑚到藻类相移的影响。

营养污染正在改变全世界的沿海生态系统。在珊瑚礁上，过多的养分会以造礁珊瑚为代价来促进藻类的产生，但是养分在推动社区变化（例如从珊瑚向大型藻类转变）中的作用尚不为人所知。在这里，我们调查了法属波利尼西亚太平洋岛莫雷阿岛周围泻湖中人为养分负荷在驱动近期珊瑚礁到微藻类相变的潜在作用。我们使用氮（N）组织内容和稳定同位素（δ ¹⁵在丰富大藻N）（Turbinaria姬蛙），以及描述泻湖中养分富集的时空分布的养分排放经验模型。然后，我们使用时间序列数据来测试近期大型藻类的增加是否与营养物质有关。我们的研究结果表明，氮的富集模式与多种因素有关，包括降雨，波浪驱动的循环以及与人为营养源（尤其是人类污水）的距离。至少在过去十年中，大型分水岭附近的珊瑚礁一直大量富集氮，污水和农业对氮的投入很高。在许多这些地区，珊瑚数量减少，大型藻类数量增加，而氮含量较低的珊瑚礁则保持了较高的珊瑚覆盖率和较低的大型藻类覆盖率。重要的，尽管在这段时间内，全草食性鱼类的密度和生物量显着增加，但这些斑块状向巨藻的相移还是发生了。总之，这些结果表明，即使礁石中蕴藏着丰富多样的草食动物，养分含量也可能是莫雷阿岛泻湖中珊瑚向宏藻相变的重要驱动力。这些结果强调了自下而上的因素可以在驱动珊瑚到宏藻的相变中发挥重要作用，并强调了流域管理对于减少养分和其他陆地污染物对珊瑚礁生态系统的投入的至关重要。这些结果表明，即使珊瑚礁中有大量多样的食草动物，营养成分的加载仍可能是莫雷阿岛泻湖中珊瑚向宏藻相变的重要驱动力。这些结果强调了自下而上的因素可以在驱动珊瑚到宏藻的相变中发挥重要作用，并强调了流域管理对于减少养分和其他陆地污染物对珊瑚礁生态系统的投入的至关重要。这些结果表明，即使珊瑚礁中有大量多样的食草动物，营养成分的加载可能是莫雷阿岛泻湖中珊瑚向宏藻相变的重要驱动力。这些结果强调了自下而上的因素可以在驱动珊瑚到宏藻的相变中发挥重要作用，并强调了流域管理对于减少养分和其他陆地污染物对珊瑚礁生态系统的投入的至关重要。