SummaryThere is an assumption that tropical sea urchins are macroalgal grazers with the ability to control macroalgal expansion on degraded coral reefs. We surveyed abundances of Echinothrix calamaris, an urchin species common in the western Indian Ocean on 21 reefs of the inner Seychelles and predicted their density using habitat predictors in a modelling approach. Urchin densities were greatest on patch reef habitat types and declined with increasing macroalgal cover. Next, we experimentally investigated the macroalgae-urchin relationship by penning two sea urchin densities on macroalgal fields. Over six weeks, the highest density treatment (4.44 urchins m−2) cleared 13% of macroalgal cover. This moderate impact leads us to conclude that controlling macroalgal expansion is not likely to be one of the main functions of E. calamaris in the inner Seychelles given the current densities we found in our surveys (mean: 0.02 urchins m−2, maximum: 0.16 urchins m−2).

中文翻译：

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研究对退化珊瑚礁的大型藻类控制至关重要的海胆密度

摘要假设热带海胆是大型藻类食草动物，具有控制退化珊瑚礁上大型藻类扩张的能力。我们调查了丰富的鱿鱼，一种常见于西印度洋内塞舌尔群岛 21 个珊瑚礁的海胆物种，并在建模方法中使用栖息地预测器预测了它们的密度。海胆密度在斑块礁栖息地类型中最大，并随着大型藻类覆盖的增加而下降。接下来，我们通过在大型藻类场上绘制两个海胆密度来实验研究大型藻类-海胆的关系。六周内，最高密度的处理（4.44 海胆米-2) 清除了 13% 的大型藻类覆盖。这种适度的影响使我们得出结论，控制大型藻类的扩张不太可能是海藻的主要功能之一。E. 鱿鱼鉴于我们在调查中发现的当前密度（平均：0.02 海胆 m-2, 最大值：0.16 海胆米-2）。