Clements Cody S, Hay Mark E
Proc Biol Sci. 2015 Sep 7;282(1814). doi: 10.1098/rspb.2015.0714.
Indirect biotic effects arising from multispecies interactions can alter the structure and function of ecological communities--often in surprising ways that can vary in direction and magnitude. On Pacific coral reefs, predation by the crown-of-thorns sea star, Acanthaster planci, is associated with broad-scale losses of coral cover and increases of macroalgal cover. Macroalgal blooms increase coral-macroalgal competition and can generate further coral decline. However, using a combination of manipulative field experiments and observations, we demonstrate that macroalgae, such as Sargassum polycystum, produce associational refuges for corals and dramatically reduce their consumption by Acanthaster. Thus, as Acanthaster densities increase, macroalgae can become coral mutualists, despite being competitors that significantly suppress coral growth. Field feeding experiments revealed that the protective effects of macroalgae were strong enough to cause Acanthaster to consume low-preference corals instead of high-preference corals surrounded by macroalgae. This highlights the context-dependent nature of coral-algal interactions when consumers are common. Macroalgal creation of associational refuges from Acanthaster predation may have important implications for the structure,function and resilience of reef communities subject to an increasing number of biotic disturbances.
多物种相互作用产生的间接生物效应能够改变生态群落的结构和功能——其方式往往出人意料，在方向和程度上各不相同。在太平洋珊瑚礁上，棘冠海星（Acanthaster planci）的捕食与珊瑚覆盖率的大规模下降以及大型藻类覆盖率的增加有关。大型藻华会加剧珊瑚与大型藻类之间的竞争，并可能导致珊瑚进一步减少。然而，通过结合操纵性野外实验和观察，我们证明，诸如多囊马尾藻（Sargassum polycystum）之类的大型藻类为珊瑚提供了联合庇护所，并显著减少了棘冠海星对它们的啃食。因此，随着棘冠海星密度的增加，大型藻类尽管是会显著抑制珊瑚生长的竞争者，但也能成为珊瑚的共生伙伴。野外喂食实验表明，大型藻类的保护作用很强，足以使棘冠海星去啃食低偏好度的珊瑚，而非啃食被大型藻类环绕的高偏好度珊瑚。这凸显了在捕食者常见时，珊瑚与藻类相互作用依赖于环境的特性。大型藻类为珊瑚提供免受棘冠海星捕食的联合庇护所，这可能对遭受越来越多生物干扰的珊瑚礁群落的结构、功能和恢复力具有重要意义。
