Macroalgal-dominated reefs are a prominent component of tropical seascapes providing food and shelter for many species whilst subsidising secondary productivity in coastal ecosystems. Monitoring and managing macroalgae require an understanding of key processes that alter these assemblages, especially at the local scale. Here we consider how sediment depth/cover and abundance of the urchin Tripneustes gratilla influence variation in community composition and physical structure of macroalgal patches within the World Heritage listed Ningaloo Reef, Western Australia. Our study found high urchin densities in sites with lower sediment cover and depth and that sediments, urchin abundance, and seascape position explained 32% of the spatial variation in macroalgal community composition with a greater occurrence of Sargassopsis, Caulerpa, Sirophysalis and Hormophysa in the lagoon where sediment cover/depth was high. Canopy height and cover of canopy-forming macroalgae were also greater where sediments were high and urchin abundance low. Macroalgal genera with a strong and robust thallus were found in sediment depths up to 6 cm as opposed to those with softer, fragile thalli that were found in sediments < 2 cm. Our results demonstrate that high densities of urchins and mobile sediments can have profound effects on the composition and structure of tropical macroalgal assemblages. Changes to macroalgal community composition and physical structure will have flow-on effects for ecological processes such as productivity and habitat use which can alter the ecosystem goods and services macroalgal-dominated habitats provide.

以大型藻类为主的珊瑚礁是热带海景的重要组成部分，为许多物种提供食物和住所，同时补贴沿海生态系统的二次生产力。监测和管理大型藻类需要了解改变这些组合的关键过程，尤其是在局部范围内。在这里，我们考虑了海胆Tripneustes gratilla 的沉积物深度/覆盖度和丰度如何影响西澳大利亚宁格鲁礁世界遗产名录中大型藻类斑块群落组成和物理结构的变化。我们的研究发现，在沉积物覆盖率和深度较低的地点，海胆密度较高，沉积物、海胆丰度和海景位置解释了大型藻类群落组成空间变化的 32%Sargassopsis , Caulerpa , Sirophysalis和Hormophysa在沉积物覆盖/深度高的泻湖中。在沉积物高而海胆丰度低的地方，形成冠层的大型藻类的冠层高度和盖度也更高。在最深 6 厘米的沉积物中发现了具有强大而健壮的藻类的大型藻类，而在< 2 厘米的沉积物中发现的具有较软、易碎的藻类的藻属。我们的研究结果表明，海胆和移动沉积物的高密度会对热带大型藻类群落的组成和结构产生深远的影响。大型藻类群落组成和物理结构的变化将对生产力和栖息地利用等生态过程产生持续影响，这可能会改变以大型藻类为主的栖息地提供的生态系统产品和服务。