Tropical marine biodiversity studies have been biased towards more accessible coastal habitats and shallow coral reefs, while deeper inter-reef habitats are less studied due to different survey challenges. One such inter-reef habitat is the ‘bioherms’ dominated by the calcareous Halimeda macroalgae. In the northern section of Australia’s Great Barrier Reef, Halimeda algal bioherms occupy >6,000 km² of the inter-reef seabed, more than twice the area of adjacent shallow coral reefs. Here, we describe the biodiversity of the plant, vertebrate and invertebrate communities inhabiting Halimeda bioherms. By combining previous spatial mapping with legacy benthic biodiversity datasets, we find that Halimeda bioherms are a critically important complex habitat that hosts higher average species richness and diversity for both plants and invertebrates than the surrounding inter-reef (non-coral reef) seascape. Furthermore, at the community level, the structure of the bioherm-associated biotic assemblage is distinct from the non-bioherm community, with 40% of Halimeda bioherm-associated species not recorded at any non-bioherm sites. These findings improve estimates of the biodiversity of the Great Barrier Reef and elevate Halimeda bioherms as a critically important inter-reef habitat. Regular long-term monitoring is required to detect potential impacts to inter-reef biodiversity and ecosystem structure and function under future climate change scenarios.

热带海洋生物多样性研究偏向于更容易接近的沿海栖息地和浅层珊瑚礁，而由于不同的调查挑战，对更深的珊瑚礁间栖息地的研究较少。一种这样的珊瑚礁间栖息地是由钙质哈利米达大型藻类主导的“生物礁”。在澳大利亚大堡礁北部，哈利米达藻类生物礁占据了超过 6,000 平方公里的^礁间海床，是相邻浅层珊瑚礁面积的两倍多。在这里，我们描述了居住在Halimeda bioherms的植物、脊椎动物和无脊椎动物群落的生物多样性。通过将以前的空间映射与遗留的底栖生物多样性数据集相结合，我们发现Halimeda生物礁是一个极其重要的复杂栖息地，与周围的礁间（非珊瑚礁）海景相比，植物和无脊椎动物的平均物种丰富度和多样性更高。此外，在群落层面，与生物礁相关的生物组合的结构与非生物礁群落不同，40% 的哈利米达与生物礁相关的物种没有记录在任何非生物礁地点。这些发现提高了对大堡礁生物多样性的估计，并将哈利梅达生物礁提升为至关重要的珊瑚间栖息地。需要定期进行长期监测，以发现在未来气候变化情景下对珊瑚礁间生物多样性和生态系统结构和功能的潜在影响。