Rhodoliths are free-living and morphologically diverse marine calcareous algae commonly distributed over the continental shelf seafloor. They increase the seabed structural complexity and are of potential value as feeding and reproductive grounds for a myriad of marine fauna. The higher structural seabed complexity within rhodolith beds may also increase benthic diversity by creating microhabitats, but this relationship has been rarely explored within rhodolith beds worldwide. Here we compared benthic macrofaunal (>500 µm) structure on rhodolith beds (nodule epifauna) and within unconsolidated sediments (sediment infauna) under high and low-density beds to test whether rhodolith bed density and nodule morphology influenced macrofaunal assemblages. We observed that macrofaunal density on nodules (2538 ± 288.7 ind·m−2) was 15-fold higher when compared to sediments under those beds (166 ± 38.8 ind·m−2). Rhodolith bed density was positively related to macrofaunal density, composition, and functional diversity on the rhodoliths. Low-density beds (61 ± 27.1 nodules·m−2) with discoid-shape nodules were dominated by peracarid crustaceans whereas high-density beds (204 ± 18.7 nodules·m−2) with spheroidal nodules were dominated by Annelid polychaetes. The sediment macrofauna was also positively influenced by the density of rhodolith nodules, which increased sediment carbonate and organic quality (protein and lipids) under high-density beds. Macrofaunal functional diversity was generally higher on rhodoliths, with low similarity (low nestedness) and high taxa turnover between macrofaunal assemblages of rhodoliths and sediments. These findings indicate that rhodolith beds provide an unique habitat for benthic macrofaunal communities, with exclusive functional and taxonomic richness that are likely not typical in the unconsolidated sediment below these beds in SE Brazil. This study highlights the importance of protecting rhodolith beds from multiple sources of anthropogenic disturbance and exploration on continental shelves.

中文翻译：

---

巴西东南部与红石床相关的大型底栖动物的分类和功能多样性


红藻是自由生活且形态多样的海洋钙质藻类，通常分布在大陆架海底。它们增加了海底结构的复杂性，并且作为多种海洋动物的觅食和繁殖地具有潜在价值。红石层内较高的海底结构复杂性也可能通过创造微生境来增加底栖多样性，但这种关系在全世界红石层内很少被探索。在这里，我们比较了红石床（结核表层动物群）和高低密度床下松散沉积物（沉积物内动物群）内的大型底栖动物（> 500 µm）结构，以测试红石床密度和结核形态是否影响大型动物群落。我们观察到，结核上的大型动物密度 (2538 ± 288.7 ind·m−2) 是这些床下沉积物 (166 ± 38.8 ind·m−2) 的 15 倍。红石床密度与红石上的大型动物密度、组成和功能多样性呈正相关。低密度层（61 ± 27.1 结核·m−2）为盘状结核，以囊虫甲壳类为主，高密度层（204 ± 18.7 结核·m−2）为球形结核，以环节动物为主。沉积物大型动物群也受到红石结核密度的积极影响，红石结核密度增加了高密度床下的沉积物碳酸盐和有机质量（蛋白质和脂质）。红石榴石上的大型动物功能多样性通常较高，红石榴石的大型动物组合和沉积物之间的相似性较低（嵌套性低）且类群更替较高。 这些发现表明，红石床为底栖大型动物群落提供了独特的栖息地，具有独特的功能和分类丰富性，这在巴西东南部这些床下面的松散沉积物中可能并不常见。这项研究强调了保护红石床免受多种人为干扰和大陆架勘探的重要性。