Table_1_Macrofauna Associated With a Rhodolith Bed at an Oceanic Island in the Eastern Tropical Pacific (Isla del Coco National Park, Costa Rica).docx

Rhodoliths are round calcareous red algae that form extensive beds and associated with them are a diverse suite of species. Rhodolith beds are among the least known coastal–marine ecosystems, and even less is understood about their associated flora and fauna. Here, we present an evaluation of the biodiversity larger than 500 μm associated with rhodoliths at Isla del Coco National Park, Costa Rica, an oceanic island in the Eastern Tropical Pacific, 500 km offshore of the mainland. This research determined the influence of rhodolith degree of aggregation (distance among individual rhodolith) as well as rhodolith complexity, volume, and mass in relation to the diversity, composition, and biomass of the associated fauna. A total of 145 taxa were collected in 60 rhodolith samples. Arthropods, polychaetes, and mollusks were the dominant taxa in terms of richness, and crustaceans + acari represented >50% of the total abundance. Five potentially new species were collected in this study. Collections identified 31 new records, with 20 of them being newly reported genera for Isla del Coco. Many of the organisms found were juveniles as well as adult stages bearing eggs, demonstrating the importance of this ecosystem. The faunal composition changed along the gradient of rhodolith aggregation. Moderately aggregated rhodoliths (separated by 5 to 10 cm) had the highest diversity, with the highest averages of taxon richness and total numerical abundance and the highest faunal biomass. There were more organisms in more complex rhodoliths; nevertheless, the complexity of the rhodolith did not affect the number of taxa or total organism biomass. Larger rhodoliths, in size and mass, favored higher amounts of taxa and organisms. The rhodolith bed studied is an example of the intermediate disturbance hypothesis because the highest value of biodiversity of invertebrates was at the moderate aggregation level of rhodoliths. In this density of rhodoliths, the fauna was less exposed to hard environmental conditions and prevented dominant species.

红藻球（rhodoliths）是一类圆形钙质红藻，可形成大面积藻床，其伴生物种类群极为多样。红藻球床是目前认知程度最低的近岸海洋生态系统之一，对其伴生动植物区系的了解更是匮乏。本研究针对哥斯达黎加可可岛国家公园（Isla del Coco National Park）内的红藻球床开展生物多样性评估，该区域为东热带太平洋的离岸海岛，距大陆海岸线500公里，本次评估聚焦尺寸大于500μm的伴生生物。研究分析了红藻球聚集程度（即单个红藻球间的间距）、复杂度、体积与质量，及其对伴生动物群落多样性、组成结构与生物量的影响。本次研究共在60份红藻球样本中采集到145个分类单元。从分类单元丰富度来看，节肢动物、多毛类与软体动物为优势类群；甲壳类+螨类的个体总数占总丰度的50%以上。本研究共采集到5个疑似新物种，同时发现31个新分布记录，其中20个属为可可岛的首次报道。采集到的生物多包含幼体与携卵成体，印证了该生态系统的重要生态价值。动物群落组成随红藻球聚集梯度发生显著变化：中等聚集程度（个体间距5~10cm）的红藻球床拥有最高的群落多样性，其分类单元丰富度、总个体丰度与群落生物量均达到峰值。结构更复杂的红藻球可承载更多的个体数量，但红藻球复杂度并未对分类单元数或总生物量产生显著影响。体积与质量更大的红藻球则更有利于提升伴生分类单元数与个体总数。本次研究的红藻球床符合中度干扰假说（intermediate disturbance hypothesis）：无脊椎动物的最高生物多样性出现在红藻球中等聚集的生境中。在此红藻球聚集密度下，伴生动物群落既能免受极端环境条件的胁迫，又可抑制优势物种独占生境。