Data from: Metabarcoding dietary analysis of coral dwelling predatory fish demonstrates the minor contribution of coral mutualists to their highly partitioned, generalist diet

Understanding the role of predators in food webs can be challenging in highly diverse predator/prey systems composed of small cryptic species. DNA based dietary analysis can supplement predator removal experiments and provide high resolution for prey identification. Here we use a metabarcoding approach to provide initial insights into the diet and functional role of coral-dwelling predatory fish feeding on small invertebrates. Fish were collected in Moorea (French Polynesia) where the BIOCODE project has generated DNA barcodes for numerous coral associated invertebrate species. Pyrosequencing data revealed a total of 292 Operational Taxonomic Units (OTU) in the gut contents of the arc-eye hawkfish (Paracirrhites arcatus), the flame hawkfish (Neocirrhites armatus) and the coral croucher (Caracanthus maculatus). One hundred forty-nine (51%) of them had species-level matches in reference libraries (>98% similarity) while 76 additional OTUs (26%) could be identified to higher taxonomic levels. Decapods that have a mutualistic relationship with Pocillopora and are typically dominant among coral branches, represent a minor contribution of the predators’ diets. Instead, predators mainly consumed transient species including pelagic taxa such as copepods, chaetognaths and siphonophores suggesting non random feeding behavior. We also identified prey species known to have direct negative interactions with stony corals, such as Hapalocarcinus sp, a gall crab considered a coral parasite, as well as species of vermetid snails known for their deleterious effects on coral growth. Pocillopora DNA accounted for 20.8% and 20.1% of total number of sequences in the guts of the flame hawkfish and coral croucher but it was not detected in the guts of the arc-eye hawkfish. Comparison of diets among the three fishes demonstrates remarkable partitioning with nearly 80% of prey items consumed by only one predator. Overall, the taxonomic resolution provided by the metabarcoding approach highlights a highly complex interaction web and demonstrates that levels of trophic partitioning among coral reef fishes have likely been underestimated. Therefore, we strongly encourage further empirical approaches to dietary studies prior to making assumptions of trophic equivalency in food web reconstruction.在由隐秘小型物种构成的高度多样的捕食者-猎物系统中，解析捕食者在食物网中的作用颇具挑战。基于DNA的膳食分析可作为捕食者移除实验的补充手段，并能为猎物鉴定提供高分辨率的分析结果。本研究采用元条形码（metabarcoding）技术，首次揭示了以小型无脊椎动物为食的栖居珊瑚捕食性鱼类的食性及其功能角色。研究样本采集自法属波利尼西亚的莫雷阿岛（Moorea），该区域的BIOCODE项目已为众多珊瑚伴生无脊椎动物物种构建了DNA条形码。焦磷酸测序（pyrosequencing）数据显示，在圆眼尖嘴鹰鲷（Paracirrhites arcatus）、火焰鹰鲷（Neocirrhites armatus）以及珊瑚蹲伏鲷（Caracanthus maculatus）的肠道内容物中，共检出292个操作分类单元（Operational Taxonomic Units，OTU）。其中149个OTU（占比51%）在参考数据库中匹配到物种级别的序列（相似度>98%），另有76个OTU（占比26%）可鉴定至更高的分类阶元。与杯形珊瑚属（Pocillopora）存在互利共生关系、且通常在珊瑚枝丛中占优势的十足目动物，在捕食者的食性中仅占极小比例。相反，捕食者主要取食的是暂居性物种，包括桡足类（copepods）、毛颚动物（chaetognaths）和管水母类（siphonophores）等浮游类群，这表明其取食行为并非随机。本研究还鉴定出已知与石珊瑚存在直接负相互作用的猎物物种，例如被视为珊瑚寄生虫的瘿蟹哈帕兰卡蟹属（Hapalocarcinus sp.），以及已知会对珊瑚生长产生有害影响的龙介螺类（vermetid snails）。在火焰鹰鲷和珊瑚蹲伏鲷的肠道序列总数中，杯形珊瑚属（Pocillopora）的DNA分别占比20.8%和20.1%，但在圆眼尖嘴鹰鲷的肠道中未检测到该类群的DNA。对三种鱼类食性的对比分析显示，其食性分化极为显著：近80%的猎物仅被单一捕食者取食。总体而言，元条形码（metabarcoding）技术提供的分类分辨率揭示了一个极为复杂的相互作用网络，并表明珊瑚礁鱼类间的营养分化程度可能被低估了。因此，在基于营养等价性假设开展食物网重构研究之前，本研究强烈建议开展更多相关的食性实证研究。