Ectoparasitism on deep-sea fishes in the western North Atlantic: In situ observations from ROV surveys International Journal for Parasitology: Parasites and Wildlife

A complete understanding of how parasites influence marine ecosystem functioning requires characterizing a broad range of parasite-host interactions while determining the effects of parasitism in a variety of habitats. In deep-sea fishes, the prevalence of parasitism remains poorly understood. Knowledge of ectoparasitism, in particular, is limited because collection methods often cause dislodgment of ectoparasites from their hosts. High-definition video collected during 43 remotely operated vehicle surveys (2013–2014) provided the opportunity to examine ectoparasitism on fishes across habitats (open slope, canyon, seamount, cold seep) and depths (494–4689 m) off the northeastern U.S., while providing high-resolution images and valuable observations of fish behavior. Only 9% (n = 125 individuals) of all observed fishes (25 species) were confirmed with ectoparasites, but higher percentages (∼33%) were observed for some of the most abundant fish species (e.g., Antimora rostrata). Ectoparasites included two copepod families (Lernaeopodidae, Sphyriidae) that infected four host species, two isopod families (Cymothoidae, Aegidae) that infected three host species, and one isopod family (Gnathiidae) that infected 19 host species. Hyperparasitism was also observed. As host diversity declined with depth, ectoparasite diversity declined; only gnathiids were observed at depths down to 3260 m. Thus, gnathiids appear to be the most successful group to infect a diversity of fishes across a broad depth range in the deep sea. For three dominant fishes (A. rostrata, Nezumia bairdii, Synaphobranchus spp.), the abundance and intensity of ectoparasitism peaked in different depths and habitats depending on the host species examined. Notably, gnathiid infections were most intense on A. rostrata, particularly in submarine canyons, suggesting that these habitats may increase ectoparasite infections. Although ectoparasitism is often overlooked in deep-sea benthic communities, our results demonstrate that it occurs widely across a variety of habitats, depths, and locations and is a significant component of deep-sea biodiversity.

要全面厘清寄生虫对海洋生态系统功能的影响机制，需系统表征各类寄生虫-宿主互作关系，并明确寄生作用在不同生境中的效应。针对深海鱼类而言，寄生现象的流行率仍鲜为人知。其中，外寄生现象（ectoparasitism）的相关认知尤为匮乏，这是因为传统采集方法常会导致外寄生物从宿主身上脱落。2013至2014年间开展的43次遥控无人潜水器（remotely operated vehicle, ROV）调查所获取的高清视频，为研究美国东北部海域不同生境（开阔斜坡、峡谷、海山、冷泉）及水深（494~4689米）范围内鱼类的外寄生现象提供了契机，同时也获得了高分辨率影像与鱼类行为的珍贵观测数据。本次观测涵盖25种鱼类共125个个体，其中仅9%（样本量n=125）被确认存在外寄生现象，但部分优势鱼类物种的外寄生率可达约33%，例如长鳍银眼鲷（Antimora rostrata）。本次观测到的外寄生物包括：侵染4种宿主的桡足类2个科——颚虱科（Lernaeopodidae）与烟管鳋科（Sphyriidae），侵染3种宿主的等足目2个科——浪飘水虱科（Cymothoidae）与漂水虱科（Aegidae），以及侵染19种宿主的等足目颚虱形水虱科（Gnathiidae）。研究中还观测到了超寄生现象（hyperparasitism）。随着水深增加，宿主多样性逐渐降低，外寄生物多样性亦随之下降；在3260米以深的水域中仅能观测到颚虱形水虱科。由此可见，颚虱形水虱科是深海环境中最成功的外寄生物类群，能够侵染广泛水深范围内的多种鱼类。针对3种优势鱼类（长鳍银眼鲷A. rostrata、贝氏单趾鼬鳚Nezumia bairdii、合鳃鳗属Synaphobranchus spp.）而言，外寄生的丰度与感染强度均因宿主物种不同，在不同水深与生境中达到峰值。值得注意的是，颚虱形水虱科的侵染在长鳍银眼鲷（A. rostrata）身上最为严重，尤其是在海底峡谷生境中，这表明此类生境可能会提升外寄生的感染概率。尽管外寄生现象在深海底栖生物群落中常被忽视，但本研究结果表明，外寄生现象广泛分布于各类生境、水深与海域，是深海生物多样性的重要组成部分。