Habitat degradation drives increased gnathiid isopod ectoparasite infection rate on juvenile but not adult fish: dataset

Widespread coral mortality is leading to coral reef degradation worldwide. Many juvenile reef fishes settle on live coral and their predator-avoidance behaviour is disrupted in seawater exposed to dead corals, ultimately increasing predation risk. Gnathiid isopods are micropredatory fish ectoparasites that occur in higher abundances in dead coral. However, the effect of seawater associated with dead coral on the susceptibility of fish to micropredators has never been investigated. We tested whether the infection rate of cultured gnathiid ectoparasites on individual damselfish, Pomacentrus amboinensis Bleeker 1868, from two different ontogenetic stages (juveniles and adults) was influenced by seawater exposed to three different treatments: dead coral, live coral, or no coral. Seawater treatments were presumed to contain different chemical properties, and are meant to represent environmental changes associated with habitat degradation on coral reefs. Gnathiid infection of juvenile fish in seawater exposed to dead coral was twice as high as that of fish in live coral or no coral. Infection rates did not significantly differ between live coral and no coral treatments. In contrast to juveniles, the susceptibility of adults to gnathiids was not affected by seawater treatment. During experiments, juvenile fish mortality was relatively low, but was higher for infected fish (9.7 %), compared to fish held without exposure to gnathiids (1.7%). No mortality occurred in adult fish that became infected with gnathiids. Our results suggest that chemical cues released from dead corals and/or dead coral colonisers affect the ability of juvenile, but not adult fish to avoid parasite infection. Considering increased habitat degradation on coral reefs and that gnathiids are more abundant in dead coral substrate, it is possible that wild juvenile fish may experience increased susceptibility to parasitic infection and reduced survival rate. This highlights the importance of including parasitism in ecological studies of global environmental change.

Software/equipment used to create/collect the data: Excel

Software/equipment used to manipulate/analyse the data: R studio

全球范围内广泛发生的珊瑚死亡事件正引发珊瑚礁大面积退化。许多幼年期礁栖鱼类会选择在活珊瑚上栖息，而当海水接触过死亡珊瑚后，这类鱼类的避敌行为会受到干扰，最终使其被捕食的风险升高。颚虱等足类（Gnathiid isopods）是一类微型捕食性鱼类体外寄生虫，在死亡珊瑚生境中的种群丰度更高。然而，此前尚无研究探讨死亡珊瑚关联海水对鱼类感染微型捕食者的易感性的影响。

本研究针对两种不同发育阶段（幼体与成体）的安汶雀鲷（Pomacentrus amboinensis Bleeker 1868）个体，检验暴露于三种不同处理组的海水（死亡珊瑚组、活珊瑚组、无珊瑚组）是否会影响其被人工养殖颚虱体外寄生虫的感染率。预设各海水处理组具有不同的化学特征，该实验设计旨在模拟珊瑚礁生境退化相关的环境变化。

实验结果显示：死亡珊瑚组海水中的幼鱼颚虱感染率为活珊瑚组与无珊瑚组的两倍；活珊瑚组与无珊瑚组的感染率无显著差异。与幼体形成鲜明对比的是，成体对颚虱的易感性未受海水处理的影响。实验期间，幼鱼的整体死亡率较低，但感染颚虱的幼鱼死亡率（9.7%）高于未暴露于颚虱的幼鱼（1.7%）；受颚虱感染的成体未出现死亡情况。

本研究结果表明，死亡珊瑚及/或死亡珊瑚定植生物释放的化学信号，会干扰幼鱼而非成体的寄生虫感染规避能力。鉴于当前珊瑚礁生境退化加剧，且颚虱在死亡珊瑚基质中的丰度更高，野生幼鱼可能面临更高的寄生虫感染易感性与更低的存活率。这一发现凸显了将寄生现象纳入全球环境变化生态学研究的重要性。

数据创建/采集所用软件/设备：Excel
数据处理/分析所用软件/设备：R Studio