Data from: Ocean acidification alters fish–jellyfish symbiosis

Symbiotic relationships are common in nature, and are important for individual fitness and sustaining species populations. Global change is rapidly altering environmental conditions, but, with the exception of coral–microalgae interactions, we know little of how this will affect symbiotic relationships. We here test how the effects of ocean acidification, from rising anthropogenic CO2 emissions, may alter symbiotic interactions between juvenile fish and their jellyfish hosts. Fishes treated with elevated seawater CO2 concentrations, as forecast for the end of the century on a business-as-usual greenhouse gas emission scenario, were negatively affected in their behaviour. The total time that fish (yellowtail scad) spent close to their jellyfish host in a choice arena where they could see and smell their host was approximately three times shorter under future compared with ambient CO2 conditions. Likewise, the mean number of attempts to associate with jellyfish was almost three times lower in CO2-treated compared with control fish, while only 63% (high CO2) versus 86% (control) of all individuals tested initiated an association at all. By contrast, none of three fish species tested were attracted solely to jellyfish olfactory cues under present-day CO2 conditions, suggesting that the altered fish–jellyfish association is not driven by negative effects of ocean acidification on olfaction. Because shelter is not widely available in the open water column and larvae of many (and often commercially important) pelagic species associate with jellyfish for protection against predators, modification of the fish–jellyfish symbiosis might lead to higher mortality and alter species population dynamics, and potentially have flow-on effects for their fisheries.

共生关系在自然界中普遍存在，对个体适合度与物种种群的维持至关重要。全球变化正快速改变环境条件，但除珊瑚-微藻共生互作外，我们对全球变化将如何影响其他共生关系仍知之甚少。本文探究了人为二氧化碳排放加剧引发的海洋酸化，可能如何改变幼鱼与其水母宿主之间的共生互作。在模拟本世纪末照常排放温室气体情景下的升高海水二氧化碳浓度环境中饲养的鱼类，其行为受到负面影响。在可同时视觉观察与嗅觉感知宿主的选择实验舱内，未来高二氧化碳条件下，黄尾鲹贴近水母宿主的总时长仅约为当前环境二氧化碳条件下的三分之一。同样地，高二氧化碳处理组鱼类尝试与水母建立关联的平均次数较对照组低近三分之二；且仅63%的高二氧化碳组受试个体能够发起关联行为，而对照组这一比例为86%。与之形成对照的是，在当前环境二氧化碳条件下，三种受试鱼类均不会仅被水母的嗅觉线索所吸引，这表明鱼-水母共生关系的改变并非由海洋酸化对鱼类嗅觉的负面影响所驱动。由于开阔水体中庇护场所极为匮乏，且诸多（通常兼具商业价值的）远洋物种的幼体均会依附水母以躲避捕食者，因此鱼-水母共生关系的改变可能会导致鱼类死亡率升高、物种种群动态发生改变，并进而对相关渔业产生连锁效应。