Data from: Bias associated with the detectability of the coral-eating pest crown-of-thorns seastar (COTS) and implications for reef management

Outbreaks of the predator crown-of-thorns seastar (COTS) Acanthaster planci cause widespread coral mortality across the Indo-Pacific. Like many marine invertebrates, COTS is a nocturnal species whose cryptic behaviour during the day can affect its detectability, particularly in structurally complex reef habitats that provide many refuges for benthic creatures. We performed extensive day and night surveys of COTS populations in coral reef habitats showing differing levels of structural complexity and COTS abundance. We tested whether estimations of COTS density varied between day and night observations, and if the differences were related to changes in COTS abundance, reef structural complexity, and the spatial scale of observation. Estimations of COTS density were on average 27% higher at night than during the day. Differences in COTS detection varied with changing seastar abundance but not reef structural complexity or scale of observation. Underestimation of COTS abundance in daytime was significant for a broad seastar density range, thus potentially affecting most outbreak events. Our study suggests that portions of COTS populations can be undetected during conventional surveys and control campaigns, which are exclusively conducted by day, and significantly affect the trajectory of coral reefs. Accounting for bias in COTS detection can strengthen coral reef management broadly.

掠食性棘冠海星（crown-of-thorns seastar，COTS，学名*Acanthaster planci*）的种群暴发，会在印度-太平洋海域造成大范围珊瑚死亡。与多数海洋无脊椎动物类似，COTS为夜行性物种，其日间的隐蔽行为会降低可检测性，在为底栖生物提供大量庇护所的结构复杂珊瑚礁生境中，该问题尤为显著。我们针对结构复杂度与COTS种群丰度各不相同的珊瑚礁生境，开展了大范围的昼夜调查。我们检验了两项核心问题：一是COTS密度的估算值在昼夜观测间是否存在差异；二是该差异是否与COTS种群丰度、珊瑚礁结构复杂度及观测空间尺度相关。研究结果显示，夜间的COTS密度估算值平均较日间高出27%。COTS检测率的差异随海星种群丰度的变化而改变，但与珊瑚礁结构复杂度或观测尺度无显著关联。在较宽的海星密度区间内，日间对COTS种群丰度的低估均具有统计学显著性，因此该偏差可能对绝大多数暴发事件产生影响。本研究表明，仅在日间开展的常规调查与防控行动，可能会遗漏部分COTS种群，进而显著影响珊瑚礁的发展轨迹。将COTS检测偏差纳入考量，可从整体上强化珊瑚礁管理工作。