Data from: Bias associated with the detectability of the coral-eating pest crown-of-thorns seastar 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.

棘冠海星（crown-of-thorns seastar, COTS，学名*Acanthaster planci*）的种群爆发会在印度-太平洋海域引发大范围珊瑚死亡。与多数海洋无脊椎动物类似，棘冠海星为夜行性物种，其日间的隐蔽行为会降低其被探测的概率，在为底栖生物提供大量庇护场所的结构复杂珊瑚礁生境中，这一现象尤为显著。我们针对结构复杂程度与棘冠海星种群密度各不相同的珊瑚礁生境，开展了广泛的日间与夜间调查。本研究检验了两个核心问题：一是棘冠海星的密度估算值在日间与夜间观测之间是否存在差异；二是该差异是否与棘冠海星种群密度、珊瑚礁结构复杂程度及观测空间尺度相关。研究结果显示，棘冠海星的密度估算值夜间平均较日间高出27%。棘冠海星的探测率差异随海星种群密度变化而改变，但与珊瑚礁结构复杂程度或观测尺度无显著关联。在较宽的海星密度区间内，日间调查对棘冠海星种群密度的低估现象均较为显著，因此该偏差可能会影响绝大多数爆发事件的评估结果。本研究表明，仅在日间开展的常规调查与防控行动中，可能有部分棘冠海星种群未被探测到，这一情况会对珊瑚礁的发展轨迹造成显著负面影响。若在珊瑚礁管理工作中纳入棘冠海星探测偏差的校正因素，可从整体上强化珊瑚礁管理效能。