Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Tasmania 7004, Australia.
ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland 4811, Australia.
Proc Biol Sci. 2020 Nov 11;287(1938):20201341. doi: 10.1098/rspb.2020.1341. Epub 2020 Nov 4.
Corallivorous crown-of-thorns starfishes ( spp.) can decimate coral assemblages on Indo-Pacific coral reefs during population outbreaks. While initial drivers of population irruptions leading to outbreaks remain largely unknown, subsequent dispersal of outbreaks appears coincident with depletion of coral prey. Here, we used time-lapse photography to characterize movement of the Pacific crown-of-thorns starfish ( cf. ) in the northern and southern Great Barrier Reef in 2015, during the fourth recorded population outbreak of the starfish, but prior to widespread coral bleaching. Daily tracking of 58 individuals over a total of 1117 h revealed all starfish to move a minimum of 0.52 m, with around half of all tracked starfish showing negligible daily displacement (less than 1 m day), ranging up to a maximum of 19 m day. Movement was primarily nocturnal and daily displacement varied spatially with variation in local availability of spp., which is the preferred coral prey. Two distinct behavioural modes emerged: (i) homing movement, whereby tracked paths (as tested against a random-walk-model) involved short displacement distances following distinct 'outward' movement to prey (typically displaying 'feeding scars') and 'homebound' movement to nearby shelter; versus (ii) roaming movement, whereby individuals showed directional movement beyond initial tracking positions without return. Logistic modelling revealed more than half of all tracked starfish demonstrated homing when local abundance (percentage cover) of preferred coral prey was greater than 33%. Our results reveal facultative homing by with the prey-dependent behavioural switch to roaming forays providing a mechanism explaining localized aggregations and diffusion of these population irruptions as prey is locally depleted.
珊瑚食性的棘冠海星（ spp.）在种群爆发期间可以大量捕食印度-太平洋珊瑚礁的珊瑚群落。虽然导致种群爆发的最初驱动因素在很大程度上尚不清楚，但随后的爆发扩散似乎与珊瑚猎物的消耗同时发生。在这里，我们使用延时摄影技术，在 2015 年记录的第四次棘冠海星种群爆发之前，在北和南大堡礁描述了太平洋棘冠海星（ cf.）的运动情况，但在此之前珊瑚已经广泛白化。对 58 只个体进行了为期 1117 小时的日跟踪，发现所有的海星都至少移动了 0.52 米，大约一半的被跟踪的海星表现出微不足道的日位移（每天不到 1 米），最大可达 19 米/天。运动主要在夜间进行，每日位移在局部 spp.（首选珊瑚猎物）的可用性存在差异的情况下存在空间差异。出现了两种截然不同的行为模式：（i）归巢运动，在这种模式下，跟踪路径（根据随机游走模型进行测试）涉及在明显的“向外”运动到猎物（通常显示“进食疤痕”）和“归巢”运动到附近的遮蔽物后，短距离的位移；（ii）漫游运动，个体在没有返回的情况下向初始跟踪位置之外的方向移动。逻辑模型显示，当首选珊瑚猎物的局部丰度（覆盖率）大于 33%时，超过一半的被跟踪的海星表现出归巢行为。我们的研究结果揭示了棘冠海星具有适应性的归巢行为，并且依赖于猎物的行为转变为漫游突袭，为解释这些种群爆发的局部聚集和扩散提供了一种机制，因为猎物在局部被消耗。
