Abstract
Coral reefs all over the Indo-Pacific suffer from substantial damage caused by the crown-of-thorns seastar Acanthaster planci, a voracious predator that moves on and between reefs to seek out its coral prey. Chemoreception is thought to guide A. planci. As vision was recently introduced as another sense involved in seastar navigation, we investigated the potential role of vision for navigation in A. planci. We estimated the spatial resolution and visual field of the compound eye using histological sections and morphometric measurements. Field experiments in a semi-controlled environment revealed that vision in A. planci aids in finding reef structures at a distance of at least 5 m, whereas chemoreception seems to be effective only at very short distances. Hence, vision outweighs chemoreception at intermediate distances. A. planci might use vision to navigate between reef structures and to locate coral prey, therefore improving foraging efficiency, especially when multidirectional currents and omnipresent chemical cues on the reef hamper chemoreception.
Highlights
The crown-of-thorns seastar, Acanthaster planci, is an abundant echinoderm (Asteroidea: Valvatida) in coral reef communities of the Indo-Pacific[1]
Based on the minimum and maximum acceptance angles of the single ommatidia, the determination of the visual field of A. planci revealed that the entire compound eye covers a minimum angle of 115 ± 15° and maximum of 132 ± 17° horizontally (Fig. 2a)
We present further evidence for the use of vision in behaviour of the predatory seastar species A. planci
Summary
The crown-of-thorns seastar, Acanthaster planci, is an abundant echinoderm (Asteroidea: Valvatida) in coral reef communities of the Indo-Pacific[1]. A. planci is thought to be guided primarily by chemical cues released by corals[10,11] To detect these prey odours, A. planci, like all seastars, is equipped with chemoreceptors that are concentrated on sensory tube feet at the distal end of each arm[12]. It has been suggested that seastars use basic mechano-sensitive nerve endings in the cuticle to determine the current direction[21,22] Turbulent environments such as coral reefs constrain both rheotaxis and chemotaxis[16]. Considering the spatially very restricted reliability of chemical cues[25] and water currents among reefs, A. planci probably uses other senses such as vision. Correspondence and requests for materials should be addressed to www.nature.com/scientificreports/
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