Visual orientation by the crown-of-thorns starfish (Acanthaster planci)

Abstract

Photoreception in echinoderms has been known for over 200 years, but their visual capabilities remain poorly understood. As has been reported for some asteroids, the crown-of-thorns starfish (Acanthaster planci) possess a seemingly advanced eye at the tip of each of its 7-23 arms. With such an array of eyes, the starfish can integrate a wide field of view of its surroundings. We hypothesise that, at close range, orientation and directional movements of the crown-of-thorns starfish are visually guided. In this study, the eyes and vision of A. planci were examined by means of light microscopy, electron microscopy, underwater goniometry, electroretinograms and behavioural experiments in the animals' natural habitat. We found that only animals with intact vision could orient to a nearby coral reef, whereas blinded animals, with olfaction intact, walked in random directions. The eye had peak sensitivity in the blue part (470 nm) of the visual spectrum and a narrow, horizontal visual field of approximately 100°wide and 30°high. With approximately 250 ommatidia in each adult compound eye and average interommatidial angles of 8°, crown-of-thorns starfish have the highest spatial resolution of any starfish studied to date. In addition, they have the slowest vision of all animals examined thus far, with a flicker fusion frequency of only 0.6-0.7 Hz. This may be adaptive as fast vision is not required for the detection of stationary objects such as reefs. In short, the eyes seem optimised for detecting large, dark, stationary objects contrasted against an ocean blue background. Our results show that the visual sense of the crown-of-thorns starfish is much more elaborate than has been thus far appreciated and is essential for orientation and localisation of suitable habitats.

The crowns have eyes: Multiple opsins found in the eyes of the Crown-of-Thorns StarfishAcanthaster planciincluding the first r-opsin utilized by a deuterostome eye

“…Whereas rhabdomeric opsins have been described in many protostome species as the primary opsin for vision (reviewed in [67] ), no deuterostome eye has previously been found to express an r-opsin. As A. planci eyes have been previously demonstrated to perform proper spatial vision [19][20][21] , our findings thus provide first evidence for a deuterostome eye utilizing an r-opsin for spatial vision.…”

“…They are compound eyes and structurally they resemble the eyes of arch clams and fan worms [17,18] with lensless ommatidia typically 20-40 µm in diameter. Depending on species, adult specimens have 50-300 ommatidia in each eye and recent studies have shown that this supports spatial resolution in the range of 8-17 degrees used for navigation [19][20][21] . These studies have also indicated that the ommatidia have a single population of photoreceptors which utilize an opsin with peak sensitivity in the deep blue part of the spectrum around 470 nm.…”

The crown-of-thorns starfish genome as a guide for biocontrol of this coral reef pest

“…The infrared spectrum is beyond the detection range of starfish photoreception (425-580 nm) and therefore does not interfere with overlying photoperiod lighting 64,65 . The tanks were exposed to regional photoperiod changes (19.25° S, 146.8° E) with full sunlight spectrum plasma units (Luxim Model GRO-41-01, Luma America) with crepuscular twilight ramping.…”

Thirty Years of Research on Crown-of-Thorns Starfish (1986–2016): Scientific Advances and Emerging Opportunities

“…Suzuki et al [149] reported large numbers of adult CoTS moving across shallow sand flats in Ishigaki Island, southern Japan, which were in very poor condition and ultimately became stranded at low tide. For the most part, adult CoTS in good condition and with reasonable access to coral prey will have limited impetus to move, whereas individuals that are starving are probably unlikely to succeed in traversing large distances between reefs, despite demonstrated capacity for detection of reef structures and selective migration toward coral-rich areas via "vision" or chemoreception [150][151][152][153]. It is very likely that CoTS can and do move between close positioned reefs, especially where there is contiguous reef habitat connecting reefs, but the limited temporal and spatial scales of previous movement studies (as well as the predominant focus on movement within coral habitats) do not really inform the capacity of CoTS to travel large distances between reefs.…”