Sigl, R; Laforsch, C: The Influence of Water Currents on Movement Patterns on Sand in the Crown-of-Thorns Seastar (Acanthaster cf. solaris), Diversity, 8(25) (2016), online: 25.11.2016, doi:10.3390/d8040025
Stichworte: movement; migration; outbreak; Acanthaster cf. solaris; water current; orientation; navigation; rheotaxis; crown-of-thorns seastar

Outbreaks of the coral-eating crown-of-thorns seastar (Acanthaster cf. solaris) threaten coral reefs of the Indo-Pacific. Movement patterns may play an important role in the spread of outbreak populations, but studies investigating adult movement behavior are scarce. It remains unknown if Acanthaster cf. solaris orientates in inter-reef areas using chemical, visual, or mechanical cues (e.g., water currents) or which trigger is used for the onset of movement. We investigated the movement patterns of adult starved, fed, and blinded A. cf. solaris on sand at two sites with different unidirectional water current strengths. We found that the movement direction of the seastars in strong currents was downstream, whereas movement in weaker currents was random and independent from the current direction. However, the directionality of movement was consistently high, independent of the nutritional state, its visual abilities, or current strength. Starved A. cf. solaris started to move significantly faster compared to fed individuals. Therefore, starvation might trigger the onset of movement. Our findings indicate that navigation of A. cf. solaris in inter-reef areas is inefficient. Movements between reefs may be random or current-dependent and finding a new reef from a distance subject to chance, unless it is only few meters away.

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