Patterns of movement and habitat use by adult crown-of-thorns starfishes (Acanthaster spp.)
will have a major bearing on their distribution, reproductive capacity, and impacts on coral
assemblages and reef ecosystems. The spatial and temporal scales over which crown-ofthorns starfish move will also have important implications for the scales at which they will be
most effectively managed. Movement patterns of crown-of-thorns starfish have been studied
previously, though mostly over small distances (metres) and limited timeframes (minutes to
hours). This study reports on explicit studies that measured the movement rates and
movement patterns of Pacific crown-of-thorns starfish (Acanthaster cf. solaris) at a range of
temporal and spatial scales. In the first instance, we measured the instantaneous movement
rates of starfish (n = 218) across different substrates; sand, coral rubble and consolidated
carbonate pavement. This study was conducted in a large (5m diameter) tank, using video
recordings that were then analysed to determine the mean and maximum rates of movement
over successive 15-second intervals.
To assess movement patterns of A. cf. solaris in the field, short-term tagging and movement
studies were undertaken at Rib Reef, in the central GBR. All starfish (n = 357) recorded on
semi-permanent transects were individually tagged using numbered pieces of flagging tape.
The precise position of each starfish (where detected) was then recorded during successive
surveys during day and night for up to 4 days. To further scale-up movement studies for crownof-thorns starfish we tagged 50 crown-of-thorns starfish using V7 (69KHZ) acoustic
transmitters, at Lodestone Reef or Big Broadhurst Reef. The position of these starfish relative
to acoustic receivers deployed 50-200m along the edge of the reef was recorded (at 3-minute
intervals) for up to 8 months. Passive acoustic monitoring was intended to provide greater
insights into longer-term (weeks to months) and larger-scale (kilometres) patterns of
movement for crown-of-thorns starfish, but provided much less resolution regarding fine-scale
movements of individual starfish.
Instantaneous measures of movement capacity for A. cf. solaris (in aquaria) showed that these
starfish are capable of moving at 20-35 cm per minute, and move fastest over sand. Despite
their capacity for movement, field-based studies suggested that crown-of-thorns starfish
actually move very little at scales of days to weeks, and even months. For starfish that were
tagged with temporary visual markers, the minimum displacement distance recorded for the
majority of starfish (88.0%) was <2m throughout the course of the study. Moreover, starfish
that did move to feed (mostly at night) often returned to the same resting location between
feeding bouts. Similarly, starfish tagged with acoustic transmitters for up to 6 months were only
ever detected on adjacent receivers with large overlap in their ranges, suggesting that all
starfish remained within 50-100m of where they were initially found and tagged for up to 6-
months. The frequency and duration of passive detections varied greatly among individual
starfish tagged with transmitters, with detections peaking in early hours of the morning.
While this study shows that it is possible to effectively tag crown-of-thorns starfish, both over
short and longer time-frames, there were considerable logistical challenges to documenting
occasional large-scale, and presumably quite rapid, displacement of individual starfish. It is
clear that crown-of-thorns starfish generally move very little and remain within localised areas
(even returning to the same sheltering location between successive feeding bouts) of moderate to high coral cover. However, Acanthaster spp. are also capable of moving large distances
when necessary, presumably when coral prey are locally depleted. It will be important to
understand the nature and scale of both modes of movement to effectively manage population
irruptions of crown-of-thorns starfish. Documenting the incidence and rates of movement
during these infrequent events remains a priority for future research
