Daily Variation in the Feeding Activity of Pacific Crown-of-Thorns Starfish (Acanthaster cf. solaris)

Abstract

The ecological impact of crown-of-thorns starfish (CoTS; Acanthaster spp.) on coral reefs is intrinsically linked to their feeding behaviour. Management thresholds designed to mitigate coral loss driven by elevated densities of crown-of-thorns starfish rely on accurate estimates of individual feeding rates. In this study, structure-from-motion photogrammetry and intensive tracking of adult Pacific CoTS over an extended survey period were used to generate three-dimensional, high-resolution estimates of daily feeding rates. Our findings revealed substantial variation in the areal extent of coral consumed, both across consecutive days and among individuals. Notably, CoTS did not feed consistently; feeding occurred on 65% of observation days, with 2-3 days periods of inactivity common. Despite this variability, mean daily feeding rates aligned with previous studies (1.35 coral colonies d^-1; 198.4 cm² day^-1 planar area, and 998.83 cm² day^-1 three-dimensional surface area). Across all tracked individuals (n = 8), feeding was recorded on 17 coral genera; however, Acropora alone accounted for 51% of colonies consumed and contributed 82% of the total three-dimensional surface area ingested during the survey period. This highlights the disproportionately large feeding yield derived from Acropora-dominated diets and raises important questions about how future declines in Acropora cover may impact CoTS feeding success and energetic intake.

Keywords: behaviour; coral reefs; disturbance; management.

Figure 1

Maps of study location and sites. (a) Lizard Island’s location in the northern Great Barrier Reef, Australia, depicted by the yellow box; (b) Lizard Island with survey locations Granite Bluff, Turtle Beach and Casuarina marked in green, highlighted by yellow boxes; (c) the locations of CoTS 1–3 tracked at Casuarina; and (d) the locations of CoTS 4–8 at Turtle Beach and Granite Bluff. Queensland Imagery online aerial photograph library. Accessed 18 May 2024. https://qimagery.information.qld.gov.au/.

Figure 2

Daily activity patterns of 8 individual starfish over the survey period (9–13 days). Green points represent the 3D surface areal extent (cm²) of coral consumed during each 24-h period, grey points represent 24-h periods when no coral was consumed. Days when no feeding observations were conducted (due to diving limitations) are marked as crossed circles. Dashed lines represent the average number of colonies consumed over the survey period. Pie charts represent the proportion of 24-h periods spent feeding (green).

Figure 3

Daily feeding rates of 8 individual starfish recorded over 9–13 consecutive days, presented as (a) number of colonies consumed per day, (b) planar projected area of coral consumed per day (cm²) and (c) total (3D) surface area of coral consumed per day (cm²). Each box plot represents feeding for a single starfish across multiple days of intensive sampling. Large black diamonds and thick horizontal lines represent mean and median values, respectively. Maximum body diameter of each individual CoTS is also presented in panel a.

Figure 4

Total (cumulative) feeding from 9 consecutive days of feeding by 8 individual starfish. Bars represent summed feeding and colours depict proportional feeding on different coral morphotaxa. Total feeding is presented as (a) total number of coral colonies consumed and (b) total 3D surface area of coral consumed (cm²).

Figure 5

Ageing process of feeding scars observed. (a) Visual progression of a feeding scar (genus Pocillopora) photographed over 14 days in this study. (b) Box plot showing the number of days (since consumption) at which the B2 colour threshold was surpassed for 9 tracked scars. The box plot line shows the median time, the box limits show the interquartile range, the whiskers show the 1.5× interquartile range and the filled diamond shows the mean. Each coloured point represents an individual scar for which the ageing period was quantified. The shapes and colours of each point indicate the coral taxon and sampling site of the scars.