Feeding biology of the crown-of-thorns starfish, Acanthaster planci (Linnaeus)

Keesing, John Kenneth (1990) Feeding biology of the crown-of-thorns starfish, Acanthaster planci (Linnaeus). PhD thesis, James Cook University.

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Abstract

Field and laboratory studies were undertaken to examine aspects of the feeding biology of Acanthaster planci (Linnaeus) in the central region of the Great Barrier Reef. Day and night surveys were carried out to examine feeding periodicity, and measurements of feeding and movement rates were made by monitoring tagged animals. Diet and feeding preferences were assessed in the field and laboratory studies were undertaken to assess the importance of nutritional quality of food in governing feeding preferences.

Small starfish feed nocturnally and remain cryptic during the day. Large starfish are primarily diurnal feeders and are rarely cryptic. Starfish are most mobile around dawn and dusk. It is proposed that the observed behaviour patterns have evolved as a predator avoidance strategy with large starfish achieving a refuge in size. These size dependent behavioural patterns, together with changes in population size structure, have important implications for assessing the numbers of starfish remaining undetected in A. planci survey and control programs.

Rates of movement in A. planci are dependent on food availability. These are about 1 m.day¯¹ in areas of high coral cover and about 4 m.day¯¹ in patches of low coral cover. Starfish in extensive areas of depleted coral cover move at rates of about 10 m.day¯¹.

Feeding rates in A. planci are dependent on starfish size and season, being greatest prior to the summer spawning season. Starfish at Davies Reef in summer averaged 1.5 feeds per day, killing about 300 cm² of coral cover or 15 g DW (dry weight) of soft coral tissues per day. Biomass utilization is about 4 g DW or 90 kJ per day. Feeding rates in winter are about half those of summer. Feeding rate measurements were applied to ecological and physiological considerations in A. planci. The magnitude of changes to coral communities in terms of area and biomass of coral killed during A. planci outbreaks is substantial. Outbreaking populations (ca. 100000 starfish per reef) will kill thousands of square metres of coral; equivalent to hundreds of kilograms dry weight of soft tissues per day. Feeding rate measurements were used to predict a threshold population level of about 1000 starfish per km² which would cause minimal damage to coral communities on the Great Barrier Reef. It is evident that large scale fluctuations in A. planci populations can occur without causing extensive coral mortality. Comparison of physiological requirements with feeding rates confirms that, despite increased feeding rates in large adults, growth is determinant and senility of large A. planci can be expected. As suggested in previous studies, this occurs because as the starfish grows its capacity to feed cannot meet the demands of metabolising tissue.

The diet of A. planci is almost exclusively scleractinian corals (90 - 95 %). Non-coral prey are taken in increasing abundance in areas of low coral availability. A. planci exhibits strong feeding preferences in both the field and the laboratory. The scleractinian families Acroporidae and Pocilloporidae are most favoured. Non-preferred prey are taken in increasing abundance in areas depleted of favoured species. The nutritional value of different species of coral prey was assessed and related to the observed feeding preferences. Several attributes may affect a coral species suitability as food; these are surface area complexity, biomass, nutritional value and abundance. Prey preference was more closely related to a general assessment of food suitability than to the absolute predictions of optimal diet theory. It is proposed that the ability to feed more efficiently on certain prey types is the most important factor giving rise to observed and published patterns of prey selection.

Item ID: 24112
Item Type: Thesis (PhD)
Keywords: Acanthaster; COTs; crown of thorns starfish; Davies Reef; diet; diurnal variation; feeding behaviour; food preferences; movement; size; Wheeler Reef
Date Deposited: 13 Dec 2012 23:50
FoR Codes: 06 BIOLOGICAL SCIENCES > 0608 Zoology > 060801 Animal Behaviour @ 50%
06 BIOLOGICAL SCIENCES > 0608 Zoology > 060807 Animal Structure and Function @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
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