An investigation into what constitutes lethal wounding in Acanthaster planci and an assessment of the effects of regeneration on gonad production

Butler, Ian Robert Jacques (1994) An investigation into what constitutes lethal wounding in Acanthaster planci and an assessment of the effects of regeneration on gonad production. Masters (Research) thesis, James Cook University of North Queensland.

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The population outbreaks of the corallivorous asteroid Acanthaster planci have been of great interest to scientists, reef managers and the public for the last 25 years. As of yet, the causes of these outbreaks can only be surmised. A suite of hypotheses put forward to explain these outbreaks concerns the effect of predators on A. planci populations. One of these hypotheses suggests that predators, which have been reduced in number, previously controlled the starfish populations through mortal or sublethal predation.

This study focuses on what constitutes mortal damage to A. planci and, if damage is sublethal, whether subsequent healing and regeneration reduce gonad production.

Starfish in the population on Davies Reef, central Great Barrier Reef, were collected and subjected to a series of damage treatments (which included severed arms and bi- or trisection of the oral disc), then placed in cages to examine short term survival. Four separate experiments took place during 1991-1992, including both winter and summer. Some starfish were starved prior to the damage treatments. Additional small scale experiments were conducted to assess whether sex or density of the starfish in cages affected survival after damage.

Logistic regression models were produced to describe the variation in survival through the various levels of treatment. The level of damage consistently producing 100% mortality could not be determined. Mortality was highly variable among experiments and occurred in all treatments including controls. Increased damage generally resulted in increased proportions of starfish mortality, though this effect was reduced to differences between damaged and undamaged starfish when experiments were combined. Starvation was found to affect survival inconsistently. No seasonal effects on survival were detected. There were no significant effects of either density or sex on survival of treated starfish in cages. Size related effects could not be assessed due to insufficient numbers of significantly different sized starfish.

To assess the possible influences of regeneration on gonad production, starfish were collected from Davies Reef and adjacent Lynchs Reef. These starfish were examined for regeneration or damage. Their gonads were dissected out and weighed.

Wet gonad weight versus somatic weight was examined by regression analysis. The results for males and females differed. Total gonad weights were significantly reduced in regenerating males, showing that regeneration affects gonad production in males. Regenerating females, by contrast, did not show a reduction in total gonad weight. When individual arms of the same sample of starfish were considered, regression models indicated a significant difference in gonad weight between regenerating arms and non-regenerating arms in males, but not in females. Relationships between the lengths of the regenerating arms and gonad weights within those arms were found in both sexes. The gonad weights of the arms adjacent to those regenerating were not detectably influenced by the regenerating arms in either sex. Short arms (arms not showing regeneration but obviously different in length) did not show reduced gonad weight when compared to normal length arms.

Gonad weights in lateral halves of arms were also compared. No effects of regeneration on gonad weight could be detected in the arms damaged nor in the normal arms adjacent to those damaged, for either sex. The gonad weights at this level were quite small and the variability was great.

The results of these studies provide important information about Acanthaster planci. It is clear that A. planci are susceptible to damage and that damage may result in either reduced gonad production or mortality. However, the variability in the results suggest that A. planci has a complex, perhaps plastic, life history which is influenced by many factors.

Item ID: 47301
Item Type: Thesis (Masters (Research))
Keywords: Acanthaster planci; Crown-of-thorns starfish (COTS); gonads; lethality; mortal damage; mortality; predation; regeneration; reproductive organs; starvation; sublethal damage; wounding; wounds
Date Deposited: 29 Mar 2018 01:31
FoR Codes: 06 BIOLOGICAL SCIENCES > 0608 Zoology > 060803 Animal Developmental and Reproductive Biology @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 50%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
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