Click
here to close Hello! We notice that
you are using Internet Explorer, which is not supported by Echinobase
and may cause the site to display incorrectly. We suggest using a
current version of Chrome,
FireFox,
or Safari.
PLoS One
2016 Jan 01;1112:e0169048. doi: 10.1371/journal.pone.0169048.
Show Gene links
Show Anatomy links
Assessing Different Causes of Crown-of-Thorns Starfish Outbreaks and Appropriate Responses for Management on the Great Barrier Reef.
Babcock RC
,
Dambacher JM
,
Morello EB
,
Plagányi ÉE
,
Hayes KR
,
Sweatman HP
,
Pratchett MS
.
Abstract
The crown-of-thorns starfish Acanthaster planci (COTS) has contributed greatly to declines in coral cover on Australia''s Great Barrier Reef, and remains one of the major acute disturbances on Indo-Pacific coral reefs. Despite uncertainty about the underlying causes of outbreaks and the management responses that might address them, few studies have critically and directly compared competing hypotheses. This study uses qualitative modelling to compare hypotheses relating to outbreak initiation, explicitly considering the potential role of positive feedbacks, elevated nutrients, and removal of starfish predators by fishing. When nutrients and fishing are considered in isolation, the models indicate that a range of alternative hypotheses are capable of explaining outbreak initiation with similar levels of certainty. The models also suggest that outbreaks may be caused by multiple factors operating simultaneously, rather than by single proximal causes. As the complexity and realism of the models increased, the certainty of outcomes decreased, but key areas that require further research to improve the structure of the models were identified. Nutrient additions were likely to result in outbreaks only when COTS larvae alone benefitted from nutrients. Similarly, the effects of fishing on the decline of corals depended on the complexity of interactions among several categories of fishes. Our work suggests that management approaches which seek to be robust to model structure uncertainty should allow for multiple potential causes of outbreaks. Monitoring programs can provide tests of alternative potential causes of outbreaks if they specifically monitor all key taxa at reefs that are exposed to appropriate combinations of potential causal factors.
Fig 1. Qualitative model to assess the relative impacts of nutrients and predation on COTS populations.COTS outbreak overview, with human activities leading to increased nutrients (Nutrients) and fishing mortality (Fishing) of COTS predators (Pred). (a) No self-regulating feedback on COTS, with predator benefitting from COTS. (b) Positive self-regulating feedback on COTS, with predator benefiting from COTS (c) No self-regulating feedback on COTS with predators not deriving significant benefit from consumption of COTS (d) Positive self-regulating feedback on COTS with predators not deriving significant benefit from consumption of COTS. Rectangles denote external pressures, circles denote biological system components. New elements of the model structure introduced from one model to the next are denoted by *. Where elements have been removed they are depicted by a dashed line.
Fig 2. Nutrient input hypothesis for COTS closed and open population.COTS A: COTS adult, COTS J: COTS juvenile, COTS L: COTS larvae. (a) Closed COTS population where coral facilitates COTS juveniles. (b) Closed COTS population with no facilitation of COTS juveniles by corals (COTS juveniles increase with nutrient addition due to the effect of nutrients on COTS larvae therefore positive effects from nutrients flow directly to them) (c) Open COTS population where coral facilitates COTS juveniles (d) Open COTS population with no facilitation of COTS juveniles by corals.
Fig 3. Effects of nutrients on COTS (open population) and reef invertebrates.Invert: reef invertebrates, CCA: crustose coralline algae, COTS A: COTS adult, COTS J: COTS juvenile. (a) Coral facilitates invertebrate predators. (b) No facilitation by corals. (c) Coral facilitates invertebrate predators with no effect of nutrients on CCA (d) No facilitation of invertebrates by corals and no effect of nutrients on CCA.
Fig 4. Model of effects of nutrients on a broader range of larval groups.Effects of nutrients (Nutrients) on COTS (open population), reef invertebrates (Invert), and large (Fish L) and small (Fish S) predatory fishes; CCA: crustose coralline algae, COTS A: COTS adult, COTS J: COTS juvenile. (a) Nutrients facilitate larvae of invertebrates and fish groups as well as CCA. (b) Nutrients facilitate invertebrates and CCA only. (c) Nutrients facilitate fish but not invertebrates or CCA. (d) Nutrients facilitate CCA only.
Fig 5. Example of a more complex set of models of COTS -coral interactions.Effects of fishing (Fishing) and nutrients (Nutrients) on COTS open populations. Predicted responses to press perturbations were examined for each model for Nutrients or Fishing alone, and then Nutrients and Fishing in combination. (a) Nutrients benefit larvae of COTS as well as invertebrates, fish assemblages show high level of interaction through competition and predation. (b) Nutrients benefit larvae of COTS as well as invertebrates, fish assemblages show low levels of interaction (c) Nutrients benefit COTS larvae alone, fish assemblages show low levels of interaction (d) Nutrients benefit COTS larvae alone, fish assemblages show high levels of interaction. COTS A: COTS adult, COTS J: COTS juvenile, Fish L: targeted large fish predators, Fish N: non-target fish predators, Fish S: targeted small fish predators, Invert: invertebrates, Triton: Giant Triton. COTS A: COTS adult, COTS J: COTS juvenile, Fish L: targeted large fish predators, Fish N: non-target fish predators, Fish S: targeted small fish predators, Invert: invertebrates, Triton: Giant Triton.
Babcock,
Sperm Diffusion Models and In Situ Confirmation of Long-Distance Fertilization in the Free-Spawning Asteroid Acanthaster planci.
1994, Pubmed,
Echinobase
Babcock,
Sperm Diffusion Models and In Situ Confirmation of Long-Distance Fertilization in the Free-Spawning Asteroid Acanthaster planci.
1994,
Pubmed
,
Echinobase
Brodie,
Are increased nutrient inputs responsible for more outbreaks of crown-of-thorns starfish? An appraisal of the evidence.
2005,
Pubmed
,
Echinobase
Bruno,
Regional decline of coral cover in the Indo-Pacific: timing, extent, and subregional comparisons.
2007,
Pubmed
Colgan,
Coral Reef Recovery on Guam (Micronesia) After Catastrophic Predation by Acanthaster Planci.
1987,
Pubmed
,
Echinobase
Courchamp,
Inverse density dependence and the Allee effect.
1999,
Pubmed
Dambacher,
Life expectancy change in perturbed communities: derivation and qualitative analysis.
2005,
Pubmed
Dambacher,
Qualitative mathematical models to support ecosystem-based management of Australia's Northern Prawn Fishery.
2015,
Pubmed
Dambacher,
Understanding and predicting effects of modified interactions through a qualitative analysis of community structure.
2007,
Pubmed
Dambacher,
Qualitative stability and ambiguity in model ecosystems.
2003,
Pubmed
De'ath,
The 27-year decline of coral cover on the Great Barrier Reef and its causes.
2012,
Pubmed
,
Echinobase
Doherty,
An empirical test of recruitment limitation in a coral reef fish.
1994,
Pubmed
Hosack,
Assessing model structure uncertainty through an analysis of system feedback and Bayesian networks.
2008,
Pubmed
Kayal,
Predator crown-of-thorns starfish (Acanthaster planci) outbreak, mass mortality of corals, and cascading effects on reef fish and benthic communities.
2012,
Pubmed
,
Echinobase
Kroon,
Towards ecologically relevant targets for river pollutant loads to the Great Barrier Reef.
2012,
Pubmed
McCook,
Adaptive management of the Great Barrier Reef: a globally significant demonstration of the benefits of networks of marine reserves.
2010,
Pubmed
,
Echinobase
McCulloch,
Coral record of increased sediment flux to the inner Great Barrier Reef since European settlement.
2003,
Pubmed
Sweatman,
No-take reserves protect coral reefs from predatory starfish.
2008,
Pubmed
Vermeij,
The effects of nutrient enrichment and herbivore abundance on the ability of turf algae to overgrow coral in the Caribbean.
2010,
Pubmed
