COTS experiment


Crown-of-thorns starfish

 Acanthaster planci (crown of thorns sea star, COTS) outbreaks are a major source of disturbance for the GBR and other reefs in the Pacific area. Reasons for the outbreaks are still unknown, but the presently most widely accepted hypothesis is that increased land runoff in certain years fertilises plankton production and thus provide more food for COTS larvae. Higher amount of food leads to shortened larval life and a substantially higher survivorship of the larvae. These can then seed ‘primary outbreaks' in the Northern section of the GBR. Subsequent to primary outbreaks a further spread (south) of the COTS is promoted mainly through the vast number of larvae produced in primary outbreaks (because high density of spawners will produces disproportionally larger number of larvae, Allee effect). Thus, the key to understanding and preventing these outbreaks is to improve our understanding of larval ecology, including responses to stressors such as climate change and ocean acidification. Further studies on settlement dynamics will elucidate this process and potentially provide clues on how to manipulate (prevent) excessive settlement.

Crown-of-thorns starfish

Studies during the coming spawning season will be carried out in the SeaSim prototype focusing on testing new developed larval rearing systems to allow large scale larvae culture. Different culture techniques will be tested with the aim of raising larvae through to settlement. If successful, we are testing whether settlement of the larvae on crustose coralline algae is influenced by ocean acidification. Initial experimental work will commence to test the nutrient-limitation hypothesis. We will also determine the thermal window of COTS larvae and look at interactive effects of increased food and ocean acidification on COTS larvae. Future studies will include experiments under different plankton quantity and quality, in interaction with other environmental factors. To investigate the nutrient hypothesis in situ we plan to develop molecular markers which will allow us to quantify COTS larvae (not distinguishable microscopically from many other echinoderm larvae). This research also relies on laboratory larval cultures to verify and develop quantification methods.

Crown-of-thorns starfish larvae

Studies planned for this year are well under way with CCA being pre-incubated under different pCO2 conditions and aquarium systems for larval (and plankton as food items) rearing installed in SeaSim. These studies are in collaboration with SeaSim staff.  Given the need for clean water, especially low in nutrients and under controlled salinity, and the importance to vary environmental factors it is crucial for these experiments that SeaSim will commence operating under full potential as early as possible.