Biocontrol for coral health and resilience

Control of coral competitors, predators, pests and other invasive species will be critical to maximising the positive impact interventions can have in helping the Reef, resist, adapt and recover from the impacts of climate change. While predators, such as crown-of-thorns starfish, and competitors, such as macroalgae (seaweed), are a natural part of the Reef ecosystem, it is believed their populations or volumes are being increased by human disturbances and pollution which lead to excess nutrients in the reef waters. These increased populations are adding to the environmental stress on corals.

Macroalgal removal

Although naturally-occurring, and offering positive contributions to reef ecology as a food, habitat and fish nursery, macroalgae – or seaweed – when excessive, can compete with, and threaten coral on nearshore reefs.

Its volume on reefs can increase through excess nutrients from human disturbances and pollution, such as agricultural run-off. Macroalgae can negatively affect coral by competing for space and other resources, overshading and transmitting disease. It can also reduce coral larvae production, and inhibit young coral settlement, growth and survival. Manual removal is labour-intensive.

The greatest potential for large-scale and long-term management is through nurturing biological removal agents such plant-eating urchins and fish.



Photo by J Maynard, Copyright, Commonwealth of Australia (GBRMPA)

Managing predators

The Great Barrier Reef Marine Park Authority manages outbreaks of native, coral-eating crown-of-thorns starfish in the marine park. These starfish represent a major threat to Great Barrier Reef coral cover. Such outbreaks are believed to be exacerbated by human activity such as nutrient run-off from farming. Modelling during the RRAP Concept Feasibility Study found intensified control of crown-of-thorns starfish will be critical to the efficacy of RRAP interventions. There is currently no method to fully prevent or arrest outbreaks, in part because juvenile starfish are difficult to detect or remove effectively using conventional means. A separate, continuing R&D effort is needed to prevent crown-of-thorns starfish outbreaks. This is not included in the RRAP R&D Program as there are already existing research and development programs dedicated to this method of intervention. View this short video on the latest CSIRO research into crown-of-thorns starfish control.

The Drupella sea snail is another coral predator. It may be possible to control the snail population using 'push-pull' technology which, for example could use pheromones to attract the snails to locations where they could be removed. This technology does not currently exist and would need to be researched and developed.

Photo: Crown-of-thorns starfish control, courtesy Great Barrier Reef Marine Park Authority staff, Copyright Commonwealth of Australia (GBRMPA)