Cradles for baby corals designed to frustrate toothy predators such as parrotfish could be deployed as part of a drive to rehabilitate reefs hit by disturbance events such as coral-bleaching.
Scientists from the Australian Institute of Marine Science (AIMS) and James Cook University (JCU) have designed the devices to help prevent reef-grazing fish from eating the tiny corals before they can become established. The corals are particularly vulnerable in their first year of life.
Field-testing indicated that the cradles worked best if made with protrusions, which reduced the numbers of fish-bites by providing small crevices in which the corals could develop undisturbed. The level of protection was similar to that afforded by caging the entire coral.
The AIMS scientists have been collaborating with others from the Reef Restoration & Adaptation Program (RRAP) to research the rearing of corals in aquaculture facilities such as the National Sea Simulator at AIMS Townsville. The coral larvae settle on tiles that are slotted into the devices and taken to be positioned on the Great Barrier Reef.
“Young corals need all the help they can get in their early years because mortality rates are high,” says Taylor Whitman, lead author of a new study of the devices. “Designing devices that can help boost their survival is just one of many aspects of reef rehabilitation we are studying at AIMS.
“We need to find solutions that are effective at reducing the risk of predation on seeded corals, while also providing some access so the fish can graze and maintain the balance between the coral and competitive algae that also grow on the devices.
“We need to look at solutions that are scalable and not too labour-intensive, while taking into account the differing environmental conditions on the reef. It’s a complex challenge!”
The team spent eight months seeding nearly 350 devices harbouring baby corals and coral microfragments onto Davies Reef, near Townsville. Some tiles were unprotected, others caged off and others partially protected by cradles with built-in protrusions.
The devices were checked after two days, three months and eight months for grazing marks and mortality, with data on the biological and environmental conditions of the reef recorded.
Unprotected corals tended to be eaten within 24 hours. The cradles with built-in features were found to offer a simple, effective way of reducing grazing pressureand were cheaper and more scalable than cages.
“The orientation of corals in devices also had a major influence on survival,” pointed out Whitman. “Coral larvae often preferentially settle on vertical surfaces to reduce the impact of environmental conditions like high light and turbulent water flow.
“Our study shows that this vertical orientation can also provide shelter to corals from grazing fish. We found more corals alive in side-facing than top-facing orientations, and under certain ecological conditions, some vertically positioned corals survived without protection.”
The seeded corals also thrived better in those areas with abundant algae or hard corals that offered alternative food sources to the parrotfish.
“These coral-seeding devices are game-changing, as they are designed to be deployed from the surface and without divers across large areas of reef,” said RRAP executive director Dr Cedric Robillot. “It completely transcends current notions of coral reef repair, which are mostly done by hand across small areas.”
RRAP, a partnership between the Australian government’s Reef Trust and the Great Barrier Reef Foundation, provided primary funding for the study, which has just been published in Scientific Reports.
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