Climate change, ecological action, Uncategorized

Corals, Starfish & Robots

Coral reefs occupy a mere 0.1% of earth’s surface but accommodate a biodiversity that is almost on par with the rainforests. Apart from the immense biodiversity, they also provide a multitude of services from coastal protection, providing habitat and food, medicinal values, water filtration, carbon sequestration to building islands. The Great Barrier Reef is the world’s largest coral reef. The 2,300km-long ecosystem comprises thousands of reefs and hundreds of islands made of over 600 types of hard and soft coral. A coral reef is typically made of very small minute polyps in association with algae called zooxanthellae. Coral polyps secrete calcium carbonate exoskeleton from the underside of their skin that accumulates over years to form coral reefs. They grow at different rates varying from 5mm per year to 20 cm per year. Hence coral building is a very slow process taking years to form. The geological record indicates that ancestors of modern coral reef ecosystems were formed at least 240 million years ago. Most established coral reefs are between 5,000 and 10,000 years old.

These magnificent and ancient superorganism is facing threats that it has never encountered before. Climate change resulting in coral bleaching and constant recurring of natural disasters is something that we have been hearing for a while. But a new threat has been added to the list. The picture coral reefs invoke in our minds is one that is colourful and crowded with fishes and organism of every colour and design imaginable. A starfish with 14 legs covered with thorns may not look out of place, but these organisms are one of the major reasons of coral deaths after hurricanes and coral bleaching. These starfishes are called Crown-of-thorns starfish a.k.a. COTS (Acanthaster planci). In the 1970s on the northern Great Barrier Reef, a COTS outbreak occurred that lasted eight years. This outbreak peaked with about 1000 starfish per hectare, leaving 150 reefs devoid of coral, and 500 reefs damaged (Dixon, I. 1996). In the Togian Islands in Central Sulawesi, Indonesia, over 80% of coral on a reef was destroyed by a COTS outbreak (Fraser, N., B. Crawford, and J. Krusen. 2000).

What is a COT outbreak

COTs are natural members of the coral ecosystem. They normally feed on fast-growing coral colonies providing space for slow-growing colonies, thus regulating the coral ecosystem. The can grow up to 80 cms in diameter and feed by extending their stomach over the surface of the encrusting algae and digest the tissue. The natural density of COTS is 6-20 km2 which is less than 1 per hectare (Moran, P.J. 1990). An outbreak is usually defined as 30 or more adult starfish per hectare on reefs (Dixon, I. 1996), or when they reach densities such that the starfish are consuming coral tissue faster than the corals can grow (AIMS, 2012).

What causes a COT outbreak

Though it might seem like the organism is at fault, the problem has various underlying reasons and not surprisingly, all of them are anthropogenic. The major two reasons behind the increasing number of COTs are; firstly, increased phytoplankton blooms that in turn increase the survival rate of the larvae. The increased phytoplankton blooms can be accounted to their increased nutrient availability due to elevated effluent discharge from sewage and agriculture into oceans. For example, in the Great Barrier Reef, doubled concentrations of large phytoplankton were linked to nearly a 10-fold increase in larval development, growth and survival of COTS (Fabricius, al., 2010, Birkeland, C. 1982, Brodie, J. et al.,2005). Secondly, over-fishing has stripped the coral reef of all the major natural predator of COTs resulting in a tropical cascade leading to an unchecked population explosion of COTS (Bradbury, R. 1991).

Control of COTs

Several methods have been developed to control COTS. The methods include taking the starfish ashore and burying them, injecting compressed air, toxic chemicals, bile salts and vinegar, baking them in sun, suffocating them with fresh water and so on an so forth. The mechanical methods are labour intensive and hence expensive. Thus they are deployed only in regions of high socioeconomic and biological significance. Thus conservationists have been heating their brains to come up with better control measures (Rivera-Posada, J., et al., 2014)

Robots to the rescue

Make way for COTSbot, an underwater COT assassin robot, Dr Matthew Dunbabin of the Queensland University of Technology has been working on for the last 10 years to take over the meticulous task. COTSbot can cover up to 14 kilometres (8.7 miles) of reef a day, taking out hundreds of starfish without harming other species. This innovative technology by humans could be the answer to the COT crisis caused by humans. Looks like the robots would take off the Crown of Thorns from the Coral reefs, both figuratively and literally!!

The technology along with other conservation measures including controlling over-fishing and reintroduction of natural predators might save the largest organism on earth from COTS that cause about 40% of its death. Perhaps this technology could pave way for further innovations to control other ecological instabilities including invasive alien species.

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