Crown of Thorns May No Longer be a Thorn in Scientists' Sides

By: Alexandrya Robinson, UHM MOP Student

In the Pacific Ocean off the coast of Australia, lies the Great Barrier Reef, a research focal point in understanding how coral reefs are impacted by climate change, ocean acidification, eco-tourism, invasive species, and even native species. The Great Barrier Reef currently faces a threat from a native species on the reef, Acanthaster planci, also known as the Crown of Thorns Starfish (CoTS).

This Indo-Pacific native species of starfish has venomous spines that give its name resembling the crown placed upon Jesus?s head during his crucifixion. The venom is a neurotoxin that can cause hemolysis and is dangerous for humans and marine creatures. As they crawl over the reef, A. planci eat coral polyps, making them a destructive force on the already vulnerable Great Barrier Reef.

One hypothesis that explains A. planci?spopulation explosion is the removal of the snails and fish that prey on young sea stars. Another hypothesis is that A. planci have higher reproductive success and much faster sexual maturity than previously thought. A single female can produce multiple millions of gametes per spawning session during the summer leaving large clouds of gametes in the water column. Their planktonic stage lasts a few weeks during which they feed on phytoplankton, growing relatively undisturbed until they mature at six months, when they switch to eating coral, and begin their own reproduction within two years. Even if the male and female gametes don? t meet, A. planci can reproduce by asexual cloning like many other echinoderms.

It is estimated that a single A. planci can clear up to 12 m2 of the soft polyp tissues of foundational reef corals like Acropora in a single year. Since the 1970?s there has been a race to find a solution to successfully removing large batches of this thorny menace. Recently a $9.8M project has been started with multiple collaborating entities. The Australian Institute of Marine Science (AIMS) has pioneered research using environmental DNA (eDNA) that is compared to known samples of body tissue samples, fecal matter, and gut DNA to find out when an organism is feeding and to identify their current life stage. eDNA is incredibly valuable and much cheaper than alternative options even with its limitations based on environment quality, organism DNA shedding rate, small segmentation of DNA, DNA ease of movement from one place to another, sampling ability, and the fact DNA degrades much faster in warmer climates which is the primary area where A. planci lives.

CoTSControl Innovation Program (CCIP) was founded on the idea of using eDNA for earlier detection and treatment of the larval stages of A. planci before they mature and begin to eat coral. Methods of managing CoTSpopulations include the use of robotics to identify A. planci genetics, eDNA sampling for monitoring, pheromone targeting, and even the introduction of natural predators such as the giant triton snail that can eat adult A. planci. Other marine species which are naturally immune to the toxins produced by A. planci and can eat their adult bodies include the M?ori wrasses, starry toadfish, titan triggerfish, pineapple trigger, and harlequin shrimp. Young A. planci that are still soft can be eaten by crabs, shrimp, and marine worms. These efforts are highly valuable because they are more efficient and prolific than previous human interventions such as removal and patrol of the over 2,300 kilometers of the Great Barrier Reef. However, direct removal should not be completely discounted as shown by the work of the Cook Islands younger generation who hunt

A. planci and use the bodies of the starfish as fertilizer as a part of the K?rero O Te ?? rau?s initiative to maintain self-reliance for food sources. All together these efforts make up the future of Acanthaster planci control and management and work to preserve the reef flats in the Indo-Pacific for future generations.

By:Sarah M cGhee,UHM M OPStudent