New ‘pregnancy-style tests’ can detect destructive crown-of-thorns starfish on GBR

A new testing kit created by researchers from Australia can detect the coral killing crown-of-thorns starfish in a similar way to a home pregnancy kit. Using a special dipstick researchers can detect microscopic amounts of their DNA at the surface, which could help control their destructive population outbreaks below.

A positive result on the new crown-of-thorns detection kit (photo by AIMS)

For well over 50 years the crown-of-thorns starfish (CoTS) have been a major destructive force for corals on the Great Barrier Reef. The enormous sea stars, who can eat their own bodyweight in coral every day, have undergone frequent and expansive population booms and left a trail of broken reefs in their wake. With additional stressors on corals, including warming waters, agricultural run-off, sedimentation, micro-plastics and acidification, removing these destructive invertebrates has been a top priority for conservationists. However, because of how hard it can be to locate the starfish and predict where their population outbreaks will occur, it has mainly been a losing battle. Now a new testing kit, very similar to home pregnancy tests, could be about to turn the tide by allowing researchers and citizen scientists track the sea stars in a fast, accurate and cost-effective way.  

Crown-of-thorns starfish

Named after the long, spiky and venomous spines that cover their entire body, the crown-of-thorns starfish (Acanthaster planci) are one of the largest and most successful sea stars in the world. Found on reefs in the Red Sea, Indian Ocean and Pacific Ocean, they can grow up to 35cm across and are second only to the giant sunstar in size. They are nocturnal hunters that feed almost exclusively on corals and can devour areas as large as a dinner plate every day. Like other starfish these coralivores feed by inverting their entire stomach through their mouth and digesting a thin layer of coral’s soft tissue, before sucking out the available nutrients from within.

A CoTS feeds on a plate coral on the GBR (photo by AIMS)

CoTS reproduce through a behaviour known as broadcast spawning, where several females and males release their eggs and sperm into the water column above the reef at the same time. This method increases the likelihood that eggs will become successfully fertilized and that they will not be eaten by predators on the surface, which allows them to rapidly increase their populations over short periods of time. However their numbers fluctuate highly and despite their high fecundity often remain low for years, but when they do increase in density they can be extremely destructive for individual reefs.

Population outbreaks on GBR

One of the places most commonly and severely affected by CoTS is the Great Barrier Reef in Australia, which has suffered multiple population outbreaks since 1962. What causes the sudden and explosive outbreaks in numbers is still unclear. Some scientists believe that the overfishing of one of their major predators, the giant triton, is to blame, whereas others argue that rising temperatures, ocean acidification and other stressors make corals more susceptible to the starfish and therefore have encouraged their growth. However it is unlikely that we will ever really know, as most research into the sea stars now focuses on how to remove them from reefs rather than how they became so successful.

Scuba divers physically removing CoTS from coral reefs

Whenever their numbers do increase significantly it almost always results in significant and permanent damage to localized reefs, which are already under threat from multiple other stressors. Therefore removing the CoTS is a top priority for GBR conservationists. Lots of different methods have been utilized to try and control their numbers, such as physically removing them from reefs, introducing new predators, poisoning them with specific ‘reef-friendly’ toxins and cutting them in half (which can actually backfire as they are capable of regenerating up to half their bodies). However none of these methods are very effective, because the main issue with controlling them is that locating individual starfish and predicting their outbreaks is extremely difficult. This is because they are often hiding within or under corals during the day and their juveniles can be less than a centimetre in size. This makes it very hard to find them and even harder to assess their numbers.

New testing kit

Thankfully a new rapid testing kit, developed by researchers from the Australia Institute of Marine Science (AIMS), could be about to change this by allowing for quick and accurate identification of CoTS from the surface. The lateral flow assay, or ‘dipstick’, can be placed in the water and, much like a home pregnancy kit, tells researchers if crown-of-thorns starfish are present on the reef below with a visible stripe. However, instead of hormones in urine, this dipstick shows the presence of tiny parts of genetic material released by the sea stars, known as environmental DNA (eDNA). It can detect levels as low as 0.1 picograms (0.0000000000001 grams!) meaning it should be able to detect any starfish on the reef below and maybe even from adjacent reefs too. The AIMS team recently released a new paper in the journal Environmental DNA, showing off their new kit and how it works.

Lead author Jason Doyle from AIMS shows off the full detection kit and disptick (photo by AIMS)

Stopping the spread

This new dipstick test created by AIMS is very exciting for GBR conservationist, not only because it rapidly identifies crown-of-thorns starfish, but because the cheap to produce and easy to use kit can be given to anybody. Lead author Jason Doyle, speaking in a press release, explains that “it’s the sort of technology we would love to get out to as many people as possible” such as fishermen, tourism operators and local citizens. He believes that the information people can gather will act as a ‘red flag’ allowing researchers and conservationists to maximise their time and resources in controlling the CoTS and providing an early warning for mass population outbreaks. This could potentially provide a much needed lifeline to the GBR by alleviating one its major stressors and giving its corals one less thing to worry about.

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