October 8, 2012
Scientists May Have Found A Way To Cut Down On Crown Of Thorns Starfish Invasions
Alan McStravick for redOrbit.com - Your Universe Online
The farmer and the casual gardener know the damage that can be done by an outside pest. Through chemical and organic (for the more eco-conscious among them) pesticides, they are able to eradicate the small predators that threaten their ecosystem. But just how do you effectively clear out a pest when its attack is underwater?
“A Crown of Thorns outbreak can destroy from 40-90 percent of the corals on a reef. Over the past 50 years it has caused more damage than bleaching,” said Dr Jairo Rivera Posada. “There were massive outbreaks in many countries in the 1960s and 1980s — and a new one is well underway on the Great Barrier Reef.”
During the more severe outbreaks, as a result of severe food shortages, the COTS will eat practically any and every variety of coral species present on their host reef. The younger COTS seek out encrusting algae as a food source. This is usually located on rocks and rubble in and around the reef structure.
Evidence has shown that the COTS is primarily nocturnal in nature, however, some larger individuals have been seen feeding during the day. The feeding method the COTS employs is called eversion. This process involves the gastric folds of the stomach membrane being forced out through the mouth of the starfish, being turned inside out in the process, effectively smothering the coral. Digestive enzymes are then secreted onto the coral and the digested tissue of the prey is consumed externally. The COTS is not typically social when it is dining. However, during outbreaks, they have been witnessed congregating in large groups.
It´s also important to note the breeding habits and success of this creature to understand how the outbreaks can occur. The COTS breeding season is between December and April. Theirs is a sexual reproduction, where the eggs and sperm are released into the water through pores on top of their central disk. Spawning can occur seemingly simultaneously by several of the group on a single reef structure. The female produces upwards of 60 million eggs in a breeding season, giving the COTS one of the highest rates of fertilization recorded among any invertebrates.
Add to this that the COTS have few predators once it reaches maturity. The juvenile starfish is more vulnerable because it will lack the signature spines of the adult. They are usually preyed upon by crabs, shrimps, annelid worms and fish.
When the COTS population is at normal or low densities, it functions in a symbiotic relationship with the reefs they inhabit. It´s only when the population experiences a drastic increase that the reef system is threatened. This is because the COTS can consume coral at a rate faster than the coral can grow.
As of now, there is only conjecture on why the COTS outbreaks occur. Some have postulated that overfishing has removed numbers of the few natural predators for this starfish. Others believe agricultural runoff to the oceans have aided in these population explosions, explaining that nutrients that wash into the oceans could be responsible for phytoplankton ℠blooms´ that would provide an abundant food source for the COTS larvae. One thing is known. These outbreaks have been occurring with regularity for thousands of years. However, the frequency and severity of these outbreaks have reached alarming levels in recent decades.
The JCU researchers have come across a harmless protein mixture that is used to grow bacteria in the laboratory. They have found that using this mixture can effectively destroy the COTS in as little as 24 hours. They believe that if they can show it is safe for other types of sea life, they could use their discovery to try to control outbreaks, if only to protect sites that are important for the tourism industry.
Inspiration struck Dr. Posada, a veterinarian turned marine researcher, when he was on the Lizard Island beach with Professor Morgan Pratchet of CoECRS. He began to think of the protein substance he was using in the lab, selectively culturing the Vibrio bacteria that naturally inhabit the starfish, and wondered if, in a higher dosage, they might actually damage their host.
Upon returning to their lab, they injected five starfish with the media culture solution. It consists of carbonates and proteins extracted from animal tissue. To say they were surprised to see the starfish rapidly fall apart and die would be an understatement.
“I was only hoping to impair their immune systems — so the fact that they died so quickly was a great surprise,” Jairo says.
Their investigation into their results showed the solution had caused the bacteria to bloom and attack the starfish. Add to this that the starfish suffered an acute allergic reaction to the unfamiliar proteins (mainly from cattle). And one more benefit was that the bacteria was able to easily spread to other starfish that came in direct contact or were near the infected individual.
It was the recognition of this ℠double whammy´ effect, states Professor Morgan, that showed this harmless protein mixture could lead the way to the development of a safe, convenient and fast way of killing Crown of Thorns starfishes.
“In developing a biological control you have to be very careful to target only the species you are aiming at, and be certain that it can cause no harm to other species or to the wider environment. This compound looks very promising from that standpoint — though there is a lot of tank testing still to do before we would ever consider trialling it in the sea.”
Outbreaks that occur in tourism-heavy locales are currently battled by employing a poison injection to the starfish that is administered by divers. It is a slow and tedious process, allowing a diver only approximately 40 injections per dive. Compare that to the relative ease with which this new solution can be delivered, via a single jab, and you see that divers can kill as many as 500 of the COTS in a single dive.
However, researchers say stopping an established outbreak of millions of the starfish is not feasible. They contend, even, that it is too late to stop the current outbreak.
“In the current COTS outbreak in the Philippines they removed as many as 87,000 starfish from a single beach. This gives you an idea of the numbers we have to deal with,” they stated. Other fresh COTS outbreaks have been reported from Guam, French Polynesia, Papua New Guinea and the central Indian Ocean.
The next step for the researchers is to put their protein solution through extensive testing to establish a technique that will be safe for use around corals, fish, other varieties of starfish, sea urchins and sea cucumbers.
They are also exploring other natural parasites and disease-causing organisms for controlling Crown of Thorns, as well as simple protein injections which trigger a fatal allergic reaction. However, any attempts to control these outbreaks will be futile without also addressing the root cause of outbreaks, including loss of starfish predators as well as increased nutrients that provide food for larval starfishes.