Fertiliser runoff fuels current outbreak of crown-of-thorns corals
The crown-of-thorns starfish (COTS) have been attacking the Great Barrier Reef in recent years. The current infestation involves as many as four to twelve million COTS, eating away at the individual corals. Based on a WWF report, the number of COTS may reach 60 million in the next five years, making this the largest outbreak ever recorded.
Philipp Kanstinger, a marine expert from WWF, describes the coral loss as alarming, with the Great Barrier Reef already severely affected by coral bleaching, ocean acidification and cyclones. With the increasing frequency of COTS outbreaks, some portions of the reef may lose up to 90 percent of its coral cover.
Scientists believe that such outbreaks do take place, though rarely - perhaps once every hundred years. However, the recent outbreaks have been occurring so frequently that there is an outbreak every 14 to 17 years.
A major cause of the current outbreak is the increasing use of chemical fertilizers in agriculture, which leads to more fertiliser runoff entering the ocean. This in turn means more food for plankton, and the increased quantities of plankton means more food for the COTS larvae; thus, the exponential increase in the COTS population.
Every day, an adult COTS eats corals – as much as the size of a dinner plate – and leaves behind just the skeleton. Over the past 30 years, the Great Barrier Reef has lost half of its coral cover; the COTS have been responsible for 40 percent of this loss.
For the first time, the WWF has quantified the damage as 60,000 hectares of live corals in the last 30 years. This corresponds to an area that is as large as 84,000 soccer fields.
To eliminate COTS, divers patrol the reef regularly, injecting every COTS with poison. However, the magnitude of the problem is such that even if 400,000 of the offending starfish were removed in this manner, the impact would be insufficient to contain the spread. Another solution is the COTSbot, the underwater robot developed by Australian scientists to administer lethal injections to the COTS, as we had reported.
“In all previous measures, the starfish were removed individually. This is effective only in small areas in order to respond to a local attack,” said Kanstinger.
To restore the COTS to its natural cycles, we would need to prevent excessive nitrogen from agricultural fertilisers from being deposited into the sea. And for any recovery efforts to have an impact, this rate of runoff must be reduced by 80 percent in some areas, said Kanstinger.
WWF calls on the Australian government to put an end to nitrogen pollution and to support farmers in the transition to implementing environmentally-friendly farming methods.