Climate change triggers catastrophic overgrazing of Tasmanian reefs by sea urchins

Sydney, December 8 (ANI): In a new research, scientists have determined that a combination of overfishing and climate change are triggering catastrophic overgrazing of reefs by sea urchins in eastern Tasmania.

"When you get the two things happening together, it enables the urchin populations to build up to the point where they destructively graze," Professor Craig Johnson of the University of Tasmania told ABC News.

Scientists believe climate change is causing stronger winds in the Southern Ocean, which speeds up the rotation of the ocean system that drives the East Australian Current.

The faster current has caused warmer water to spread further south, to the waters off eastern Tasmania, according to Johnson.

He said that this is causing the water in the area to warm nearly four times faster than the global average.

The current is also carrying with it invaders from the north - the long-spined sea urchin from New South Wales waters.

"It is a really aggressive grazing species and it can just completely chew out the seaweeds and many of the other associated animals growing on the seafloor," said Johnson.

He said that this can create a habitat called a "sea urchin barren".

"The analogy is like taking a bulldozer to a rainforest - you clear it back to bare earth," said Johnson. "About 50 percent of the New South Wales coast looks like that right now," he added.

Johnson said that he and colleagues have previously found that the sea urchins are starting to form barrens in Tasmania and the race is on to stop these from spreading.

The team's latest research looks at the impact on reefs of the interaction between climate change and the decline in the number of lobster predators due to overfishing.

Johnson and colleagues carried out experiments inside and outside protected marine areas to show that fishing has made reefs more vulnerable to the climate-driven threat of the sea urchin.

"The urchins only become a problem when its key predator is overfished," said Johnson.

He said that while a lot of urchins are required to cause the barrens in the first place, reversing the process requires getting rid of nearly all.

According to Johnson, only lobsters of a certain size can eat sea urchins: They must be big enough to get their front pair of walking legs around a sea urchin.

"We're trying to determine the best way of increasing the numbers of these large lobsters that has the minimum pain to the industry," he said. (ANI)