Nipon Pongsuwan, from the Phuket Marine Biology Centre, said he initially thought the mass death might have been caused by toxins dumped in the water.
But after examination, he said, it was more probable that heavy waves had washed the sea urchins onto the shore.
“From our initial examination, we think this is a normal phenomenon in the monsoon season. Local fishermen told us that they had often see sea urchins washed onto the shore during this season,” he said.
But, he said, although the urchin deaths might be natural, the entire bay is threatened by two phenomena – poorly managed garbage disposal and soil run-off from property and resort development.
Waste management has been a major problem around some islands around Phuket, he said, with garbage being dumped in the water. Especially harmful are cans of insecticide, he said. “Just a tiny amount of insecticide [left in cans] can do severe damage to marine life,” Mr Nipon said.
He also called for more cooperation between public and private sector to control sedimentation around the island, particularly in Chalong Bay.
Sediment has been collected in the bay since the tin mining era. Although tin mining stopped decades ago, its role in aggravating sedimentation has been taken over by run-off from property development sites cleared of vegetation.
“Damage to the marine ecosystem in Chalong Bay has an tendency to be more severe [than in other parts of the island] because the bay is semi-enclosed, with Koh Lone blocking the seaward side,” Mr Nipon explained.
“We found the water in the bay is more turbid than in the past because the currents cannot flush the sediment from the area.”
Evidence of the damage from development, he said, is the degeneration of the reef in front of Koh Lone. The condition of the reef is now “deteriorated”.
Mr Nipon said he thought the source of problem might be poor implementation of Environmental Impact Assessments, with developers not giving enough attention to mitigating soil run-off from construction sites.
“We need more cooperation between public and private sectors to solve these problems,” Mr Nipon stressed. Although Chalong Bay is particularly affected, he said, “It’s not just Chalong Bay; the problem occurs around the island, which will cause serious damage to Phuket’s environment.”