Sea Urchins are real troublemakers. On the West Coast, the sea urchin population exploded when the sunflower sea stars that eat them were decimated by a wasting disease. Urchins devour kelp and they ate up 96% of the region’s kelp forests. Kelp forests serve as shelter and food for a vast array of marine life and kelp sequesters as much as 20 times more carbon than terrestrial forests.
A new study by researchers at North Carolina State University looked at the health of the coral reef in Honaunau Bay on Hawaii’s Big Island and found that ballooning sea urchin populations are endangering the survival of the reef.
Fishing in these areas has greatly reduced the numbers of fish that feed on sea urchins and urchin populations have grown significantly. There are areas of the reef where there are 51 sea urchins in every square meter.
The reef is already not growing at a healthy rate as a result of water pollution and overheating created by climate change. These result in a poor environment for coral to reproduce and grow, which leaves the reef unable to keep up with the pace of erosion caused by urchins.
Reef growth is measured in terms of net carbonate production – namely the amount of calcium carbonate produced over time. In the 1980s, healthy reefs in Hawaii produced about 15 kilograms of carbonate a year per square meter. The Honaunau Reef today shows an average net carbonate production of only 0.5 kilograms per square meter. The reef is growing very slowly and can’t keep up with urchin erosion.
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Huge sea-urchin populations are overwhelming Hawaii’s coral reefs
Photo, posted October 29, 2017, courtesy of Rickard Zerpe via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio
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