As coral reefs in Hawaii face challenges from warming waters, pollution, and rising sea levels, a surge in sea-urchin populations poses an additional threat. A recent study highlights the situation at Hōnaunau Bay, where overfishing has led to a significant increase in sea-urchin numbers. “Fishing in these areas has greatly reduced the number of fishes that feed on these urchins, and so urchin populations have grown significantly,” said Kelly van Woesik, a Ph.D. student at North Carolina State University and the study’s lead author.
Van Woesik reported finding about 51 urchins per square meter, one of the highest densities worldwide. These urchins consume coral reefs already struggling with slow growth due to pollution and climate change-induced water temperature increases. Previously healthy reefs showed carbonate production around 15 kilograms per square meter annually; however, current measurements indicate only 0.5 kg per square meter.
The study combined scuba diving data with aerial imagery to assess reef health. Van Woesik noted that maintaining an average of 26% coral cover is necessary for reefs to withstand erosion from sea-urchins, while shallow areas require nearly 40% cover.
Coral reefs provide crucial coastal protection by absorbing wave energy and support local economies reliant on marine life. The study emphasizes the need for better fisheries management to boost carnivorous fish populations that control sea-urchin numbers. “The reefs cannot keep up with erosion without the help of those natural predators,” van Woesik stated.
The research titled “Scaling-up coral reef carbonate production: sea-urchin bioerosion suppresses reef growth in Hawaiʻi” appears in PLOS One. Co-authors include Jiwei Li and Gregory P. Asner from Arizona State University.
