PORT HUGHES, Australia — Situated midway along the Great Southern Reef that spans Australia’s southern coastline, the waters off Port Hughes typically teem with life. The coastal hamlet northwest of Adelaide plays host to a multitude of coral, bivalve and fish species. But in late March, the largest and longest harmful algal bloom (HAB) in Australian history arrived to Port Hughes, depleting its waters’ rich biodiversity. The bloom had first appeared elsewhere off the state of South Australia’s coast a year earlier, causing eye and skin irritation and respiratory symptoms among beachgoers. Then, along with waves of acrid-smelling sea foam, scores of dead marine animals began washing ashore. In Port Hughes, the HAB’s impacts were most visible below the surface. The town’s wooden jetty had previously been one of the most consistent locations in South Australia to observe temperate species, said Stefan Andrews, co-founder of the Great Southern Reef Foundation, a conservation advocacy group. But by mid-April, when Mongabay joined Andrews on a dive, the site was drab compared with vibrant photographs taken in February and March. Under the jetty, sponges and corals that had previously adorned its pylons in a brilliantly hued mosaic appeared colorless. Apart from a short-headed seahorse (Hippocampus breviceps) — a “sign of hope,” Andrews called it — little life was visible in the murky waters. The reef, he said, had become quieter, lacking the sounds of snapping shrimp and other creatures that once played in the underwater soundtrack. “There’s a sense of loss when you…This article was originally published on Mongabay

JEJU ISLAND, South Korea — In April 2025, I zipped myself up into a thick wetsuit and inched down a steep, rocky ledge toward the gray-blue water encircling Beomseom, a small island off the southern coast of Jeju Island in South Korea. Then I leapt into the chilly sea and wriggled into my scuba gear while floating on the surface. In the water with me was Sanghoon Yoon, an adviser for Paran Ocean Citizen Science Center, a South Korean civil society group that advocates for the protection of the ocean. That day, Yoon was my scuba dive buddy. Yoon and I sank beneath the dangling legs of snorkelers into a watery realm of rocks and kelp. Once in deeper water, I encountered gelatinous stalks of soft coral. The polyps appeared purple, pink, red, and even orange, depending on the light. The islet of Beomseom off South Korea’s Jeju Island hosts colorful gardens of soft coral. Image courtesy of Paran. Sanghoon Hoon, an adviser to the Paran Ocean Citizen Science Center, dives among  corals in the waters off Jeju, South Korea. Image courtesy of Paran. The soft corals I saw that day were healthy. But in 2024, soft corals around Beomseom Island and other parts of Jeju experienced what scientists are calling a “slumping” event — and what Yoon describes as “melting” — which saw soft corals losing their shape, drooping, and even dying. The event was widely reported in local media and attributed to marine heat as Jeju waters hovered…This article was originally published on Mongabay