Jeju's Endangered Corals Show Alarming 'Slumping' Amid Rising Sea Temperatures

Marine activists in Jeju have sounded the alarm after observing endangered gorgonian corals in severe distress, exhibiting symptoms of 'slumping' that mirror conditions seen in early 2024. Shin Soo-yeon, head of the marine civic science center 'Paran,' described the sight of drooping purple seafan corals (Jasaeksujimandra-mi) and dark red seafan corals (Geom-beok-eunsujimandra-mi) as eerily similar to the early stages of a significant ecological event.

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I saw drooping purple seafan corals and dark red seafan corals. It's very similar to the situation in early 2024 when coral damage was severe.

The phenomenon, termed 'slumping,' is a physiological response of gorgonian corals to combined stressors, primarily record-high water temperatures and prolonged periods of low salinity due to freshwater inflow. This stress damages the corals, causing them to droop and potentially detach from their substrate, leading to death. The area around Munseom island off Seogwipo, known as the 'garden of gorgonian corals' and a natural monument, hosts over 130 species of corals and is designated as a marine protected area.

During recent underwater surveys, activists noted that some corals were in the 'expansion, drooping, and hanging' stages of slumping, with weakened stalks precariously attached to rock faces. While the current situation did not reveal the widespread anomalies observed in August 2024, the high water temperature warning has persisted for eight consecutive days. The average water temperature in Seogwipo in July (24.8°C) is similar to previous years, but the average August temperature has risen significantly, exceeding 30°C in 2024, a nearly 4-degree increase from 2021.

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Slumping is a phenomenon where gorgonian corals sit down due to damage to their physiological functions due to complex stress from record high water temperatures and prolonged low salinity.

Experts warn that even if corals appear to withstand current temperatures, the prolonged heat in August poses a significant threat. Yoon Sang-hoon, a specialized researcher at Paran, noted that while coral species have varying tolerances, temperatures above 25°C are stressful, and above 28°C can lead to near extinction for some. The visual evidence of corals 'melting like ice cream,' as documented in 2024 and published in an international journal, underscores the severity of the threat.

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The decline of these corals, which form the base of the marine ecosystem by providing habitats and breeding grounds for various species, necessitates systematic observation and documentation. Kim Tae-hoon, a senior researcher at the Korea Institute of Ocean Science and Technology, emphasized that Jeju remains a crucial high-latitude habitat for diverse temperate gorgonian corals. He stressed the importance of accurate cause identification and field surveys to develop effective countermeasures against the impacts of climate change on these vital marine resources.

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In August, the average water temperature rose by more than 4 degrees compared to 2021, from 25.9 degrees to 30 degrees. While corals have different temperature tolerances, some species struggle above 25 degrees, and some perish above 28 degrees.