The Marine National Park Headquarters (hereinafter MNPH), in collaboration with the Dongsha International Marine Research Station of National Sun Yat-sen University, has completed this year’s comprehensive survey of the coral reefs in Dongsha Atoll National Park. The average coral cover was approximately 62.3% on the outer atoll and 51.0% in the lagoon inside the atoll, both exceeding the coral reef health standard of 50%. However, the outer atoll monitoring stations showed a decline compared to the previous year, primarily due to significant differences in coral cover at the east-facing stations. This is likely caused by Typhoon Mangkhut, which passed from the south in mid-September, leading to prolonged wave impacts on the windward reefs.

Over the past few years, Dongsha Atoll National Park has established several fixed monitoring stations at different orientations around the outer atoll and within the lagoon to track coral cover and monitor long-term changes. As early as 2017, the north reef outer station dropped from 88.1% in 2016 to 61.3% due to typhoon impacts. This year, seven fixed stations were surveyed. Most stations remained stable, with the southern outer reef showing the highest coral cover at 80.6%, followed by the north reef at 66.9%, the west reef at 61.9%, and the east reef declining sharply to around 40%. The lagoon inside the atoll has very different hydrological conditions and coral assemblages compared to the outer reef. Concerns about coral bleaching due to high summer temperatures were alleviated this year because the numerous typhoons and tropical disturbances between July and September helped prevent prolonged high temperatures in the lagoon. Therefore, no severe bleaching was observed, and the average cover remained around 51%.

MNPH noted that the surveys of the eastern and southern stations were conducted shortly after Typhoon Mangkhut, allowing for timely observation of post-typhoon reef conditions. The typhoon, which formed in mid-September and moved from Luzon, Philippines toward Hong Kong, passed directly over Dongsha Atoll. Two weeks after the typhoon, surveys at approximately 10 meters depth showed that the southern reef was relatively unaffected due to terrain buffering and shorter exposure time, while the east reef, facing the wind, dropped from 76.3% to around 40%. Previously rich habitats with diverse coral types were severely damaged, with many branching and plate corals broken and only partially remaining, while large amounts of newly grown green algae were observed. As Typhoon Mangkhut approached from the southeast of the atoll and moved northwest, the east-facing stations experienced prolonged strong winds and waves, causing more significant impacts. Recent surveys have consistently shown that typhoons are a major factor causing fluctuations in coral cover on the outer atoll reefs.

MNPH emphasized that Dongsha Atoll, being remote and minimally affected by human activity, provides an excellent site to directly observe environmental changes. Recent surveys indicate that typhoons can cause substantial physical impacts to coral reef habitats, leading to reef damage. At the same time, the natural water disturbance from typhoons may prevent prolonged high temperatures in enclosed lagoon waters during summer, reducing mass coral bleaching and mortality. These events are part of natural ecological cycles. The post-typhoon survey images also allow for the observation of coral recovery processes.