Green Island and Kenting: Taiwan's Volcanic Coasts and Their Coral Reefs
Taiwan sits at a tectonic crossroads on the western rim of the Pacific, where the warm Kuroshio Current sweeps up from the tropics and washes the island's eastern and southern shores. Just north of the Tropic of Cancer, these coasts lie at the very edge of where reef-building corals can flourish, and yet they are surprisingly rich. Two places capture this meeting of geology and biology especially well: Green Island, a small volcanic outcrop off the southeast coast, and the Kenting area at the island's southern tip. Both are ringed by coral, and both owe their reefs to the same warm water and the same restless ground.
A young and restless island
Taiwan is geologically young, pushed up by the collision of the Philippine Sea Plate and the Eurasian Plate. That ongoing collision raises mountains, drives frequent earthquakes, and has left the warmer southern and eastern coastlines fringed with coral. The rock beneath the reefs tells more than one story. Around the Hengchun Peninsula, on which Kenting lies, much of the shore is uplifted coral limestone, the skeleton of ancient reefs now standing above the waterline. Green Island, by contrast, is volcanic in origin, a weathered cone rising from deep water. In both cases the living reef grows as a thin, sunlit veneer over a much older foundation, and the shape of the coast still guides where corals settle today. Understanding that layered history helps explain why the two coasts look and feel so different underwater, even though they share the same warm sea. Where the seabed is hard volcanic rock, corals cling to steep walls and boulders; where old limestone dominates, they spread over gentler terraces and ledges. The result is a coastline that reads almost like a cross-section of reef time, from the fossil reefs on land to the living ones just offshore.
Green Island: a volcanic outcrop ringed with reef
Green Island, known in Chinese as Lyudao, lies a short ferry crossing east of Taitung. It is a compact island, easily circled by road in an afternoon, and its steep volcanic flanks drop quickly into clear water. Because the island stands in the direct path of the Kuroshio, it is bathed year-round in warm, oceanic water with little of the sediment that clouds many mainland coasts. Fringing reefs wrap much of the shoreline, and the clarity of the water has made the island one of Taiwan's best-loved diving destinations. The same volcanic setting also produces one of the island's genuine curiosities: a seaside hot spring fed by heated seawater, one of only a handful of saltwater hot springs known anywhere in the world.
An ancient coral colony beneath the waves
Among divers, Green Island is famous for a single, remarkable coral. Off the island stands an enormous colony of Porites, a slow-growing stony coral, that has become a landmark in its own right. Nicknamed the "big mushroom" for its rounded, top-heavy shape, it is regarded as one of the largest and oldest coral colonies of its kind, with age estimates running to well over a thousand years. A colony of that size is not a single animal but a vast city of tiny polyps, each adding a fraction of a millimetre of limestone a year, so that the whole structure is effectively a living record of centuries of ocean conditions. Its survival depends on stable, warm, clear water, which makes it both a marvel and a barometer.
Kenting: uplifted limestone and southern fringing reefs
At the far south of Taiwan, the Hengchun Peninsula reaches into the meeting of three seas. This is the heart of Kenting National Park, established in the mid-1980s as Taiwan's first national park, and it protects both land and sea. The coastline here is a patchwork of uplifted coral terraces, sandy bays and rocky headlands, with fringing reefs growing along much of the shore. Sheltered bays such as Nanwan curve away from the open swell and offer accessible reef within easy reach of the beach. Because the peninsula is narrow and exposed on three sides, conditions can change quickly, and the reefs vary from calm, snorkeller-friendly shallows to current-swept slopes that reward more experienced divers.
The Kuroshio and the life it carries
The single most important influence on both reefs is the Kuroshio, the powerful western boundary current often called the Black Stream for its deep blue colour. Flowing north from the tropical Pacific, it delivers a steady supply of warm, clear water that lets corals grow far closer to the subtropics than they otherwise could. The current also acts as a highway for larvae, plankton and pelagic fish, connecting Taiwan's reefs with communities much further south. This is why the marine life around Green Island and Kenting feels tropical in character, with branching and plate corals, reef fish in bright shoals, sea fans on the deeper slopes and, in season, larger visitors passing through the blue. The Kuroshio gives, but it also ties the reefs' fate to the temperature of the wider ocean.
Pressure from heat, people and the shoreline
These reefs are not untouched. Like coral communities across the region, they have suffered bleaching in unusually warm summers, when heat-stressed corals expel the algae that feed and colour them. Kenting's reefs sit close to popular beaches and busy tourist towns, so sediment, wastewater and physical damage from visitors add to the strain. Nanwan is also known to marine scientists because a coastal power station there draws in and discharges seawater, creating a natural laboratory for studying how corals respond to warmer water. The lesson from decades of monitoring is consistent: corals here can be resilient, but their tolerance has limits, and recovery takes far longer than the damage that causes it. Careful management of tourism, water quality and fishing is what keeps these reefs alive.
Diving and snorkelling two very different coasts
For visitors, Green Island and Kenting offer complementary experiences. Green Island rewards those who make the crossing with exceptional clarity, dramatic volcanic topography underwater, and the chance to see the great old coral colony that has drawn divers for years. Kenting is far easier to reach and better suited to first-timers, with gentle bays where snorkellers can float over living reef only a few strokes from shore, alongside deeper sites for those with more experience. In both places the golden rules are the same: keep off the coral, control your buoyancy and fins, take nothing living, and choose operators who respect the reef. Treated with care, these are among the most rewarding subtropical reefs in East Asia. Timing matters too: the warmer months bring the clearest, calmest water, while the winter months can be windier and cooler, especially in the exposed south. Local dive centres know the daily patterns of current and swell intimately, and a short conversation before entering the water is often the difference between an easy drift and a difficult one. Going with people who understand the coast is part of diving it responsibly.
Explore on the map
Both of these reef systems, and the warm current that links them, are easiest to picture from above. Open the interactive map to find Green Island off Taiwan's southeast coast and the Kenting reefs at the southern tip of the Hengchun Peninsula. From there you can trace the line of the Kuroshio, compare the volcanic and limestone coasts, and use the reef markers to plan where to dive, snorkel or simply learn more about Taiwan's remarkable subtropical corals.