The internal wave advantage
In the Wakatobi archipelago, the survival of the vast coral reefs depends on a powerful and seemingly counterintuitive phenomenon: massive, tidally-driven underwater waves. These are not surface waves, but large-amplitude internal waves (LAIW) that form between layers of water with different densities. As tides move across the ocean, they create these waves deep below the surface. When the waves reach the archipelago's steep underwater topography, they break upwards, forcing huge volumes of cold, nutrient-rich water from the depths up onto the shallow reefs.
This process creates a dramatic and beneficial shock to the reef system. Temperature loggers placed on reefs have recorded sudden temperature drops of up to 10°C within minutes as an internal wave washes over. This regular delivery of cooler water provides an important refuge from the rising sea surface temperatures that cause coral bleaching events worldwide. During a major bleaching event in 2010 that devastated reefs in other parts of Indonesia, Wakatobi's corals showed remarkable resilience, with only 5 to 10 percent mortality. Studies during the 2015-2016 El Niño event showed that internal waves reduced cumulative heat exposure on some Pacific reefs by as much as 88%.