Most hadal habitats are found in which ocean?

Most hadal habitats are found in the Pacific Ocean.

The hadal zone occupies the deepest parts of the seafloor, principally within long, narrow oceanic trenches. The Pacific contains more of these trenches than any other ocean because its margins include extensive subduction zones, where dense oceanic crust sinks beneath another tectonic plate.

The Pacific is also the largest and deepest of the conventional oceans. Its major hadal regions include the Mariana, Kermadec, Tonga, Japan and Kuril–Kamchatka trenches. About 94% of the hadal zone is associated with subduction trenches, making the Pacific’s active plate boundaries especially important to the distribution of hadal life.

“Most” does not mean all. Hadal habitats also occur in other oceans, including the Puerto Rico Trench in the Atlantic and the Java or Sunda Trench in the Indian Ocean. These ecosystems are dark, cold and intensely pressurized, yet they support organisms such as amphipods, sea cucumbers, worms, microbes and a small number of specialized fish.