The Hawaiian Trough, otherwise known as the Hawaiian Deep, is a moat-like depression of the seafloor surrounding the Hawaiian Islands. The weight from the Volcanic Island chain depresses the plastic Lithosphere that is already weakened by the underlying thermal hotspot, causing subsidence to occur. The location with the greatest rate of subsidence is directly above the hotspot with a rate of about 2.5 millimeters per year. The Hawaiian Trough is about 5500 meters deep. The subsiding lithosphere is balanced out and through the concept of isostasy a part of the crust surrounding the trough is levered upwards creating the Hawaiian Arch. The Hawaiian Arch extends about 200 meters above the surrounding ocean floor, and contains tilted coral reefs.
The coral reefs in the Hawaiian Tough are described as mesophotic coral ecosystems, which can be found between 100 and 500 feet below sea level. 43 percent of fish species documented at the mesophotic reefs are unique to the Hawaiian Islands. At Maui's 'Au'au channel the largest uninterrupted mesophotic coral ecosystem was discovered, with an area larger than 3 square miles. These reefs contained many stony, reef building coral that belong to the genus Leptoseris, which are adapted for deep water environments. These coral environments are not greatly understood because the great depth where they exist make exploration difficult.