The Kermadec Trench is an 8 km deep submarine trench east of the Kermadec Islands. Formed by the subduction of the Pacific Plate under the Indo-Australian Plate. The Kermadec Islands lie along the undersea Kermadec Ridge, which runs southwest from the islands towards the North Island of New Zealand and northeast towards Tonga (Kermadec-Tonga Arc). The four main islands are the peaks of volcanoes that rise high enough from the seabed to project above sea level. There are several other volcanoes in the chain that do not reach sea level, but form seamounts with between 65 and 1500 m of water above their peaks.
The Kermadec region supports significant populations of ocean-dwelling predators such as tunas, billfish and sharks, along with numerous species of whales and dolphins. On the sea floor, corals and reef fish thrive and in the depths of the trench itself, unique communities of bacteria, mussels, worms and shrimps have developed in the extreme conditions surrounding the hot water (hydrothermal) vents.
Because the Kermadecs are located at the northern limit of survival for many temperate species and at the southern limit for tropical species, the islands are home to a unique and rare combination of different species. There are records of 53 species of seabirds, at least 150 species of fish, 88 species of decapods (crabs, lobsters, shrimp), and many more species that are still to be described or even found.