One of the major biological surprises of the late 20th century was the discovery of a group of seabed organisms that live independently of photosynthesis-based food chains. Instead, they rely directly or indirectly on chemicals flowing from the sea floor.
Animals around vents
These creatures were first discovered in 1977 in the eastern Pacific where they were living in hot water around a hydrothermal vent (an underwater volcanic hot spring) several thousand metres deep. Since then, a number of hydrothermal vents have been discovered around New Zealand. Among the more conspicuous animals found at these sites are:
- at least two species of large mussel
- a large, predatory sea star, found nowhere else to date
- a number of species of blind shrimp
- two species of large tubeworm
- a pale eel-like fish
- crabs.
Life around methane seeps
Similar distinctive communities of seabed animals occur around underwater seeps of hydrocarbons (primarily methane). These cold seeps are found at the undersea margins of continents. At least 3 sites at depths of 900–1,800 metres off the East Coast of New Zealand are known to harbour living representatives of these communities. The dominant animals are shellfish (clams, a type of mussel, and limpets).
Chemosynthetic feeders
Animals that live around hydrothermal vents and cold seeps can exist there because of chemosynthetic bacteria. These synthesise food (sugars) using energy-rich chemicals such as hydrogen sulfide and methane. They are the primary producers within the vent and seep ecosystems. Some animals feed on the bacteria directly, while others have bacteria living on or in their bodies in a symbiotic relationship – the host animals get food and the bacteria gain shelter.