Islands on Land

Blue pool Tokaanu

Hoani, a hot spring at Tokaanu. Photo Credit: Jean Power.

Geothermal areas are unique habitats and ecosystems that challenge the survival ability of most life forms. Their physical characteristics include high temperatures, steep soil temperature gradients, exposure to steam, highly mineralised soils and waters, extreme pH, infertile soils, and the presence of toxic metals and gases.

Geothermal ecosystems have a longitudinal zonation, which means the plant and animal life changes with distance from the heat and geothermal fluid source. This makes these areas small “islands” of unique and specialised species and communities.

Aquatic Habitats

Hot pools & springs. Mineral waters journey through heated rocks to discharge naturally at the surface. Temperatures range from 30-100°C and pH from less than 1 (highly acidic) to 10 (highly alkaline). Depending on their chemical composition and gas content, these mineralised waters can be bubbly, salty, acidic, smelly or even flammable!

Waikite stream

A diverse range of plants grows in this geothermal microhabitat at Waikite. Photo Credit: Jean Power.

Geothermal streamsides. Microhabitats are created where hot and cold waters meet. This allows species, particularly those with tropical origins, to exist in areas that would otherwise be too cold.

What lives in or near warm water? Distinctive aquatic flora and fauna occur downstream from thermal springs. Closest to the high temperature water source (>60°C), aquatic communities are dominated exclusively by high- temperature microorganisms (bacteria and archaea). As the water cools downstream (<60°C),a diverse array of algae and fungi appear, and then soft-bodied organisms (invertebrates) begin to occur where temperatures are less than 50°C.

Terrestrial Habitats

Waimangu sinter fumerole

Hot spring at Waimangu. Photo Credit: Jean Power.

Fumarole margins & warm microclimates. Fumaroles are steam and gas vents. Constant steam allows frost-sensitive plants to survive at the fumarole margins.

Heated ground. Geothermally heated soils result from heat flowing through the ground that is released at the surface as steam. Ground temperatures (15 cm deep) can range from 40°C to over 100°C. Some flora species such as the prostrate kanuka have evolved very shallow root structures to avoid the heated and acidic soils at deeper soil depths.

Cooled, hydrothermally altered soils. Hydrothermally altered soils are often infertile.They have been changed by geothermal steam and become highly acidic, have low amounts of organic matter and phosphorus, and may contain toxic concentrations of metals and trace elements.

Fumarole Te Puia

Fumarole and sinter terraces at Te Puia. Photo Credit: Jean Power

What can live in or near heated soils? While microorganisms thrive in extreme temperatures, the hot conditions prohibit any Eukaryotes, including any plant life and most invertebrates (insects), from residing in the hottest thermal areas. However, a complex variety of specialised microorganisms, plants and insects readily colonise areas adjacent to these heated areas.

Cradles for Early Life

The unusual food webs in geothermal areas may mimic conditions of the Earth billions of years ago when life originated. It is generally thought that life (primordial microorganisms) began in environments adjacent to geothermal features full of gases and toxic metals!