Remote and rugged, the inner reaches of the 14 fiords (also spelt fjords) of south-west New Zealand are unique. Fiordland’s climate, vegetation and topography have combined with oceanic influences to create habitats and biological communities that have no counterpart anywhere in the world.
The fiords were carved out of the mountains by massive glaciers some 20,000 years ago. When the glaciers melted, vast quantities of rocky debris were left at the entrance of each fiord. These mounds formed a partial barrier when the sea level rose 6,500 years ago, and today they restrict the flow of sea water in and out of the fiords. Within each fiord, the circulation of water is confined to the top 20–40 metres; deeper waters may remain undisturbed for years.
Damp and dark
Fiordland is one of the wettest places in New Zealand: over 7.5 metres of rain falls on this precipitous landscape every year. Huge volumes of water, discoloured after passing through native forest and layers of rotting leaf litter, flow down into the fiords. This yellowy brown fresh water forms a layer above the sea water that fills the fiords, and reduces light levels, allowing only greenish light to penetrate.
Narrow band of life
Steep sides and a thick layer of fresh water restrict most life in the fiords to a narrow band around rock walls down to just 40 metres below the surface. The habitable area is only about 46 square kilometres; much smaller than the harbours at Manukau (370 km²) or Wellington (77 km²).
It is this reduced level of light that makes the fiord waters so special. Green light is not very effective for photosynthesis and consequently there is only limited seaweed growth on the walls of the fiords. With less competition for space from seaweeds, encrusting and sessile animals like sponges and corals flourish on the underwater walls.
Near Fiordland, the continental shelf falls away sharply and a number of deep-water animals are carried from the Tasman Sea into the dark sheltered waters of the fiords. Here, conditions are similar to those of the deep ocean, and species such as black corals, sea pens and lampshells thrive on underwater cliff walls. Scientists label the phenomenon of animals surviving at depths much shallower than their normal range ‘deep water emergence’.