Fiordland Marine Environment
The environment below the water in Fiordland is as unique as its acclaimed landscape above.
Visitors are always amazed by the reflections of the mountains in the quiet waters of the fiords. What most people don’t know, is that underneath these reflections lies a very special underwater world.
The inner fiords have a uniquely high level of freshwater input. As the heavy rain washes through the leaf litter of the forest floor and into the fiords, it changes in colour and stains the surface water of the fiords. This rainwater is a dark tea colour and floats on the heavier sea water below making a freshwater layer that varies in depth from 5cm to over 10 metres deep. Below this low salinity layer the sea water is calm, very clear and relatively warm, with annual temperatures of 11-15°C. The reduced light below the surface creates a special place where species like red and black corals and seapens can live at much shallower depths than normal meaning that visitors, including recreational scuba divers, can easily experience this fragile underwater cliff world community that is as spectacular as a coral reef. The fiords are also home to brachiopods; clam-like animals that have remained relatively unchanged for over 300 million years.
There are fifteen main fiords, extending from Milford Sound southwards 200 kilometres to Preservation Inlet, having an average length of 21 kilometres between steep mountain walls rising to heights of 2,000 metres or more. The fiords all have broadly similar physical processes, but each fiord appears to have a distinctive assemblage of species on the rock walls. Marine algae increase in diversity and biomass as you move southwards, although it is only the outer third of the fiords that are rich in algae. There are also marked changes in the abundance and distribution of reef fishes with fiord region and depth.
Although the fiords extend to depths of over 400 metres, life peters out quickly in the gloomy depths. The reduced light restricts most life in the fiords to a narrow band around the rock walls extending to about 40 metres below the surface. The thin band of life extending around the coastline of all 14 fiords is estimated to make up a habitat area of only 42 square kilometres, less than the area of Bluff Harbour on the Southland coast. Below 40 metres the fauna of the fiord basins are low in diversity. On the muddy fiord bottom, heart urchins and tube worms predominate to depths of 200m, below this, bivalves, tusk shells, heart urchins and crabs occur in an environment similar to that found in depths of 1,000m in the open ocean. The outer Fiords are a high energy wave environment and the continental shelf is very narrow in this region. The fiord entrances and exposed outer coast contain marine biodiversity typical of southern New Zealand, similar to that found in coastal waters of Otago, Southland and Stewart Island. As well as creatures such as crayfish and fish, Fiordland provides a home for bottlenose dolphins (aihe), fur seals (kekeno), Fiordland crested penguins (tawaki), little blue penguins (korora), dolphins, and many types of whales that visit.
Bottlenose Dolphin photograph courtesy of Lou Hunt, Department of Conservation.
