Swamp, Bog, Marsh or Fen?
These terms each refer to a different type or class of freshwater wetland. Acidity and chemistry vary between wetlands, and result in distinct kinds of dominant vegetation.
Technically speaking, Mangarakau is mostly a swamp, but it also contains marsh, fen and lakes. These drain into Te Tai Tapu marine reserve.
Mangarakau is home to a wide variety of plants, ranging from terrestrial trees to aquatic plants.
The wetland covers about 350 hectares, of which half is owned by the Department of Conservation. The Trust owns most of the balance. Within this area there are three dominant vegetation patterns.
Within this area there are three dominant vegetation patterns. The Gleichenia fern/manuka scrublands are on the drier soils, while the wetter areas are covered in rush and reed communities of Typha orientalis (raupo) and Baumea. Within these areas there are some small lakes where the endangered Myriophyllum robustum continues to survive. The reedlands also have a some rare plants, including the pink Ladies’ Tresses Orchid (Spiranthes novae-zelandiae).
The growing list of plant species includes over 30 species of orchids.
There are some areas of planted eucalypts and Tasmanian blackwood which are being controlled. Colonisation by introduced plants is kept in check by the Friends of Mangarakau members.
The swamp abounds with frogs and fish, including eels, banded and giant kokopu, inanga, koura, freshwater shrimp and Nelson Marlborough's only species of brown mudfish.
The part of the Whanganui Inlet which links to Mangarakau Swamp is a marine reserve and harbors 163 different estuarine invertebrates, more than in any other South Island estuary.
Native carnivorous snails, geckos, spiders and a wide range of insects can be found within the swamp ecosystem.
The swamp's inhabitants are vulnerable to introduced animals such as cats, dogs and mustelids.
Rats, stoats and ferrets are all capable swimmers, and trapping is regularly carried out to keep their numbers down.
The brown mudfish was the first mudfish to be discovered in New Zealand and was formally described in the 1860s.
It is the largest mudfish species in New Zealand reaching a maximum length of up to 175 mm.
The brown mudfish is well known for its ability to aestivate (remain dormant). It is often encountered at considerable depths when digging farm drains in swampy ground.