Lake Manapouri - Surroundings

Surroundings

The shoreline in the North and West of the lake remains substantially unaltered since deglaciation. Beaches have formed on the lake where rivers bring sediment to areas where the near shore relief is not too steep allowing pocket beaches to form. The beaches around the lake show many similarities to ocean shores. The shape of the lake funnels wind and waves down the long axis which leads to longshore transport or littoral drift of sediment and size selective sorting. There are however a number of differences to ocean shores. The short fetch length produces a narrow range of wave conditions and this low energy limits the size of sediment in transport. Large changes to the beach profile are induced by fluctuations in lake level, major fluctuations can drown beaches. The beaches on the lake develop a distinctive shelf profile whereby beach sediments grade lakeward into fine sand. The outer edge of the shelf is marked by a shelf break and a transition to organic-rich muds on a steep offshore slope. There are a number of different types of beaches including pavement beaches, gravel, mixed sand and gravel beaches and sand beaches.

The islands around Lake Manapouri are of varying size and isolation. Many of the islands contain virtually unmodified vegetation. However there is large diversity between islands in habitat biodiversity, with some islands being completely devoid of plants and soil and other rich in both. There is confusion as to some differences with some researchers finding that the area of an island plays a role in species richness with others find no correlation at all.Red deer have greatly modified much of Fiordlands' vegetation however only the two largest islands within Lake Manapouri contain introduced red deer while other islands are only occasionally visited by deer. The smaller islands around Lake Manapouri are extremely unique as they contain natural vegetation which has not been harmed by red deer, as the red deer have not been able to reach the islands. On these islands palatable plants as well as deep moss mat on the forest floor persist under the dense understory layers of the forest. The Australian bush-tail possum (Trichosurus vulpecula) is not present on the islands.