The benthic ecology and community structure in Lyttelton Harbour ...

25.
SECTION 3
FAUNA
3.1 INTRODUCTION
Biogeographically,Lyttelton Harbour lies in the
Cbokian province of New Zealand, comprising the Southern
part of the North Island and the northern half of the
South Island.
It is a mixed cold and warm water region
'with the subtropical convergence oscillating seasonally
about the~Btitude
of Kaikoura.
3.2 The ben~hic environment in the harbour
Mention has been made of the disturbance of
sediment in the upper harbour areas by swells with a
wave base of 3-4 fathoms (Section 1.2.2). Under extreme
conditions most of the water'in Governors Bay, from a
depth of 4 metres to the shore, resembles liquid mud.
The only exception to this is where currents are flowing
into the bay along the northern coast of Quail Island.
Elsewhere in the middle harbour the visibility averages
about 0.5 metres, indicating a constant moderately
high suspended sediment load.
Under normal conditions
this improves to about one metre visibility towards the
I
heads.
3.3 Hydrology
There is a large annual range of temperatures in
the harbour. In 1970 the variation was from 70C to 19 0 C
(see Fig.3). There are also quite large local variations,
particularly in Governors and Charteris' Bays where up
to 400 acres of mud flat may be exposed at low tide.
Th~ mud is heated in sunny weather 'and ~emperatures of