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

40 ..
well into Charteris Bayo . It also penetrates a shorl~.
distance into the muddy sediments of Purau Bay. As
with Halicarcinus there are concentrations about the
reefs at Ripapa Island and Quail Island. But unlike
Halicarcinus, Austromitra does not extend over the
dredged channel and the map shows the sharp cut off at
the edge of the dredged regionG Austromitra is present
in very smail numbers among the Chione beds but does
not extend out into the muddy middle harbour. There
may be a slight correlation between the appearance of
Austromitra and the growth of red alga. This is suggested
in Table 1 but not possible to prove at this stage.
There is a very large number of empty Austromitra
shells off the mouth of Purau Bay that may have been
transported by currents from the reef off Ripapa Island.
(9) Zeacolpus vittatus (Fig 15.9)
Commonly known as the ttturret shell", the
gasteropod Zeacolpus originally appeared to show a
very patchy distribution over much of the harbour.
Reconsi~eration
of the material showed that many samples
contained only empty shells. Where there were live
specimens they constituted on the average only ten
percent of the total shells taken. This percentage
was arrived at by"dissolving the shells away in 1M.
hydrochloric acid and relatin9 th~ number of carcasses
left to the original number of apparently occupied
shells. The final pattern showed a bias towards the
san~y sedi~ents, and a smaller number in the coarse
sand regions. There was a deep penetration into
Purau Bay, almost to the low tide mark. InPurau
Zeacolpus were surviving in very muddy conditions.
There was a scattered occurrence across the shipping