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

44.
(15)' Achelia variabilis (Fig 15.15)
Although not penetrating into the sandy area
off the mouth of Purau Bay Achelia, a small pycnogonid,
showed a tolerance to a wide range of habitats as it
crossed the shipping channel. Achelia was most abundant
near the northern side of the harbour, (see Fig 15.15)
where there was some cover such as low-growing algae
and bryozoans. The density of Achelia decreased rapidly
across the harbour·and it became rare around Ripapa
Is land.
(16) Sigapatella novaezelandiae (Fig. 15.16)
Sigapatella is a gasteropod, very similar to
Zegeierus tenuis in its mode of life. Both are normally
fou~d
attached to shells or ro€ks but Sigapatella
appeared to have a smaller overall range, being limited
to the area around the eastern tip of Quail Island.
As with Zegelerus,eggs are brooded in the mantle cavity.
Siqapatella is unusual in that it is a filter feeder
and does not need to move to feed.
, (17). ~ymene plebejus (Fig 15.17) .
Xymene is a small whelk, ubiquitous in the upper
harbour with the exception of the wave affected areas
near the low water mark in Governors Bay, Head of the
Bay, Charteris and Purau Bays. Densities were highest
in the area between the northern coast of Quail Island
and off the mouth of 'Purau, near Ripapa Island. Xymene
is carnivorous and it appeared from examination of
samples containing it that it fed on juveniles of
Chione, Maoriomactra, and Spisula. The valves of
these were penetrated by a small circular hole with
a. diameter of 0.75 millimetres that corresponded to the
expected size if Xymene was the predator.