A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...

70
from IVJLWS to a level between the highest LWN and MSL. Johnston
(1966:51) stated quite incorrectly that D. antapctica is a subtidal
species in North Auckland. The kelp may extend as far down as
ELWS, but I have never seen it growing on stahle rock in the I,mb ....
littoral.
D. wiZlana grmvS below D. antapctica in the lower littoral and
e)ctends several metres into the sublittoral. Holdfasts are rarely
found above MLWS and plants axe rarely emergent for more than. about
an hour. Because this species has such long stipes (often longer
tha.n 1 m) the laminae of many subtidal plants are partly emergent
during sp~ing tides. During nea_p tides, only the tips of stipes of
the uppermost specimens break the surface.
The vertical distributions of the two species are dete~lined
and influenced by many factors, some of ivhieh are described below.
(i)
Wave for>ce
It is well known that zones of intertidal org'anisms ar.e elevated
with increasing wave force (Stevenson and Stevenson 1949; Lewis 1964) .
The two Du:rvilZaea species are no exception. Both the upper and
lower limits of D. antaY'otica and the upper limits of D. wi l lana
become elevated with increasing wCI_ve force. It is not kno\Yn if
the lower limit of the latter species is elevated, though presumably
this is the case.
Beveridge and Chapman (1950) who worked at Piha, showed that on
the exposed west face of Lion Rock the upper limit of ~,e D.
antarctica zone was 2.02 m above ELWS j while on the more sheltered
northwest side it was nearly 1.0 m lower. Measurements I have made
on First and Second Slopes at Tautuku showed that on First Slope the
upper limit of the Do antapcticQ band sloped from LS9 m above ELWS
on the seaward edge to 0.89 m further inshore near tb~ channel (Fig.
5.10) . On the more exposed Second Slope, the upper limit of the D.
antapctica belt sloped from 2.09 m to 1.6S m above ELWS along 'the
gradient of decreasing wave force. The D. antarct1:ca band is elevated
greatly on cliff faces subject to strong wave action. On the cliff
illustrated in Fig, 5.9, the top of the D, antar>ctica band on the
south side Has 3.3 m above EU1S, whereas on 'the more sheltered northeast
side it \'las L 2 m above ELWS. At West Cape on the F).ordland
coast (see frontispiece) the top of the zone was at least 4 rn above
E.LWS. On Solander L wilson (pers. carom.) reported that D. antarctica
fJ':"onds were hanging down above him when he stood at low tide level.