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

230
10.9
Recolonisation by D. antarctica on experimentally cleared areas
correaponded with the period of gmaete release (Fig. 10.1) 0
at 'l'autuku cleared in April, May and ,June ~Jere
by a dense sward of J)u:rv1:lZaea (greater than lOOD/m 2 )
less than 10 em long.
Areas cleared at. other times of the year, e,g ..
Areas
prornp,tly recoloriisdd
when plants were
after the fruit.ing
1-. ~
per :wd, were pom::ly k:Gcolon~sed the folloltt.i_ng season (less than 10/m-)
because a variety of other algae hCl.a covered most. of -the available
space, The pattern of ~e9rowth on areas cleared outside the fruiting
period is at first largely dependent on which species were fruiting
at tile time of clearing.
or Scytosiphon l~mentar.ia,
Opportunistic species such as Ulva lactuca,
if fruiting, quickly covered the cleared
areas. At the same time the ~esident flora spread, so that after
two or three years speoies of Ballia, PoZysiphonia, Chondri a and
especially articulated corallines had formed a tight turf that
effectively prevented the es'tablishroent of any la\\ln-like sward of
n~colon)_sing DuMJiUaea. Once the turf of other algae toJas established,
recolonisation by the kelp was largely res-tricted to patches scraped
bare after by loose rock and drifting debris.
After several years,
the recolonising DurviUaea will become sufficiently dense again to
shade out the turf or red algae. Some areas cleared du~ing the 1972/
1973 summer were still dominated by a predominantly coralline turf
in 1975.
On an experimental strip at Port St. Mary on the Isle of Man
where Filcus and AscophylZum ",ere cleared, it took seven years for the
seavlced flora to :return to something resembling its original
composition (Burxows and Lodge 1951).
My results suggest that on
areas cleared in summer it will take at leas i: the srun!'"c
length of time
for the DurvitZaea band to return to something like its original
state.
To obtain rapid regrmvth of D. antarctica it is necessary to
prevent the establishment of a thick red algal turf,
Consequently,
it is best to harvest the keJp immediately prior to, or during its
fruiting period.
to the end of winter (August).
antarctica appears to be
best times of thE: yea:c to harvest.
In New Zealand this is from autumn (March/April)
Since the standing crop of Do
in autumn, -that would be one of the
CUtting du.ring spring and
summer will almost. certainly result in 1:etarded recoloni,jilciono