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

115
attached more shallowly. It is pertinent here to point out that
D. wilZana speci1nens \.,ith the greatest number of annual bands in
the lamina were almost always found grm·!ing in the deeper channels.
(c)
~~ffect of herbivores on mor~c;r.r:
Certd.in isopods, especially Arrrphiroidea faZaifer ThoUlpson, eat
DurviZZaea fronds.
They rasp away the meristoderm and part of the
outer cortex thereby injuring the surface of the plant. (Fig. 5,12£).
Holes may develop on the lamina. Nhere this grazing has been severe,
and these ultimately increase the degree of division of the lamina 0
Of greater importance is the effect that fish have on the morphology
of young Dur>viZZaea. Young D. anta1'ctica which recolonised
experimentally cleared areas at Kean Point, were. extensively grazed
by the green bone or butter fish CoridOdax t~llus Forster, and probably
by other species as well. I have. unconfirmed reports that species
of parrot fish (Pseudolabrus spp.) feed on DurviZZaea.
The numerous
bites which the fish take out of the laminae give the margins a
dentate appearance (Fig. 5.12a), and in some cases the entire lamina
and part of the stipe is eaten.
The lamina margin eventually heals
over, and the small points of tissue between adjacent bites grow to
form narrow thongs (Fig. 5.12b).
Where the entire margin has been
bitten, a fringe of thongs develops.
When D. antarctica plants are very small, limpets, especially
the large species CeZlana denti(Julata~
graze away substantial parts
of the frond, and thus influence the general shape of the lamina ""hich
develops.
Thus herbivores exert some influence on the degree of division
of DurviZlaea laminae. and are probably partly responsible for the
morphological variation found in areas where wave force is
remarkably uniform.
(d)
The effect of J1erp,odiseJUs on morphology:
This parasitic brown alga caUses considerable damage to D.
antarctica tissue (South 1974).
When the dark reddish brown patches
of the parasite dlsB.,Ppeai.' in the spring. the infected regions of the
lamina, and less commonly the stipe, begin to degenerate.
'J:hongs
break off, clOd holes may develop in the palmate region of the li:l.\"o.ina .•
Almost all the lamina may break away in heavily infected
leaving only a remna.nt of the palmate L·egion (Fig. 5