A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...
A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...
A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
231<br />
Harvesters will not cut all small pla.nts"<br />
Probably only the<br />
largest specirnel1s \\li11 be selected, <strong>and</strong> their removal wU.l have<br />
the effect <strong>of</strong> increasing the gro\'Jth rate <strong>of</strong> small plants previously<br />
shaded in the l.\nderstorey (Pig. 8. fib} .<br />
They will not .grow as fast as<br />
recolonising plants <strong>and</strong> for reasons outlined in Chr~pter<br />
9 only a<br />
small percentage will survive.<br />
No cO'fo.)1\ercia1. harvester is likely to chip away holdfasts<br />
exposing the patches <strong>of</strong>. bare rock beneath. Yet holdfasts cover up<br />
to 20% <strong>of</strong> the toto.l .I':ock surface, <strong>and</strong> :t:ecolonisation is heaviest on<br />
old holdfast sites.<br />
If, when harvesting during the fruiting season,<br />
holdfasts are left, then a large area <strong>of</strong> the rock cannot be<br />
recolonised. It takes 4-6 months for holdfasts to rot away, so the<br />
bare patches <strong>of</strong> rock are not exposed until summer or autumn, whereupon<br />
they are pr~nptly<br />
colonised by such opportunistic species such<br />
as UZva Zactuea. If harvesting is carried out in summer~ then it<br />
is best to leave holdfasts" When they finally rot away the<br />
Durvi Uaea would be fruitiing <strong>and</strong> could recoloni se the bare patches<br />
<strong>of</strong> rock.<br />
It is pointless leaving stipes when harvesting. Neither species<br />
regenerate new blades from severed stipes, Sometimes D, wiZlana<br />
stipes heal over a.nd the la taral blades continue to grow, but in most<br />
cases both stipe <strong>and</strong> holdfast rot away_<br />
Leaving stipes only<br />
prolongs the rate <strong>of</strong> decay <strong>of</strong> holdfasts, <strong>and</strong> without their stipes,<br />
harvested plants are very difficult to hal1dle.<br />
All <strong>of</strong> the experimentally cleared areas in this <strong>study</strong> were<br />
bounded by virgin st<strong>and</strong>s <strong>of</strong> kelp.<br />
Gametes <strong>and</strong> zygotes only had to<br />
drift a fe\'l metres to recolonise the c'leared sites.<br />
The distance<br />
that gametes will drift is not known. Presumably sperms drift a long<br />
\oJay, but the sacs <strong>of</strong> ova when discharged from conceptaeles sink quite<br />
quickly (3-6 em per minute) <strong>and</strong> are unlikely to drifC very far.<br />
If all fertile plants are harvested from several kilometres <strong>of</strong> shore<br />
then there is no guarantee that ova are dispersed Nidely enough £01:<br />
all <strong>of</strong> the harvested ax:ea to be recolonised. In parts <strong>of</strong> Chile<br />
w·he.'Ce almos 12 0.11 large D, <strong>antarctica</strong> are ha.rvested for food (Appendix.<br />
5) recolonisation by the kelp is very slow {Pa.ine, pers. comm _} " Ova<br />
may onJy drift far enough to recolonise the margins <strong>of</strong> the harvested<br />
area with the resultant recolonisation <strong>of</strong> the rest <strong>of</strong> the area taking<br />
sevel:al years"<br />
Nei ther : time nor resources peL'mi t ted me to harvest several
Change language