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Subtidal macroalgal studies in East and South Eastern Tasmanian coastal waters.

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Sanderson, JC (1990) Subtidal macroalgal studies in East and South Eastern Tasmanian coastal waters. Research Master thesis, University of Tasmania.

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Abstract

This thesis is concerned with (1) the introduced Japanese
macroalga Undaria pimzatifida in Tasmania and (2) the growth patterns of
major components of macroalgal communities at two sites on Tasmania's
coast, Bicheno in the east and George III Reef in the south The algae
studied were Macrocystis pyrifera, Ecklonia radiata, Phyllospora comosa at
both sites plus the red algal community at George III Reef.
Surveys ofUndaria in 1988 found that it inhabited
approximately 15 kilometres of the east coast from Triabunna southwards
to Lachlan Is. The alga is very fecund and smothers the bottom in 'barren'
areas particularly in sheltered waterways at certain times of the year.
Effects on the local biota are unknown but the environmental tolerances
of the alga reveal a potential distribution from Cape Leeuwin in south
west Western Australia to Wollongong on the New South Wales Coast.
Environmental parameters and growth rates were monitored at
George III Reef from 1985-88 and at Bicheno from 1987-88. Over the joint
period, there was little difference in temperature, saliitity and nutrients of
the seawater between the two sites.
In 1988, the water masses of the south and east coasts of
Tasmania were distinguished by unusually warm waters. In March, the
warm nutrient - depleted waters of the East Australian Current were
detected further south than usual and in winter, coastal waters were
relatively warm and nutrient poor compared to previous years (Harris et.
al1991).
For Ecklonia radiata, light appears to be the most significant
factor affecting the rate of increase in lamina length and thus production
at Bicheno and George III Reef. At George III Reef, high temperatures and to a lesser extent large swells negatively affect growth rates. It is postulated
that swell may be acting indirectly through its affect on the amount of
suspended particles in the water column and thus reducing light.
Productivity estimates suggest 1.8 kg wet wtfm2fyr at 14m depth at George
III Reef and 4.7 kg wet wtfm2fyr at 10 m. depth at Bicheno in areas of
continuous cover.
For Macrocystis, production appears to be best determined
from rate of blade production because change in length may be affected
extrinsically by factors of swell and light. Productivity of M. pyrifera at the
two sites suggests similar frond productivities of 6 kg wet wt/frond/yr. For
a typical density of 4 fronds per m2 of sea floor this results in estimates of
24kg wet wt/m2/yr weight. Macrocystis disappeared almost entirely from
both sites during the warm year of 1988.
For Phyllospora, regression of growth increment against
environmental parameters indicates light availability as the principal
factor affecting growth for most of the year though nutrients are likely to
limit growth in late summer. High rates of plant mortalities and lower
growth rates late in the study coincide with the incursion of the EAC and
the warm winter of 1988. The calculated production at George III Reef of
approximately 7.4 kg wet wtfm2 /yr at 7.7m depth compares with the
combined Phyllospora comosa and Ecklonia radiata annual production
figure of 4.8 kgfm2fyr at Bicheno at 10m depth.
For the red algal community at George III Reef, filamentous and
foliose species increasing in number in the summer and outside of the
Macrocystis canopy. The presence of the Macrocystis canopy results in a
halving of the red algal biomassfm2.

Item Type: Thesis (Research Master)
Keywords: ecology, Tasmania, macroalgae, Undaria, Macrocystis, Ecklonia, Phyllospora, marine
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Date Deposited: 27 Oct 2011 23:54
Last Modified: 11 Mar 2016 05:55
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