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Nearshore Antarctic reef assemblages : influence of sedimentation and benthic irradiance


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Goldsworthy, Paul Michael 2010 , 'Nearshore Antarctic reef assemblages : influence of sedimentation and benthic irradiance', PhD thesis, University of Tasmania.

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Sediment runoff accelerated by human activities is known to be a major threat to
nearshore marine communities worldwide, however impacts of sedimentation in Antarctica
are largely unknown. Each summer at Australia's Casey Station, meltwater entrains
sediment from crushed rock roadways causing visible surface plumes in Brown Bay.
Observations during previous studies indicated a paucity of reef species in Brown Bay
compared to other bays in the Windmill Islands. Differences were attributed to two
possible factors: 1) elevated sedimentation rates resulting from human activities, and 2)
lower benthic irradiance caused by thicker snow cover overlying sea ice. This thesis
examines the potential impacts of sedimentation and benthic irradiance on shallow rocky
reef assemblages in Antarctica using both manipulative in situ and aquarium experiments.
Digital video transects quantitatively confirmed that reefs in Brown Bay supported a
significantly lower cover of biota, fewer total species and individuals, and fewer sponge
species compared to nearby 'control' bays. Recruitment to artificial substrata in Brown
Bay and 'control' bays was numerically dominated by spirorbid polychaetes and
encrusting bryozoan species after 13 and 37 months. Recruitment varied significantly
between bays, although overall fewer species and fewer bryozoan species recruited at
Brown Bay. More taxa recruited when sedimentation was experimentally inhibited in
Brown Bay (using Plexiglas shields), indicating sediment loads were hindering recruitment.
Aquarium experiments showed a 0.5 mm thick sediment layer prevented zoospore
settlement and early post-settlement growth of the brown alga, Himantothallus
grandifolius, and smothering of attached zoospores by a thin layer of sediment caused
reduced germ tube growth. Translocated individuals of red alga, Palmaria decipiens, in
Brown Bay and 'control bays' had thalli lengths 80 - 99% shorter after 12 and 36 months
compared to lengths at initial deployment. Reduced thallus growth was apparent even
when sedimentation was artificially reduced, indicating that factors other than
sedimentation influence the growth of adult P.decipiens. A clear effect of irradiance levels
on thallus growth of this species in the absence of sedimentation was subsequently
identified in aquarium experiments, and results correlated with the field observations.
Anthropogenically increased sedimentation rates in Antarctica were shown to influence
recruitment success of sessile reef taxa (flora and fauna), while benthic irradiance was
identified as a strong determinant of macroalgal distribution. Sound environmental
management of runoff accelerated by human activities in Antarctica is considered critical
for reducing impacts on marine environments, particularly in light of climate change
predictions for polar environments.

Item Type: Thesis - PhD
Authors/Creators:Goldsworthy, Paul Michael
Copyright Holders: The Author
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Copyright 2010 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2010. Includes bibliographical references

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