Nearshore Antarctic reef assemblages : influence of sedimentation and benthic irradiance
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 v...
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| Format: | Thesis |
| Language: | English |
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2010
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| Online Access: | https://eprints.utas.edu.au/19905/ https://eprints.utas.edu.au/19905/1/whole_GoldsworthyPaulMichael2010_thesis.pdf |
| Summary: | 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. |
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