Impact of canal development on intertidal microalgal productivity: Comparative assessment of Patterson Lakes and Ralphs Bay,South East Australia |
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Authors: | S S Cook J L Roberts G M Hallegraeff A McMinn |
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Institution: | (1) School of Plant Science, University of Tasmania, Private Bag 55, Hobart, Tasmania, 7001, Australia;(2) Tasmanian Partnership for Advanced Computing, University of Tasmania, Private Bag 80, Hobart, Tasmania, 7001, Australia;(3) Institute of Antarctic and Southern Ocean Studies, University of Tasmania, Private Bag 77, Hobart, Tasmania, 7001, Australia |
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Abstract: | We assessed the potential impact of a proposed canal development in an estuarine sandflat at Ralphs Bay, Tasmania on intertidal
microalgal productivity and species composition, by comparing it over summer and winter seasons with a well- established (30 year
old) canal estate at Patterson Lakes, Victoria. Pulse amplitude modulation (PAM) fluorometry was used to generate a relative
measure of photosynthetic performance, which combined with microalgal chlorophyll biomass and irradiance provides an assessment
of potential primary productivity. We present a sophisticated mathematical model for calculating benthic microalgal production
and the contribution to total primary production, taking into account sediment light attenuation as estimated from sediment
grain size. Ralphs Bay had a total productive microalgal biomass of 44 mg chlorophyll a m−2 which was six times higher than Patterson Lakes, while the relative productivity of Ralphs Bay was four times greater compared
to Patterson Lakes where productivity was virtually absent in the subtidal zone of the canal waterway. Ralphs Bay exhibited
a more or less homogeneous spatial distribution of microphytobenthos biomass but this was subject to some seasonal variation
in species composition, abundance and productivity. By contrast, at Patterson Lakes biomass distribution, diversity and productivity
was highly spatially variable in the canal system in both seasons. Patterson Lakes exhibited 60% lower microphytobenthos species
richness than Ralphs Bay but little variation in species composition occurred between seasons in the canal estate. This suggests
that the dominant diatom species in Patterson Lakes, Pinnularia yarrensis, Gyrosigma balticum and Pleurosigma salinarum, are well adapted to the disturbance regime within the canal estate. The proposed canal development at Ralphs Bay is estimated
to cause a decrease in microalgal productivity by both reducing available marine substrate (66% reduction) and replacing productive
intertidal phytobenthic habitat with nonproductive canal substrate. These combine to cause a decline in productivity of 92%
with significant flow-on effects predicted for higher trophic levels such as migratory wading birds. |
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Keywords: | Primary productivity Canal development Microphytobenthos Ecological impact assessment |
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