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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.

Item Type:	Refereed Article
Keywords:	Primary productivity . Canal development . Microphytobenthos . Ecological impact assessment
Research Division:	Environmental Sciences
Research Group:	Environmental Science and Management
Research Field:	Environmental Impact Assessment
Objective Division:	Environment
Objective Group:	Ecosystem Assessment and Management
Objective Field:	Ecosystem Assessment and Management of Coastal and Estuarine Environments
Author:	Cook, SS (Dr Suellen Cook)
Author:	Roberts, JL (Dr Jason Roberts)
Author:	Hallegraeff, GM (Professor Gustaaf Hallegraeff)
Author:	McMinn, A (Professor Andrew McMinn)
ID Code:	54355
Year Published:	2008
Deposited By:	IASOS
Deposited On:	2009-02-18
Last Modified:	2014-11-07
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