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A biological monitoring survey of reef biota within Bathurst Channel, Southwest Tasmania

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Barrett, NS and Oh, E and Meyer, L and Jones, D and Edgar, GJ (2010) A biological monitoring survey of reef biota within Bathurst Channel, Southwest Tasmania. Technical Report. University of Tasmania, Hobart, Tasmania. (Submitted)

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Official URL: http://www.imas.edu.au

Abstract

The benthic reef communities of Bathurst Channel represent an important feature for the ongoing management of Tasmania’s marine ecology and diversity. Containing a number of fragile deep-water invertebrate species growing at accessibly shallow depths, the reef habitats are both susceptible to impacts and of scientific importance. The foundation for this study was the continuing need for a practical, quantitative monitoring program which will provide information on species composition, species distribution throughout the channel, and detect any changes occurring over time. The survey, conducted in March 2010, collected digital image data from depth intervals ranging from the intertidal zone to 20 metres depth at 13 monitoring sites extending throughout Bathurst channel, and compared it to baseline imagery taken in 2002. The high resolution imagery collected in 2010 was used to create a descriptive catalogue of the biota observed, which can be used for future monitoring and species referencing. Species and substrate percentage cover in the photos was analysed using an easily repeatable point count method (CPCe) where data files can be stored and reanalysed. The information collected described the changes in species composition along Bathurst Channel, and thus provided some insight into the relevant environmental and biological factors limiting the distribution of algal and invertebrate species throughout the estuary. Results were consistent with previous descriptions of the community types within the Channel, showing that this system is inherently stable over these time frames. Patterns in assemblage distribution reflected strong species’ responses to gradients in tannin levels and salinity throughout the estuary, distance from the ocean and the strength of currents/mixing. Percentage abundances of key species and species groupings (e.g. lace bryozoans) between 2002 and 2010 data were also comparable, albeit with a few differences resulting from an improvement in image quality between surveys. One notable change was an apparent 50% decline in sea whip abundance at both Munday Island and Forrester Point at 5 metres depth. This is presumed to be a consequence of drought conditions leading up to the 2010 survey, reducing the tannin concentration to a point where algal growth became possible in this zone, smothering components of the invertebrate fauna. Ongoing monitoring will enable recovery rates to be determined, and improve our understanding of the natural variability of these fragile assemblages in a changing climate. The decline in sea whip numbers does indicate that there is a delicate balance between invertebrates and algae in the lower photic zone within the Channel, one that corresponds with the depth occupied by many fragile invertebrate species, and that this balance could be significantly altered under climate change scenarios that relate to reduced rainfall. Due to new image analysis protocols established during this study, and the development of high resolution digital photography since 2002, further surveys and analysis of data will now be more easily comparable using the same sites, depths, and the methods of analysis as established here. This will allow for the successful provision of reliable monitoring data to feed into ongoing management and conservation of the unique ecosystems found in Bathurst Channel.

Item Type: Report (Technical Report)
Publisher: University of Tasmania
Additional Information: Copyright 2010 University of TAsmania
Date Deposited: 20 Nov 2012 03:57
Last Modified: 18 Nov 2014 04:44
URI: http://eprints.utas.edu.au/id/eprint/15323
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