University Of Tasmania
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Tasmanian seagrass communities

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posted on 2023-05-26, 02:28 authored by Rees, CG
Seagrasses are marine angiosperms that grow in sheltered coastal and estuarine water bodies. They play a significant role in coastal marine ecology, and are important breeding and feeding grounds for a number of fish species. However, seagrasses are vulnerable to the impacts of some human activities through their sensitivity to reduced light energy. This may be lowered by increased turbidity and sedimentation, or the excessive growth of algal epiphytes in response to raised nutrient levels. Five seagrass species occur in Tasmania, Amphibolis antarctica (Labill.) Sonder et Aschers., Halophila australis Doty & Stone, Heterozostera tasmanica (Marten ex Aschers.), Posidonia australis Hook. f. and Zostera muelleri Irmisch & Aschers., their presence or absence defining five zones around the Tasmanian coast. Most coastal areas were sampled., and seagrass beds located. When sampling these beds, the species, depth, density, substratum and presence of algal epiphytes were recorded. Using available aerial photography from three time periods (circa 1950, circa 1970 and the present)., seagrass beds in selected areas were digitally mapped into a GIS database using ARC/INFO. The sample site attributes were added to the database, and patterns of distribution and change analysed and mapped. The five seagrass species have distinct zonation patterns and distributions in relation to region, coastal formation, substratum and depth. An area of approximately 220 km\\(^2\\) was mapped, leading to speculation that from 400 to 500 km\\(^2\\) of sea grass rna y occur in Tasmania. However, the results of the analysis and mapping also indicate significant decline. Total loss has occurred in some areas. Decline is most pronounced in those parts of the State close to centres of human population and activity. There is a strong relationship between the seagrass decline in coastal areas and the presence and abundant of algal epiphytes. Ambient nutrient levels in some coastal water bodies are likely to be a major cause of seagrass decline. In this context, this thesis proposes some mechanisms for the management and protection of Tasmania's seagrass communities, and nominates representative coastal areas for possible reserve status.


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