Date of Award

1998

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr Paul Lavery

Abstract

A range of seagrass characteristics were assessed for potential use as indicators of ecosystem health. Shoot density, shoot width, maximum shoot length, above and below ground biomass, percentage canopy cover, leaf area index, leaf extension rate, meadow productivity, epiphyte biomass, epiphyte species richness, percentage of calcium carbonate in epiphytic material and percentage of nitrogen in leaf tissue were all measured in “healthy~ and unhealthy" Posidonia augustifolia meadows in Cockburn and Warnbro Sounds, from June through to August 1998. A questionnaire was used to determine which meadows researchers and managers in the seagrass ecology field in Perth perceived to be healthy or unhealthy. Seagrass meadows were then compared according to several indicator criteria, primarily whether they showed any differences between perceived healthy and unhealthy meadows. A second questionnaire was undertaken to obtain and understanding of which variables researchers and managers felt were important in formulating a perception of seagrass ecosystems health. These perceptions were then compared with the measurable data for each variable. This was to provide an indication of whether the decisions made and influenced by these people on the management of seagrass ecosystems are based on comprehensive and accurate information. The sites perceived to be healthy, corresponded with previous data on the region which indicated they were Jess nutrient enriched, had higher light attenuation and less phytoplankton in the water column than those perceived to be unhealthy. There were only two variables to show significant differences between the perceived healthy and unhealthy sites, maximum shoot length and above ground biomass. These two variables and only two others, shoot density and percentage canopy cover adhered to at least four of the six indicator criteria, with maximum shoot length adhering to all six. These results differed to the perceptions of researchers and managers, with the exception of shoot density and percentage canopy cover. Epiphyte composition and epiphyte biomass were the other two variables considered to be important in formulating a perception of the health of a seagrass meadow. Information from this study suggests that management of Posidonia angustifolia meadows should centre around the measurement of maximum shoot length and above ground biomass. The vastly different results obtained from the questionnaire suggested that current seagrass monitoring in Western Australia may be in adequate. Further study on monitoring Posidonia angustifolia and Western Australia's other dominant seagrass species is thus recommended to ensure management decisions are based on data that arc as close to reality as possible.

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