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

Second Advisor

Dr Gary Kendrick

Abstract

It has recently become dogma that reef systems arc a source of diversity to algal epiphyte communities in adjacent seagrass meadows. While this theory had not been tested, it was often cited as the reason for unexpected results in algal studies and marine pollution monitoring. This study examined whether reefs do in fact contribute to the diversity of seagrass epiphytes by testing the effect of distance from reef on seagrass epiphyte communities. The study was conducted in the vicinity of Carnac and Garden Islands and Parmelia Bank, off the coast of Fremantle, Western Australia. Three habitat types were selected as treatments, on reef (0m), seagrass meadow near reef (reef), and seagrass meadow distant from reef {>3000rn from reef), with the experiments replicated at four separate locations. The study consisted of two experimental components and descriptive sampling of epiphyte communities on natural seagrasses. Each component investigated a different stage in the recruitment process of epiphytes. Propagule availability was examined by collection and culture of propagulcs to determine their origin and whether reefs contributed algal propagules to seagrass meadows. Community structure was examined by studying the recruitment of epiphytes to artificial seagrass and by sampling communities on natural Posidonia sinuosa, to investigate whether distance to reefs influences the post-recruitment processes which determine community composition. Artificial seagrass was used in addition to descriptive sampling to remove the confounding effect of host variability.

The results of this study showed that epiphyte assemblages in seagrasses adjacent to reefs were different to those different from reefs, and that reefs were a source of propagules to seagrass meadows. Propagule availability varied with distance to reef. Epiphyte communities growing on artificial seagrass and natural seagrass also-differed. The same trend was evident for propagule availbility, recruitment of epiphytes to artificial seagrass and epiphytes on natural seagrass, where ordination patterns showed a significant separation of sites adjacent to reef from those distant to reef. The differences intensified post-recruitment, as shown by the tighter clustering patterns and increased spatial distance between habitats evident in ordinations. Biomass was significantly higher for sties adjacent to reef, which confirmed earlier findings that proximity to reef is confounding monitoring programmes. These differences suggest different pre-recruitment and post-recruitment influences for epiphyte communities near reefs and distant from reefs. Reefs can reasonably be expected to produce changes in environmental factors such as water motion, grazing and nutrients, which affect epiphyte growth. Additionally, reefs provide a source of algal propagules to seagrass meadows which can affect community structure.

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