Over the last decade, disease has emerged from being a long overlooked factor in natural communities to become an increasing focus for ecological research in terrestrial and marine ecosystems. There is also major concern that global warming and other anthropogenic stressors may be responsible for the spread of pathogens, enhanced virulence and decreased resilience of hosts. This project focuses on macroalgae or seaweeds, the dominant habitat-forming organisms in temperate rocky reef communities worldwide. They are the trees of temperate coastal ecosystems. Anthropogenic stressors can have dramatic effects on the health and persistence of large macroalgae and are responsible for extensive losses of habitat-forming algae. Importantly, declines in habitat-forming macroalgae not only impact the algae themselves, but have major effects on the diversity and abundance of associated organisms. During this project, we aim to characterise microbial communities associated with the surfaces of dominant seaweed species on temperate Australian coasts, from northern New South Wales, south to Tasmania and also along the western Australian coastline. Furthermore, we aim to identify potential pathogens associated with stressed specimens and quantify their abundance at different sites and different times and correlate microbial data with various physico-chemical information from each site and specimen. This work will provide baseline data on algal-bacterial associations on a latitudinal scale and may also provide information on the distribution and abundance of potential algal pathogens. We hope also to understand how different environmental conditions influence algal-associated microorganisms and predict how environmental change may affect interactions between these microbes and their hosts.