Prior to his current position, A/Prof Johnstone served as deputy director of the Centre for Marine Studies at the University of Queensland for 5 years, as well as the Assessment and Monitoring theme leader in the Coastal CRC, and as a member of the scientific advisory committee for CRC Reef. He has a long professional history in coastal nutrient and ecosystem function research, as well as in the communication of science to the community, government, and private sector bodies. In addition, A/Prof Johnstone has a longstanding international reputation in his field, having spent approximately 20 years undertaking CZM research and project management in over 13 countries on behalf of government and international donor agencies including IOC-UNESCO, Sida, and the World Bank.
Within Australia, A/Prof Johnstone's work is focussed on the understanding of benthic habitats, with an emphasis on nutrient processes and dynamics in coastal ecosystems. This includes aspects such as the influence of land-based inputs on coastal ecosystem function and its influence on specific outcomes such as toxic algal blooms.