Abstract. Australia was historically considered a poor prospect for subterranean fauna but, in reality, the continent holds a great variety of subterranean habitats, with associated faunas, found both in karst and non-karst environments. This paper critically examines the diversity of subterranean fauna in several key regions for the mostly arid western half of Australia. We aimed to document levels of species richness for major taxon groups and examine the degree of uniqueness of the fauna. We also wanted to compare the composition of these ecosystems, and their origins, with other regions of subterranean diversity world-wide. Using information on the number of 'described' and 'known' invertebrate species (recognised based on morphological and/or molecular data), we predict that the total subterranean fauna for the western half of the continent is 4140 species, of which~10% is described and 9% is 'known' but not yet described. The stygofauna, water beetles, ostracods and copepods have the largest number of described species, while arachnids dominate the described troglofauna. Conversely, copepods, water beetles and isopods are the poorest known groups with less than 20% described species, while hexapods (comprising mostly Collembola, Coleoptera, Blattodea and Hemiptera) are the least known of the troglofauna. Compared with other regions of the world, we consider the Australian subterranean fauna to be unique in its diversity compared with the northern hemisphere for three key reasons: the range and diversity of subterranean habitats is both extensive and novel; direct faunal links to ancient Pangaea and Gondwana are evident, emphasising their early biogeographic history; and Miocene aridification, rather than Pleistocene post-ice age driven diversification events

Integrative research has been the dominant theme in this Special Issue, demonstrated by contemporary examples of effective collaborations and solutions for the successful engagement of scientists in the policy and management arena. Evident in these papers is the increasing use of the term ‘best available science’ (BAS) as a basis for well-informed resource management decisions. The term is used to engender credibility and trust among stakeholders and promotes greater awareness, communication, involvement, transparency and understanding among research, policy and management communities. However, there remains no clear statement of the properties of BAS or guidance on its practical application in the decision-making process. We define the attributes that underpin BAS and examine the issues of uncertainty, risk and communication as key challenges to successful integrative management. We advocate an interdisciplinary process that facilitates understanding of discipline-based knowledge structures, articulates uncertainty and risk about the scientific information, and promotes engagement and trust among the generators and users of information. Ultimately, successful management of aquatic ecosystems will rely on scientists, managers and decision makers who have the skills and courage to apply the best science available and not wait for the best science possible.

As demand for consumptive use of groundwater escalates, the need for careful management becomes more pressing. Water reforms in Australia require explicit recognition of environmental needs in water resource plans, but subsurface groundwater dependent ecosystems (SGDEs) are rarely provided for. The ecological values of these sequestered ecosystems are not well documented and are readily overlooked. We review the biodiversity, ecological processes and ecosystem services of Australian SGDEs and highlight the ecological relevance of their connectivity with other ecosystems. A lack of attention to SGDEs in groundwater plans risks inadequate provision for environmental water requirements with probable impacts on ecological values, water quality and ecosystem goods and services in SGDEs and connected ecosystems. We suggest an ecohydrogeological approach to understanding the implications of anthropogenic disturbance on SGDEs based on their connectivity to other ecosystems and aquifer permeability. As well as a template for comparative research on the biogeochemistry and ecology of SGDEs in Australia and overseas, this conceptual tool has potential application in conservation planning, water resource assessment and environmental impact assessment.

I thank my principal supervisor, Professor Andrew Boulton, for his encouragement, support, guidance, and generosity with his time and knowledge. I also thank Dr Darren Ryder for his crucial on-campus supervision during the final stages of writing up, and his critical and insightful comments on the final draft. I am grateful to the Australian Research Council, the University of New England, Ecowise Environmental and the Wentworth Group of Concerned Scientists for generous financial support. Dr Peter Hancock patiently showed me the field work and laboratory processing of samples. I could not have done the field work without his help and that of Garry Bennison,

Worldwide, science–policy integration across jurisdictional boundaries is emerging as a major challenge to sustainable water management. The Australian national water reforms require statutory provision for environmental outcomes in water plans, informed by the best available science. Assessments of progress towards this goal of scientifically rigorous environmental water provision indicate that, despite a multiplicity of effort in aquatic research and management, the pace of reform has been too slow for adequate protection of aquatic ecosystems. Although there are significant knowledge gaps, these are not the only obstacles to effective application of aquatic science in water plans. Progress on environmental water reform can be enhanced by recognising the cultural differences between science and policy, and by integrating communication and policy development activities from the outset of every applied science research program. Cross-jurisdictional progress in sustainable water management requires a comprehensive water research and policy development strategy using a toolbox of techniques to harness the considerable expertise and knowledge of aquatic scientists, policy makers and water planners in an integrated program to deliver the aquatic science applications called for by the national water reforms.