Seascape Ecology and Conservation: Connectivity and Reserves in the Western Pacific

Abstract

In response to the growing human population and our impacts on the environment, we design programs for conservation, restoration and rehabilitation to maintain and enhance productivity, biodiversity and ecosystem resilience. To ensure the greatest return on these investments, there is an implicit requirement for identifying disproportionately important species, processes and landscape elements as high-value targets for conservation and management. Connectivity is commonly favoured among these because it provides the mechanism for reserves to sustain exploited populations beyond their borders, and is critical for reversing the ecosystem impacts of trophic cascades. Few studies have, however, adopted a quantitative approach, like that provided under the framework of landscape ecology, to assess the value of connectivity in conservation. This conceptual division between the disciplines of conservation and landscape ecology must be bridged to better enable the management of healthy functioning ecosystems. This thesis used heterogeneous reef seascapes in Moreton Bay, Queensland, as a model system for examining the potential effect of connectivity in enhancing marine reserve performance. A positive effect of connectivity between mangroves and coral reefs was demonstrated on the performance of marine reserves, including effects on productivity, biodiversity and ecological resilience. This finding represents a critical first step in improving the integration of spatial ecology into conservation planning and assessment. This thesis then illustrates how neighbouring mangroves and seagrasses can exert different effects on reef fish assemblages and extends our current understanding of the role of connectivity in reef seascapes. This indicates that a reef’s position in the seascape can be of greater significance to the composition of fish assemblages than its area or complexity, and highlights the shortcoming of management approaches that focus solely on representing measures of habitat area, complexity or condition. Herbivorous fish play a key role in coral reef seascapes; by removing algae they promote coral growth and recruitment, and help to increase resilience. Habitat connectivity and reserves both influence herbivore populations and herbivory, but their potential interactive effects have not been investigated. This thesis shows that these factors can indeed exert synergistic effects on herbivore populations and grazing intensity, which facilitated a trophic cascade that reduced algal cover and enhanced coral recruitment and reef resilience on protected reefs near mangroves. The effects of reserves and connectivity for fish assemblages were then extended from a local to regional scale, by examining the potential interaction of these factors across the tropical and subtropical waters of the western Pacific Ocean. Habitat connectivity improved the performance of marine reserves across this region, and spatial variation in the magnitude of the reserve-connectivity interaction was explained by differences among reserves in the area of mangroves and reef, duration of mangrove inundation and distance to rivers. The management of heterogeneous inshore reef ecosystems as functional seascape units is considered necessary for preservation of critical interconnections among habitats. By further improving our understanding of seascape ecology and connectivity, and by incorporating this field of research into conservation ecology and decisionmaking, we should expect to have greater success in restoring exploited populations and the functioning of ecosystems.