Tim Alexander

Responses of mobile invertebrates to reef habitat structure and fishing in temperate marine protected areas

Supervisors: Dr Russell Babcock (CSIRO), Dr Neville Barrett (TAFI), Dr Graham Edgar (TAFI), A/Prof Malcolm Haddon (TAFI), Prof Craig Johnson (UTAS)

Partly as a consequence of declining inshore biodiversity and perceived deficiencies in traditional single-species approaches to fisheries management, a growing number of "no-take" marine protected areas (MPAs) are being proclaimed worldwide. In tandem with this legislative activity, scientific research on MPAs represents a rapidly growing field. The declaration of MPAs represents a manipulative experiment at a vast, and ecologically meaningful spatial scale. However, to date published sampling designs have not effectively encompassed spatial, temporal and taxonomic scales of MPA effects. An appropriate design should include multiple MPAs, replicated sites inside and outside MPAs, multi-year comparisons with baseline data collected prior to MPA establishment, and a wide range of taxa.

An Australian study funded by ARC that fulfils these criteria is presently underway, involving collaboration between the University of Tasmania, CSIRO, NSW Marine Park Authority, WA Department of Conservation and Land Management, SA Department of Environment and Heritage, Tasmanian Department of Primary Industries, Water and Environment, and Tasmanian Parks and Wildlife Service. This large study involves monitoring of fish, invertebrate and plant communities in MPAs and adjacent reference sites through time.

Project outline and objectives:

This PhD project will be closely aligned to the ongoing ARC investigation. It will utilise a subset of field sites monitored in the larger MPA study, including sites distributed from NSW to WA, and around Tasmania. Results of experiments will thus be referenced against a large multi-year data set that includes density information on local fish and invertebrate predators and grazers, and percentage cover of plants and sessile animals.

The main focus of the project will be the investigation of effects of predator size and abundance on assemblages of juvenile and cryptic invertebrates, particularly with respect to how these relationships are influenced by the physical complexity of reef habitat. A major aim will be to quantify effects of predation pressure on recruitment of invertebrate prey species. This is especially relevant for abalone where declining densities in some MPAs-possibly as a result of increased predation-could potentially lead to recruitment failure. The project will also include investigation of functional processes associated with the widespread phenomenon of decreasing urchin populations in MPAs.

In addition to 'natural' experiments involving the modelling of relationships observed in the field between predator and prey densities, and the rugosity of reef surface and fractal dimensions of crevices, artificial substrata collectors will be deployed to mimic a variety of natural crevice sizes. Effects will be compared between kelp forest and urchin barren habitats inside and outside MPAs.

The project has considerable practical relevance for fisheries management, including the creation of models that predict effects of habitat structure on the recovery of invertebrate species within MPAs following cessation of fishing. MPA locations presumably vary greatly in habitat quality for particular species due to variation in reef structure, with complex habitats likely to generally experience fastest and more intense responses to release from fishing pressure. Quantifying various aspects of substratum complexity and relating this to patterns of density and size-structure of mobile invertebrates including rock lobster, abalone and sea urchins will enable us to better understand biotic responses following the establishment of MPAs, and assist in site selection for future MPAs.