Managing the invasion of the long-spined sea urchin in eastern Tasmania
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Long-spined sea urchins are overgrazing Tasmanian rocky reefs
The long-spined sea urchin (Centrostephanus rodgersii) has relatively recently established in Tasmanian waters. This large sea urchin overgrazes seaweeds and invertebrates on rocky reefs, causing a change from highly productive and diverse animal and plant communities to ‘barrens’ habitat largely devoid of marine life. These barren reef areas are unable to support commercial fisheries for abalone or rock lobster. Sea urchin populations are able to persist on and maintain barrens habitat indefinitely. Thus, Centrostephanus poses a very significant threat to the integrity of shallow reef ecosystems, and associated biodiversity and fisheries, in eastern Tasmania.
This project is concerned primarily with assessing management options to reduce the risk of further barrens formation and, to some extent, with rehabilitating existing barrens. It focuses on population control of the long-spined sea urchin at meso and coastal scales through enhancing rock lobsters as key predators, and at a local scale by direct intervention by divers.
Invasion moving southward
The southward incursion of the long-spined sea urchin from NSW and its successful establishment in Tasmanian waters is the result of southward transport of larvae by a strengthening East Australian Current (EAC). Increased velocity of the EAC is the ultimate result of ozone depletion and climate change in the Southern Ocean. Evidence suggests that the sea urchin established in the Kent Group in Bass Strait in the 1960s and in northeast Tasmania in the 1970s. Long spined sea urchins have now been found in south west Tasmania with evidence of initial stages of barrens formation as far south as Fortescue Bay on the Tasman Peninsula. Extensive barrens, often covering several hectartes, are found at various sites between Eddystone Point and Maria Island, and can extend over a depth range of 5 m to 40+ m.
Management options
This 4-year project, funded by the FRDC, NRM and TAFI, is assessing options to manage the threat of the sea urchin at three scales:
At selected sites, the sea urchins will be smashed underwater by abalone divers while fishing, and sea urchin populations and development of barrens at these sites compared with nearby sites where no culling will take place.
Lobsters large enough to prey on the long-spined sea urchin will be translocated to areas (several hectares in size) closed to fishing. Sea urchin populations and development of barrens at these sites will be compared with nearby 'control' sites without added lobsters.
Computer modelling will be used to assess options of building densities of large lobsters (> 140 mm carapace length), as the principle sea urchin predator, at coast-wide scales.
Involvement of stakeholders
The long-spined sea urchin issue is considered such a high threat to the integrity of shallow reef systems in Tasmania that this project has seen the unprecedented involvement of a broad spectrum of stakeholders, including the rock lobster and abalone fisheries, recreational fishing groups, State marine managers, community groups and enforcement agencies, and scientists. Members of these groups form the basis of a steering committee to oversee the research directions of the project.
Funding for the project is provided by the Fisheries Research and Development Corporation (FRDC), theNatural Resource Management (NRM) Program, and the Tasmanian Aquaculture and Fisheries Institute (TAFI) and the School of Zoology at the University of Tasmania. The project is run through the School of Zoology and TAFI.
. The project is run through the School of Zoology and TAFI.
