Missing Tasmanian marine protected areas

Tasmanian needs a comprehensive, adequate and representative system of marine protected areas right now. With Tasmania’s marine environment under pressure from climate change, fishing and aquaculture, the need for a good system of marine protected areas (MPAs) has never been greater.

Marine protected areas have multiple roles. As with national parks on land, they can be places for recreation and contemplation. They can act as a refuge for species and habitats that are under pressure from human activities in the wider marine environment and are also a kind of insurance policy, providing a source of animals and plants to help repopulate damaged or overfished areas. They might even be useful sources of new stock to support fisheries.

One of the most important roles for marine protected areas in a changing environment is that they can provide baseline data to enable us to assess the impacts of human activities on natural environments. Making sense of how climate change, for example, is changing Tasmania’s marine ecosystem can be hard if changes are also occurring because of fishing. The expanding destruction of Tasmania’s rocky reef habitat by Centrostephanus rodgersii urchin barrens provides a good illustration.

 Source: http://soer.justice.tas.gov.au/2009.image/556/index.php

Source: http://soer.justice.tas.gov.au/2009.image/556/index.php

 

Barrens form when populations of the Centrostephanus rodgersii urchin increase to the point where the intensity of their grazing turns rocky reefs, normally covered by masses of kelp and other seaweeds, into barren wastes. Apart from the loss of biodiversity and rich marine habitats, the economic consequences are dire: urchin barrens cannot support recreational or commercial fisheries for abalone or rock lobster. Large areas of reef have already been lost in this way along Tasmania’s east coast. In some areas around St Helens, almost all the reef deeper than 12m has been destroyed. Once reefs have been converted to urchin barrens there is no reasonable likelihood of them recovering. Commercial harvesting of urchins for food, or simply culling them, are ineffective controls and, while there is the possibility of developing underwater robots to remove urchins, that technology is a long way into the future.  

Many pundits have suggested that the expanding barrens are a result of climate change alone. But experiments carried out in areas protected from rock lobster fishing and observations in Tasmania’s existing marine protected areas clearly show that the density of rock lobsters large enough (with a carapace length greater than 138mm) to prey on Centrostephanus urchins is the most critical factor. 

Research indicates that climate change does influence the spawning success of Centrostephanus urchins. But as these animals pump out huge numbers of eggs in any case, the controlling factor in the creation of urchin barrens is actually the density of rock lobster that are large enough to be able to successfully prey on the urchins and therefore control their numbers. Unlike global climate change, the size of the rocklobster population is something that can be controlled here in Tasmania by changing the management of the rock lobster fishery. MPAs have been vital to our understanding of the processes surrounding Centrostephanus urchin barrens, and this issue alone should be enough to justify having a proper system of MPAs in Tasmanian waters. 

In the current limited number of Tasmanian MPAs many habitat types are unrepresented; in four ofTasmania’s eight marine bioregions there are no proper no-take MPAs that prohibit fishing at all. While climate change poses the greatest potent threat to Tasmania’s overall marine environment, in the short term fishing is the most significant threatening process, so, to have the greatest value, MPAs need to exclude fishing. And we need protected areas representing all significant habitat types: because it is hard to understand how fishing and climate change affect a particular habitat type unless a reasonable amount of that habitat type is protected from fishing. 

If we had a comprehensive, adequate and representative (CAR) system of MPAs, as outlined in Tasmania’s Marine Protected Areas Strategy (a Tasmanian Government document developed by stakeholders who included government, scientists, the commercial and recreational fishing sectors and the Tasmanian Conservation Trust), we would have a better chance of identifying and quantifying the effects of fishing and climate change on the marine environment. This would give a much better chance of understanding what is happening in Tasmania’s marine environment and managing threats so that both the environment and fisheries can be protected during this period of unprecedented change.

Article and photo by Jon Bryan - TCT Marine Campaigner