In August 2012 the Minister for Sustainability, Environment, Water, Population and Communities, Tony Burke, decided to list the ecological community ‘Giant kelp marine forests of south east Australia’, as endangered under the Environment Protection Biodiversity Conservation Act 1999. The listing recognises the severe decline, up to 98% in the case of one population, in the area of sea floor covered by giant kelp forests off Tasmania, which has been a cause of concern among scientists and conservationists for more than a decade.1 The original nomination in 2009, by Humane Society International, specified giant kelp forests in Tasmanian waters, but the listing also covers the occurrence of the community off Victoria and South Australia.
The ecological community meets the following criteria for listing as endangered:
· severe decline in functionally important species
· severe reduction in integrity across most of its range such that regeneration is unlikely in the near future, even with human intervention.
Giant kelp plants Macrosystis pyrifera literally form underwater forests, up to 35m tall, anchored on rocky substrate and reaching to the surface, where they form a canopy. They are an extremely important part of the Tasmanian marine ecosystem, providing both food and physical habitat for a wide range of marine species, including important commercial species such as rock lobster and abalone. Kelp forests also improve local water quality and buffer coasts from strong waves.
The fact that neither the community nor Macrocystis has been listed previously at the state or federal level as threatened is particularly concerning, as it means that precious time that could have been used to mitigate some of the threats has been wasted. The prime threats to the kelp forests, noted in the Scientific Committee’s (SC) Advice to the Minister, are a climate-change-driven increase in sea surface temperature, associated with the southward extension of the East Australian Current (EAC), and a corresponding expansion in the range of kelp-grazing sea urchins. Not only is rising sea surface temperature a problem for giant kelp, which is restricted to a range of 5˚ to 10˚C, but the EAC is nutrient-poor compared with the sub-Antarctic waters which it is displacing. Impacts on water quality from land-based activities (such as forestry) and aquaculture are also noted as a threat.
The Advice recognises the long-spined sea urchin, Centrostephanus rodgersii, as the major invasive threat to giant kelp forests. The urchin’s numbers have increased rapidly, to the extent that it has caused serious damage to shallow rocky reefs, mowing down the giant kelp plants that grow there, so that ‘urchin barrens’ now cover significant areas. The urchins are known to remove an entire kelp plant just by eating through the stalk at its base. While warming water is recognised by the SC’s Advice as causing the southward spread of the urchin, it notes that ‘historic’ overfishing of large rock lobsters, Jasus edwardsii, who are the urchin’s only natural predators, has allowed urchin numbers to increase.
In late 2011 the TCT urged the federal environment minister to refuse an export permit for Tasmanian rock lobster, on the basis that the industry is the prime cause of the spread of Centrostephanus, and indeed will ultimately cause a decline in the rock lobster fishery itself as habitat required for recruitment is lost to urchin barrens. 2. The submission was supported by scientific data and reports, and the abalone industry’s submission also specified that the spread of the urchin, due to removal of rock lobsters, is harming the abalone fishery. The point of these submissions is that the rock lobster fishery is a current and continuing cause of the spread of Centrostephanus, not simply a historic threat.
Climate change is a major cause of the decline of the kelp forests, both because Macrocystis can only survive in cold water up to 20˚C, but also because Centrostephanus requires water above 12˚ to breed. Of course, managing climate change is a universal challenge which requires concerted action at many levels to reduce greenhouse gas emissions. However, other threats only make the community’s survival in warming waters more difficult. The ‘Conservation Advice’ approved by the minister recognises that specific actions can be taken, which will be detailed in a recovery plan; however, the only action proposed with regard to the urchins at this stage is research into effective control methods, plus ‘targeted control’. Although scientific research already clearly shows that large rock lobster predation is the only known effective control method, there is no mention of the rock lobster fishery in any of the proposed actions or research.
The SC’s Advice notes that it is difficult to separate the impacts of the various threats involved. If there was an adequate system of marine reserves on Tasmania’s east coast it would be possible for scientists to more precisely determine the causes of decline. As well as protecting species and communities vulnerable to impacts such as overfishing, marine reserves are an excellent way of ensuring that such scientific assessments can be made; by observing the diversity, growth and survival of marine species within the reserve compared to surrounding areas, scientists are able to reach conclusions about the impact of various factors, for example climate change and fishing. Research shows that giant kelp forests are able to survive and thrive in no-take marine reserves such as (part of) Maria Island and Governor Island, which are refuges for large urchin-predating rock lobsters. ‘Considering’ remnants of giant kelp forest for protection in marine reserves is a priority action in the Conservation Advice; however, the forests occur in Tasmanian waters. We can only hope that this listing will give some impetus to the declaration of further marine reserves in eastern Tasmanian waters. After all, as with the giant kelp forests themselves, it has been shown time and again that marine reserves are vital for ensuring recruitment, including of commercially exploited species, to surrounding waters.
Now that the giant kelp forests have, in theory, some hope of protection, it is seriously concerning that the federal government has agreed via COAG to devolve the Commonwealth’s powers over threatened species and communities under the EPBC Act to state governments. Climate change is largely a matter for the federal government and, while it has acted with the ‘carbon price’ legislation, there is much, much more to be done; and it is the Tasmanian gGvernment’s poor management of the rock lobster fishery, and tardiness in establishing adequate no-take marine reserves, that essentially allows the voracious spread of Centrostephanus.
The TCT welcomes this overdue listing. However, with threats such as climate change and an invasive species that thrives in warmer water and whose only predator has been effectively been removed by a fishery, the TCT holds grave fears for the future of this unique and valuable ecological community.
Sharon Moore