The long spined urchin has undergone range extension southwards from its native habitat in New South Wales waters over the past 40 years. It has been able to thrive in Tasmanian waters more recently due to the warming waters off the East Coast largely associated with changes to the East Australian Current.
Why is it a problem?
Fisheries that rely on healthy rocky reef habitat are very important to the Tasmanian community from an economic and social perspective. The community has an expectation of pristine, balanced reef systems however, once established on a reef, the long spined urchins graze on kelp and other marine plants, forming bare patches called 'incipient' or emerging barrens. If left to its own devices, urchin numbers will continue to increase and the level of overgrazing on kelp is likely to completely denude the reef of all seaweed, forming an 'extensive' or established barren.
These extensive barrens significantly impact on the biodiversity of rocky reef habitat with devastating impact on recreational and commercial fisheries particularly abalone, rock lobster and some scalefish species robbing these fisheries of feed and habitat. Once established, the extensive barrens can be maintained and can continue to expand by just a few urchins. The point where incipient (patchy) barrens become extensive (bare bottom) barrens is referred to the tipping point which is pivotal to the management approach adopted. The full-blown extensive barren, requires the removal of all the urchins from the site to be cleared over an extended period before we can turn back the clock and allow the algal habitat and fisheries to recover.
Large rock lobsters are one of the few natural predators of the long spined urchin. However, lobster stocks have declined on the East Coast due to periods of low recruitment and fishing activity.
A combination of climate change and depleted lobster stocks are important factors contributing to the expansion of long spined urchin barrens.
What is known about urchin barrens?
A recent report by the Institute of Marine and Antarctic Studies (IMAS) on long spine sea urchins on reefs along Tasmania's East Coast (the
IMAS long term study) has measured increases in the urchin population and the barren areas they create by overgrazing kelp beds.
Urchin barrens can extend over hectares of the seabed and in depths up to 60 plus metres. But peak barren formation occurs in a depth range of 20 - 30m.
There are some baseline data of the abundance and distribution of long
spined sea urchin barrens resulting from the, systematic surveys conducted by
IMAS in 2001/02 which were re-surveyed in 2008/09 and then again in 2016/2017 by
IMAS divers and underwater towed video to monitor changes and trends in the
abundance and extent of the impact of the long spined urchins over time.
Is the problem getting worse?
The latest IMAS survey estimates that the biomass of long spined urchins in 0 - 18m depth is around 3,276 tonnes with major barren formations in the vicinity of St Helens, Freycinet, Schouten Island and Maria Island.
Smaller barrens are currently forming in the Eddystone Point, Four Mile Creek, Bicheno and the Tasman Peninsula regions.
Data from a towed video survey in 18 - 30m depth range suggest a similar biomass level to inshore or a total long spined urchin biomass of around 6500 tonnes.
What management action is being taken?
eradication of the long spined urchin is not considered possible, a lack of active
intervention is predicted to result in a
steady increase in urchin barrens. The latest IMAS report does suggest possible
actions and it is encouraging to note that continued proactive management of
urchin overgrazing, such as rebuilding urchin predators and upscaling of
culling and/ or harvesting activities appear to be plausible means of control’.
One of the key components
in the battle against the northern invader is the recent allocation of $5.1 M
over 5 years allocated by the Tasmanian State Government to support and increase the sustainability and productivity of the
Tasmanian abalone fishery.
The funds are administered by the Abalone Industry Reinvestment Fund Committee (AIRF)
, which operates on a co-management approach between the abalone industry, the Department and IMAS. It is a significant acknowledgement of the threat posed by the urchins that all industry, Government and research members on the Committee have prioritised Centrostephanus as a key threat to abalone with in excess of 50% of the funding being allocated to address the incursion.
The additional funding has allowed a multi-pronged approach to be put in place to tackle the long spined sea urchin with a range of future options also being considered. Current and past research data is available to underpin any future management actions that will be undertaken and this information base is expanding rapidly.
One of the key developments the AIRF has progressed, is the development of an overarching State strategy to guide the control efforts for the long spined urchin to help ensure that consistent aims and objectives are maintained. The State strategy is spear-headed by Dr David Westcott, a renowned world expert in such plans having already prepared the strategy to tackle the crown of thorns sea star threat to the Great Barrier Reef.
Main Objectives of the StrategyReducing the ongoing risk of the destruction of healthy kelp beds and then rehabilitating established urchin barrens to a balanced habitat are fundamentally two different problems requiring different solutions.
The multi pronged sea urchin strategy has three key objectives:
- Stop growth of existing barrens
- Prevent establishment of new barrens
- Promote recovery of full barrens
Strategies to achieve the objectives
The severity of the threat posed by long spined sea urchins to Tasmania's rocky reef ecosystems and consequently to the fisheries, tourism operations and local communities who depend on the natural balance being maintained requires the urchin to be tackled with an array of weapons.
Possible means include:
- a biological approach such as the re-building and translocation of rock lobster stocks;
- market based strategies such as subsidies and the development of new domestic and overseas markets; and
- a physical approach which includes divers smashing and harvesting the pest.
All these strategies are currently being employed and are having an impact. There are also a number of research projects which are showing promise for future control options.
Liming is a real possibility following its successful use in controlling sea urchins overseas. These overseas cases have shown builders lime has a devastating affect on the urchins when only a few grains are applied to the test (shell inside the spines). However there will need to be extensive testing under local conditions before any Tasmanian ecosystems are exposed to the treatment.
The urchins are also being assessed for their effectiveness as a
fertiliser through a collaborative approach between industry and IMAS while a
project to evaluate the most efficient use of subsidies has just been completed. These varied applications all make taking the
urchins a more attractive proposition for divers and processors alike.
Below is a brief description of some of the more prominent tools currently being used to control the incursion.
On extensive barrens, kelp will only be restored by ‘direct human intervention’ such as culling. Predators such as large lobsters are unlikely to reduce urchin numbers to the point where the seaweed can re-establish itself. In other areas including incipient (patchy) barrens, commercial harvesting can be an important tool.
It was initially thought there were no markets for long spined sea urchin roe as the roe was considered bitter and unpalatable. Market interest in the product has now increased following development of better processing techniques which has , in turn, resulted in very successful market development.
The tonnage of longspined urchins harvested had been gradually increasing from 2008 to 2014 when the harvest reached 97 tonnes. Interest waned in 2015 and 2016 as processing facilities showed little interest in progressing the development of the longspined fishery. However, in 2016, the abalone industry introduced a subsidy to be paid to the commercial dive sector as a means of enticing fish processors into harvesting the urchins for the roe.
The subsidy was a resounding success, with one processor in particular investing heavily in the product and being rewarded by the expansion of demand for the product exceeding expectations.
The subsidy is now funded by the AIRF and over the last year over 555 tonnes of urchins have been removed from Tasmanian State waters primarily for the sale of their roe (gonads). That equates to roughly 1,665,000 longspined urchins which will now no longer destroy valuable abalone, rock lobster and scalefish habitat. A graph of the development of the Centrostephanus harvest is shown below and the impact of the subsidy in 2017, 2018 and 2019 can be clearly identified. It should be noted that the IMAS surveys indicate that the longspined urchin biomass off Tasmania, has been increasing by some 180 tonnes annually. Over the last 12 months, the commercial fishery has e removed three years of expansion by the urchin.
Tonnage of long spined sea urchins taken by commercial divers by fishing year
All reports suggest that the areas that were harvested are already showing significant signs of improvement but a project funded by the AIRF will soon be undertaken to quantify the effects of commercial fishing on the Centrostephanus numbers and the recovery of barrens.
Ongoing commercial harvesting is likely to be an important ongoing activity to reduce urchin numbers. The need for a continued subsidy is an issue that will require further consideration and is being assessed by a subsidy evaluation project funded by the AIRF.
Read more about Tasmania's commercial sea urchin fishery
Centrostephanus roe as the final product
Centrostephanus being processed to extract the roe
East Coast Stock Rebuilding Strategy
The East Coast Stock Rebuilding Strategy commenced in 2013 and aims to rebuild lobster stocks from less than 10% in some areas to greater than 20% of an unfished or virgin fishery by 2023, by limiting the total catch (commercial and recreational) each year from an area between Eddystone Point and Bruny Island.
More information about the
East Coast Stock Rebuilding Strategy
What role can large lobsters play?Large lobsters at sufficient density are able to limit urchin populations effectively in healthy kelp beds to help minimize risk of barrens formation. Large lobsters are also able to limit urchin populations on incipient barrens, facilitating recovery of seaweeds and minimizing risk of further expansion of barrens.
While large lobsters do prey on urchins, increasing rock lobster
biomass alone will not result in the recovery of extensive urchin barrens. on
extensive barrens which has been shown to significantly reduce urchin
densities, they are unable to reduce urchin numbers to the point where kelp and
other seaweed can re-establish. Even if extensive barrens are closed to
lobster fishing indefinitely and populations of large lobsters on barrens are
boosted by transplanting at realistically achievable levels, the likelihood of
recovery of kelp is negligible in the absence of any other mechanism to reduce
urchin density. On extensive barrens, kelp will only be restored by additional
intervention, for example by removing urchins using divers, quicklime, or
Once urchins are at sufficiently low densities to allow reef habitat to recover, maintaining populations of large lobsters in regenerated kelp beds is likely to be sufficient to prevent return to urchin barrens.
Rock Lobster Translocation Program
The stock rebuilding strategy is also supported by the East Coast Translocation Program. Under this program, undersize lobsters from slow-growing deep-water areas in the South West are translocated to inshore east coast locations including known incipient barren areas.
Read more about the
Rock Lobster Translocation Program
Culling by smashingCommercial divers and abalone divers have culled long spined urchins as part of research projects over the last 10 years. This is
another ‘direct human intervention’ tool that can help protect small specific
patches of reef from turning into extensive barrens.
Culling of long spined urchins can be undertaken by commercial divers
In terms of other forms of physical intervention, trials have shown that urchins can be culled from discrete areas and that regrowth of kelp may occur in that area. These removals are more successful if at least two episodes of removal are conducted – and may require further ongoing efforts for long term removal.
However, such programs would seem practical in only small or key areas due to the resource intensive effort required. Other forms of voluntary action may also have some impact.
The utility of developing a management framework for recreational dive groups to undertake similar ‘protect a patch’ activities may be considered in the future.
To assess the effectiveness of current and novel mitigation methods, future surveys of urchin density and barren coverage would be required. The effectiveness of fishing/ mitigation measures may also benefit from fine-scale spatial mapping of effort via GPS and depth loggers and/ or mobile web-applications.