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Asterias amurensis and Henderson Lagoon
Invertebrata 21, November 2001

In the July issue (no. 20) of Invertebrata, we reported on finds of the introduced pest, Asterias amurensis (Northern Pacific Seastar), in Henderson Lagoon in Tasmania's Northeast, which marked a significant expansion of its known range in our waters. What made this range expansion particularly interesting from the point of view of pest management was, that for probably the first time anywhere in the world, a significant population of these sea-stars became an entrapped population within an embayment, sealed off from outside waters.

During recent decades Henderson Lagoon has been primarily a tidal estuary, open to the sea at its southern end, but with the occasional closure at the mouth with a massive sand-build following big easterly swells. In early March this year, the lagoon mouth was closed by just such a sand bar, just three weeks after the first specimens of A. amurensis were found by biologists from the Centre for Research on Introduced Marine Pests (CRIMP). At that time I, along with others, made the prediction that with the onset of post-summer rains and the input of freshwater from the many creeks feeding into the lagoon, that the subsequent reduction in salinity of the lagoon waters would result in the demise of all the entrapped A. amurensis. This prediction was based on all the available information on salinity tolerances of this species in the scientific literature: 24 parts per thousand (ppt) was considered its lowest threshold (Marsh 1993, Morrice 1995). However, as reported in our earlier article, the seastar defied our predictions and proved it could survive, and in fact live quite happily, at salinities well below this level.

The closure of Henderson Lagoon to outside waters by natural forces was viewed by many as a blessing and by others as a curse. It was viewed as a blessing by those who saw the entrapment as an opportunity to eradicate the seastar population from the lagoon before it could act as a point source for spread further afield, and also by those who saw it as an opportunity to obtain valuable scientific information on the true environmental tolerances of this pest species.

The negative aspects of the lagoon closure were the impacts to the terrestrial environments surrounding the lagoon, as water levels rose and the lagoon boundary widened. The farmer whose farmland adjoins a large proportion of the western shores of the lagoon reported damage to his pasture from the flooding, loss of stock through drowning and other impacts on his farming activities. Managers/custodians of the Winifred Curtis private botanical reserve at the northern end of the lagoon reported damage to vegetation in flooded areas and were frustrated by being unable to commence a 'Work for the Dole' project in the reserve due to the inundation. A third potential impact and cause for concern was the possibility of flooding of the Tasman Highway near Peat Marsh if the water level in the lagoon continued to rise with winter rains. Suffice to say, there were very vocal and passionate spokespersons in both the 'It's a blessing' and 'It's a curse' camps. As is often the case, Tasmanian Parks and Wildlife staff were caught in the middle and adopted the unenviable role of mediators between those wanting the lagoon to stay closed and those wanting it opened as soon as possible.

Meanwhile, oblivious to all the above-water jostling, down amongst the relative quiet of the sandy/silt bottom of the lagoon, A. amurensis continued to amaze biologists with its resilience to ever-decreasing salinity. On 11 June the first eradication effort was mounted by members of the Falmouth community and surrounding districts, with involvement from CRIMP, Parks and Wildlife, and Marine Resources Division. Although 401 seastars were removed from the lagoon, it was clear to everyone at the end of that day that many more remained. A second eradication effort was organised for 15 July, but nature intervened once more with heavy rains and forced a postponement, as visibility in the lagoon waters fell to near zero.

In the weeks that followed CRIMP scientists, with assistance from several Falmouth residents, made several collections of seastars for laboratory salinity tolerance trials, and for examination of reproductive condition. It was obvious from these collections that the seastars in the lagoon were becoming sexually mature, in synchrony with the normal seasonal pattern observed in populations in southeast Tasmania, i.e. ripening of male and female gonads through June and July in the lead-up to spawning in August/September. The results of laboratory salinity trials, which were supported by in situ field observations, showed A. amurensis could survive at salinities even as low as 12 ppt if changes in salinity were gradual. Some of the seastars collected from the lagoon at these low salinities were found to be actively feeding on bivalves and gastropods, and appeared very healthy.

The second community-based eradication effort was planned for 12 August. During the two days prior to this Sunday, the lagoon was marked out into search zones with ropes and coloured buoys. 'Dummy' seastars (Asterias of similar size to those of the lagoon population, which had been dried, coated in resin, and weighted with lead sinkers) were seeded into the zones to be searched by teams of snorkellers. These dummies were to provide a measure of success of the eradication effort. Twenty-four divers from across the State worked in cold and overcast conditions, hampered by poor underwater visibility, especially in deeper areas of the lagoon. Another 25 people assisted with driving or paddling support boats, ferrying divers to and from the search zones and retrieving catches, and with measuring and recording the seastars and feeding the volunteers.

From the point of view of community involvement, the day was a great success. As with the eradication day in June, the 12 August effort clearly demonstrated the concern people have in our community about marine pest issues and their willingness to do something about controlling them. However, the day was not a resounding success from the point of view of pest control. Divers collected 238 live A. amurensis, but only 19 of a possible 42 dummy seastars were retrieved from six search zones, suggesting that at least another 340 live A. amurensis were still at large in the lagoon. This is a conservative estimate as the placing of the dummy seastars meant that they were more likely to be collected than the real thing. The majority of the seastars appeared healthy, in full spawning condition, and many exuded eggs and sperm while being handled. Bottom salinity in the lagoon was still in the range 11-15 ppt.

Moves to reopen the lagoon mouth to the sea intensified during the two weeks following the second eradication effort, and on the morning of 31 August a bulldozer was employed by the aforementioned farmer to do the job. Needless to say, this action, perceived by many to have occurred with insufficient warning and public consultation, created considerable acrimony, particularly amongst Falmouth residents vehemently opposed to any human interference in the lagoon's natural processes.

A CRIMP biologist surveyed the lagoon the day before the opening (without knowing the lagoon would be opened the next day) and collected four A. amurensis, which all appeared healthy and still happy at around 12 ppt. A CRIMP team surveyed the lagoon again five days after the opening of the mouth, and could find no trace of live A. amurensis. Numerous dead and decaying seastars were found, and many powdery whitish patches on the bottom where the seastars had died and almost completely decayed. It is thought that the seastars were most likely killed by a sudden salinity change - either a sharp increase in salinity with the renewed tidal exchange post-opening, or a sharp decrease in salinity on the lagoon bottom with a breakdown of the stratification that existed pre-opening. It is likely a full tidal exchange regime would have taken a few days to re-establish in the lagoon, so a sudden shift to higher salinity levels is unlikely. Some of our early laboratory trials showed the seastars could survive a sudden transition from 16 ppt into 'full strength' seawater (i.e. 34-36 ppt), so we tend to favor the 'sharp decrease' scenario.

Plankton samples from the lagoon, taken by CRIMP in the lead-up to and at the time of the second eradication effort, and on the day before the opening of the mouth, did not contain any seastar larvae. Trials with larvae spawned and tested in the laboratory suggest that the larval survival rate in the low-salinity lagoon waters would most likely be low. Other trials also suggested the larvae would not survive the dramatic increase in salinity if they were advected out into the sea after opening of the lagoon mouth. However, these trials were not definitive, and can by no means be taken as a guarantee that the opening of the lagoon, while it contained a captive breeding population of a very invasive marine pest, will not result in the appearance of populations of the seastar in the Northeast during the coming summer. Conversely, if the seastar does appear in large numbers this summer in other Northeast embayments such as Georges Bay, there may be no link to the 2001 population in Henderson Lagoon: it may instead be the result of developing patterns of wider dispersal of larvae from populations to the south or even from the north (Port Phillip Bay).

By far the most pleasing aspects of the Henderson Lagoon 'saga' for CRIMP were the very significant contributions of time and effort by numerous community individuals and groups in attempting to rid one of our State's beautiful estuarine habitats of a noxious marine pest, and their genuine interest in introduced marine pest issues. Those people and groups are too numerous to mention here, but on behalf of CRIMP and Tasmania I (CP) thank them again.

As a somewhat depressing aside, during the Asterias saga, CRIMP biologists continued their monitoring of the Carcinus maenas (European green crab) population in Henderson Lagoon. Even when bottom salinity was at its lowest, egg-bearing C. maenas were still being found, and the post-opening survey in early September confirmed many small C. maenas had survived the six months when the lagoon was closed to the sea.

Craig Proctor
Centre for Research on Introduced Marine Pests (CRIMP)
CSIRO Division of Marine Research
Craig.Proctor@marine.csiro.au

Tim McManus
35 Hammond St
Falmouth TAS 7215

Further information on community eradication efforts can be found at www.users.bigpond.com/falmouth

More information:

Marsh, S.E. 1993. The biology and distribution of the introduced seastar Asterias amurensis (Lutken) (Echinodermata: Asteroidea) in Tasmania. Unpublished Honours thesis, University of Tasmania.

Morrice, M.G. 1995. The distribution and ecology of the introduced Northern Pacific Seastar, Asterias amurensis (Lutken), in Tasmania. Final report to the Australian Nature Conservation Agency.

Bede Lowery and those Fire Ants
Invertebrata 21, November 2001

The Red Imported Fire Ant (RIFA), Solenopsis invicta, was detected in Brisbane in early 2001. The discovery made headlines and will continue to do so as eradication of this pest is attempted. All States and the Federal Government will contribute up to $123 million to a five-year eradication project. Certain suburbs of Brisbane will be the focus of this campaign. It is big! Compare this to the $30 million or so expended in the successful Papaya Fruit Fly eradication effort around Cairns in the late 1990s. Quarantine regulations for the interstate movement of pot plants, agricultural equipment and other risky items have been amended through multilateral negotiations that kept Queensland and the unafflicted states reasonably happy in a compromise. So far, the only infestation outside southeast Queensland occurred in Melbourne from potted palms imported from Brisbane. It was quickly eradicated.

The eradication plan has a three-year action phase followed by a two-year monitoring and mopping-up phase. It involves a big public relations program. The current distribution of fire ants in Brisbane, along with information and pictures, can be found at the RIFA website: www.dpi.qld.gov.au/fireants.

Tasmania's Department of Primary Industries, Water & Environment (DPIWE) will look for evidence of RIFA in Tasmania this summer when high temperatures favour detection of RIFA. In the meantime DPIWE is handling more ant identifications than usual as a result of media coverage of RIFA.

What are fire ants?

The Red Imported Fire Ant is native to the Paraguay River catchment in South America. Its native habitat is subject to frequent flooding and drying events, so the species is well suited to open areas disturbed by human activity. Fire ants make subterranean nests of about 150 000 workers (and up to 500 000) that are recognised by mounds (up to 40 cm high) above ground level. Despite having large colonies, fire ants can relocate their nest very quickly.

RIFA defend their nests aggressively against any perceived threat. Ants will rush from the nest, climb all over their attacker, and - on the release of an alarm pheromone - sting in synchrony. The sting of fire ants is particularly painful. They can sting repeatedly and will continue to sting even after their venom glands are empty. Their large nests, aggressive nature and painful stings make the fire ant a frightening pest in urban and agricultural areas. Some people have fatal allergic reactions to proteins in RIFA venom. The proportion of allergic people is much greater than for honeybee stings.

Two types of RIFA are known overseas: one type has single queens in each nest, the other has multiple queens. An ant species that has colonies with multiple queens is called polygynous. Nests with multiple queens are more problematical because new nests established by a polygynous colony are not aggressive to each other or to the parent colony. The result can be a nest-system that extends over hundreds of metres - similar to the huge nest systems of Argentine Ant.

Economic impacts

Fire ants have kept many entomologists employed in the USA, as can be seen from article titles in the Journal of Economic Entomology through the 1980s and 1990s. It is virtually a research industry!

Fire ants are a major pest of economic and social importance. Dollar values can be placed on costs such as household repair and control, substantial decrease in property value of infested land, agricultural losses through injury or loss of baby livestock (fire ants can blind calves), impediment of machinery by nest mounds, infesting of stock feed, medical treatment of humans and their pets, time off work due to stings, and damage to schools and school property. These costs are substantial and by themselves justify the eradication attempts.

The social impact of fire ant is also important. As Australians, how much do we value our outdoor lifestyle? Fire ants restrict leisure-time in our backyards, make gardening a painful pastime, prevent children from playing in infested areas and make walking around in bare feet or thongs dangerous. Fire ants wreck BBQs!

Identifying the fire ant

RIFA are 2-6 mm long and brown, with a hefty sting. Apart from these characters, little more can be said of fire ant identification with the naked eye - or skin! After this, microscopic identification is necessary.

RIFA belong to the large subfamily Myrmicinae in the family Formicidae. In Tasmania, this subfamily is easily recognised by being small ants (usually < 1 cm long) with two nodes (swellings) on the petiole (waist) and small mandibles (jaws). The only other ants in Tasmania with two petiolar nodes are the Myrmeciinae, which include the notorious inchmen and jack-jumpers, all of which are much larger than RIFA and have prominent, long jaws. The Myrmicinae are represented by about 20 native species in Tasmania, including one species of Solenopsis. How do we know the difference between Solenopsis invicta and other native species? Enter the Bede Lowery collection - the best synoptic collection of Tasmanian ants in the State.

The Bede Lowery collection

Reverend Bede Lowery worked for the Roman Catholic Church in many parts of Australia. He worked at Latrobe and Devonport for several years up to his death in 1996 at age 72. Bob Taylor, a retired CSIRO entomologist, described Bede's work in the Australian National Insect Collection newsletter (ANIC News 7:4-6, October 1995, and 11:12, October 1997. Bede greatly extended the checklist of Tasmanian ants during his residence in the State. He deposited three synoptic collections of ants in Tasmania, one each in the State Museums (QVMAG and TMAG) and one at Forestry Tasmania. During August, the authors visited Craig Reid at QVMAG to get our heads around the Tasmanian Myrmicinae.

The Bede Lowery collection allowed us to see, in one place and at one time, all the ants of Tasmania. We quickly identified the ants most similar to Solenopsis invicta. The native species Solenopsis froggatti was readily discounted. It is minute (about 1 mm long) - much smaller than RIFA. More similar are species of the related genus Monomorium. They are about the same size as RIFA but can be separated on the basis of their antennae. Species of Monomorium have 11- or 12-segmented antennae, and the last three segments are swollen to form a small club. Species of Solenopsis have 10-segmented antennae, and only the last two segments are swollen to form a small club.

Bede's synoptic collection also proved useful when we received a quarantine alert for Little Fire Ant, Wasmannia auropunctata, which recently invaded Hawaii. This ant is like a tiny Solenopsis, much like the native S. froggatti. How do we distinguish this ant from native Tasmanian ants? Easy - our notes on Bede's collection reveal that S. froggatti bears no spines on its propodeum, but Little Fire Ant has a pair of large spines.

The Bede Lowery collection will continue to be useful for years to come. Using it, entomologists like ourselves can examine specimens for characters mentioned in books and thus develop our ant-identifying expertise more rapidly. Using the collection, we can now identify all ants to genus with ease, and with more time we could use Bede's collection to make species-level keys for any desired group of Tasmanian ants.

Owen Seeman
Entomologist, DPIWE
St Johns Terrace
New Town TAS 7008
ph (03) 6233 6827
Owen.Seeman@dpiwe.tas.gov.au

Lionel Hill
Entomologist, DPIWE
P.O. Box 303
Devonport TAS 7310
ph (03) 6421 7636
Lionel.Hill@dpiwe.tas.gov.au

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