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Bad news from Henderson Lagoon
Invertebrata 20, July 2001

Henderson Lagoon is an irregularly shaped tidal estuary, shallow and about three kilometres long, which normally opens into the sea just north of Falmouth on Tasmania's East Coast. Occasionally the barway becomes sanded over, impeding the outflow of several creeks which feed the Lagoon, and flooding adjacent farmland.

During the latter half of the 1990s, Henderson Lagoon became the focus of attention of scientists from CSIRO's Marine Research Division. The reason was the introduced European Green Crab, Carcinus maenas, which for unknown reasons seemed to be thriving in the Lagoon. However, subsequent field surveys revealed a waxing and waning of Green Crab numbers, adults sometimes disappearing altogether. Researchers realised that to understand what was happening to the population as a whole, younger (post-larval) C. maenas would have to be studied.

In addition to standard crab traps for adults, passive benthic collectors were deployed to provide a haven for newly settled juveniles. The collectors were short lengths of PVC pipe, 16 cm in diameter. Each was filled with 'Hogshair', a synthetic fibrous material used in air-conditioner filters, and the collector ends were covered with 6 mm oyster mesh. Suitably weighted, the collectors were placed on the sea bottom at selected sites.

On 14 February this year, scientists were surprised to find a tiny introduced North Pacific Seastar, Asterias amurensis, arm radius 1.0 cm, inside a larval trap placed in mid-January in the deepest part of the channel east of the Roses Creek mouth. The following day a 2 cm A. amurensis was found in one of the adult crab traps. (These traps are set once a month, overnight, during summer and autumn.) On 14 March a 2.6 cm A. amurensis was found under one of the passive collectors, and the next day a 2.5 cm A. amurensis was seen on the bottom in the channel, again east of the Roses Creek mouth.

The unfortunate discovery of free-living A. amurensis in the Lagoon raises several questions, not least of which is 'How did it get there?' The offshore coastal current on Tasmania's East Coast is from north to south, which would seem to mitigate against spread of A. amurensis from infestations near Hobart. Nevertheless, when this pest was first identified in the Derwent over a decade ago, the distinguished marine biologist Isobel Bennett warned one of the authors (TJM) that eventually, one way or another, the wretched starfish would spread to every estuary in Tasmania!

The A. amurensis population in Henderson Lagoon is presently small. Further south, though, there have been recent reports of 'very large numbers' of North Pacific Seastars in scallop spat collector bags and suspended 'grow-out' cages near Triabunna. Has the pest spread north to Henderson Lagoon in contaminated recreational fishing gear? Whatever the route, the introduction probably occurred towards the end of the 1990s. Native oysters, Ostreas angasi, as well as escapees from commercial oyster beds in Georges Bay are sufficiently plentiful in Henderson Lagoon to serve as a ready food source for the adaptable exotic predator.

What will happen if A. amurensis spreads to Georges Bay? In time it could decimate the local oyster industry. Assuming there are no discoveries of A. amurensis north of Henderson Lagoon, should some sort of quarantine be placed on the Lagoon to reduce the possibility of spreading? An information campaign to encourage public assistance, both to remove North Pacific Seastars from the Lagoon and to end recreational fishing there, might be a sensible initiative.

Meanwhile, Nature has already imposed a barrier which could prevent movement of A. amurensis in or out of the Lagoon, and could even result in its complete eradication there without any human assistance. On 9 March the mouth of the Lagoon was closed by a massive sand bar, pushed up by a large northeasterly swell in combination with a big spring tide. A similar closure in February 1999 quickly resulted in the Lagoon becoming a brackish lake; the Lagoon was later re-opened with a bulldozer.

Although a sand barrier could be advantageous from the point of view of pest management, it does have its down-side. Prior to the latest closure, a very low spring and summer rainfall total had led to the development of a stable marine community in Henderson Lagoon. Thick seagrass meadows appeared in parts of the Lagoon where they had not been seen before, fish life increased in abundance and previously unseen invertebrates (native seastars, urchins and octopi) were becoming common.

At the time of writing (4 April) the Lagoon is still closed and is likely to remain so for at least a few more weeks. Since closure, the heaviest one-month rainfall since January 2000 (90 mm) has been recorded. The marine ecosystem in the Lagoon is dying, but hopefully so are all the North Pacific Seastars.

Once upon a time, the sea around Falmouth was seen as the pristine standard against which other Tasmanian estuaries could be compared. Then the Rosy Screw Shell, Maoricolpus roseus, appeared in abundance. Next came the European Green Crab, and now the third in a trio of alien marine scourges, A. amurensis, has established a 'tube-foothold', albeit a tenuous one. Hopefully that's the last of the bad news from Henderson Lagoon!

Stop press!

Our original article (above) suggested, optimistically, that a natural decline in salinity from rainfall might eliminate the unexpected infestation of A. amurensis in enclosed Henderson Lagoon. Indeed, current literature infers that 24 ppt is the minimum level of salinity North Pacific Seastars require to survive. Now, on 17 June, we know we were wrong!

Despite the Lagoon remaining closed to the sea since early March, on 28 May a local professional diver was able to collect, without difficulty, half a bucket of adult Asterias. Subsequent salinity measurements around the Lagoon revealed the alien starfish appeared to be thriving in brackish water with salinity levels ranging from 16-20 ppt, and there was no evidence of salinity stratification with depth.

Division of the Tasmanian Department of Primary Industry, Water and Environment (DPIWE) to devise an action plan. The local rainfall since 9 March had been 190 mm and the Lagoon was very full. It was feared that if the barway was breached, significant numbers of adult Asterias, approaching their reproductive period, would be distributed up and down the coast.

A combined operation was mounted to both outline the extent of the infestation and to physically remove as many North Pacific Seastars as possible from Henderson Lagoon. The operation was conducted on the Monday of the June long weekend and involved members of the community from Falmouth and environs. The day before, 21 baited traps had been set over a wide area in an attempt to define, and encourage, sites of greater starfish concentration. The baiting was a failure: only three Asterias were found in the traps on the Monday.

The joint scientist/community starfish collection effort was much more successful. In just three hours, 391 A. amurensis were captured and measured by six snorkellers and 20 people in an assortment of motorised and paddle craft. All specimens were retained for later examination. Snorkelling seemed to be the most effective method, although rather uncomfortable with the average water temperature at only 9.5ºC, but it was clear that many more Asterias had been missed because they were hidden in the seagrass.

It is not going to be easy, and it may not be possible, to eradicate A. amurensis from Henderson Lagoon. Visual observations indicate there are plenty left, but seven traps deployed during the week after the joint exercise caught only one starfish. It may be that there is too much natural food in the Lagoon for the starfish to be attracted to bait. See the next Invertebrata for further developments!

Tim McManus
35 Hammond Street
Falmouth TAS 7215

Craig Proctor
Centre for Research on Introduced Marine Pests (CRIMP)
CSIRO Division of Marine Research
ph 62325376
craig.proctor@marine.csiro.au

Beetles for bones
Invertebrata 20, July 2001

The QVM Zoology Department has over the years developed an extensive reference collection of vertebrate skeletal material. Cleaning these skeletons can be a very messy, time-consuming and often fiddly process, unless the 'zoology assistants' happen to be Dermestes maculatus (Coleoptera :Dermestidae).

For over 20 years, these nondescript little black beetles and their voracious larvae have been harnessed to clean all manner of vertebrate carcasses, from bats, small birds and snakes through to bits of whales. Dermestes require dried material to feed on and this is facilitated by removing the major muscle masses and organs from specimens before air-drying.

Beetle colonies are kept in 600 x 600 x 1200 mm stainless steel tanks, each closed with a close-fitting perspex lid. The bottom of each tank is covered by a layer of raw wool 80 -100 mm thick in which the beetles pupate. (When the tanks were cleaned two years ago, the bedding in each started out as three fresh sheep-skins from the local meatworks!)

Since the beetles prefer to work in low light conditions, the tank lids were covered with black plastic leaving only meshed ventilation holes. The adult beetles are ungainly fliers but they reach the ventilation mesh occasionally, necessitating three or four sharp raps on the lid to dislodge them before the tanks are opened.

The 'Beetle Room' is bare except for essential gear, and is painted white so that would-be escapees have nowhere to hide. Clinical the decor may be, but it also makes it easier to control the Cupboard Spider (Steatoda livens) which can be a predator of Dermestes.

Over five or six weeks, the larvae feed voraciously and grow to hairy behemoths of 15 mm in length before they pupate. We sometimes segregate the smaller, more delicate vertebrate specimens with a limited number of early instar larvae. Later instars en masse can quickly disarticulate a skeleton completely and scatter the bones, making them difficult to find amongst the frass and exuviae. Colony activity is maintained year-round by keeping the 'Beetle Room' at a constant 24ºC. Beyond this, the only control on beetle populations is food: the more they're fed, the more beetles there are. When specimens are few, a 'skeleton staff' can be easily maintained with dried lamb scraps or butcher's bones.

Craig Reid
Queen Victoria Museum and Art Gallery
Wellington Street
Launceston TAS 7250
craig@qvmag.tased.edu.au

News from QVMAG
Invertebrata 20, July 2001

Things are happening at the Queen Victoria Museum - at the moment it is mainly talking and 'moving deck-chairs', but it's all very promising. I took over as Acting Curator of Zoology in April, working three days a week and Bob Mesibov joined the staff just over a month later working two days a week. Bob's position is Curatorial Specialist and his main task initially is to undertake an audit of the earthworm collection, about which there has been some recent contention. Lisa Joy Boutin is also part of the team, being employed on outside funding to continue her spider work (though she is currently collecting in Northern Territory, having returned not too long ago from New Caledonia and Madagascar!). So Zoology at the QVM now consists of six part-time staff - the three mentioned above plus Tammy Gordon, Judy Rainbird and Craig Reid. Our area of responsibility has also increased to include a collection management role for the Botany holdings, though we are not fielding botany inquiries.

We have done some reorganising of office and laboratory space and are now moving forward on several fronts. Work should be starting in the next couple of months on the first stage of our new Zoology wet store, to provide better housing for material preserved in alcohol. The store is being built on the Wellington Street site, the first stage should be completed this calendar year and this will allow us to bring the vertebrate collections back from the temporary store at Rocherlea. Rehousing and a curatorial up-date of this collection will be carried out prior to its move to the new store. The new dehumidifier in our main Zoology store in the TAFE College is working well to counter the effects of the cold, damp Launceston winter.

This general increase in 'house-keeping' activity is spilling over into other areas of collection management. Working sessions with our system manager Mark Gordon have commenced, aimed at bringing our nine zoological collection databases ultimately down to two: vertebrate and invertebrate. This will make for much more effective database management and will greatly increase the quality of our collection data.

All this activity on 'collections' has still allowed some time for progress in the other two areas of responsibility, namely research and public programmes. Lisa, Bob and Brian are continuing work on spiders, millipedes and snails, respectively, with Brian also preparing another issue of Molluscan Research for publication. Public inquiries have slackened off a bit over winter but still occupy significant time for Judy, Tammy and Craig. These three have also been involved with the new 'Discovery Plus' activity area which has been moved to a larger gallery. 'Discovery Plus' contains quite a bit of zoological material and is proving very popular with school groups and families - thanks to the work of Alisanne Ramsden and her team. Although the major focus of QVM staff will be the opening of the Inveresk Railyards complex later this year, natural history in the Wellington Street building hasn't been forgotten, and our work rate has increased!

Brian J. Smith
Acting Curator of Zoology
Queen Victoria Museum and Art Gallery
Wellington Street
Launceston TAS 7250
ph 63233777
brian@qvmag.tased.edu.au

Recent spider crab aggregations
Invertebrata 20, July 2001

Since July 1999, when an article on spider crabs was published by Caleb Gardner in Invertebrata, there have been many reports of aggregations and sometimes strandings of the crab Leptomithrax gaimardii (M-Ed.) around Tasmania. Each late autumn to winter the crabs have been arriving in seemingly predictable locations to mate and to moult. Repeated sightings have been made along the northwest coast, at Dunalley, all through the River Derwent Estuary and the D'Entrecasteaux Channel. Other reports have come from Swansea and the Freycinet. The species is also found all around the southern Australian coastline. In the River Derwent they frequently aggregate off the suburban shores of Hobart, and right up into the city at Watermans Dock, a stone's (crab's?) throw from Parliament House! In autumn 2001, the Royal Yacht Club of Tasmania in Sandy Bay, Hobart, had to call in divers to remove ten-deep crabs from the rails of their slips before a boat could traverse them.

The crabs are large and may have a carapace span of 120 mm. They occur seasonally from shallow water to over 800 m in depth, and are white and orange in colour. The males have larger front claws than the females. The carapace is very hard and prickly and the best way to pick them up, if you must, is from the rear, though a well-endowed male can still reach your fingers (personal experience).

The crabs graze on algae and prefer shallow, silty areas to moult and mate, and will form dense aggregations at these times. These events are quite common as Leptomitrax gaimardii is an abundant species around Tasmania's inshore coast. Aggregations, sometimes a metre high and many metres wide, are a natural process and may occur for several reasons.

When the females are soft-shelled after moulting they become sexually receptive to mating. This may attract males in large numbers. Sometimes mounds of crabs may all be moulting at the same time, and this may be a protection against predators. When a large aggregation of crabs occurs offshore, and the weather is blowing onshore, masses of crabs may be washed up on beaches and these events are called strandings. A close inspection may show that many of the 'crabs' are the empty cast-off shells. Between moults the carapace and often the legs as well can be covered with tube worm casts and algae. It must be a great relief for the crab to shed its tight shell and move about freely again.

The earliest account of Leptomithrax gaimardii in Tasmania was from Francois Péron's accounts of his journey around Tasmania in 1802, where he described aggregations as 'spider crabs, which delight in filth and mud, abounded to excess on every point in the [D'Entrecasteaux] Channel' (Plomley et al. 1990). The Channel is still one of the most often reported areas for aggregations.

Although the crabs are reported to be good eating, there are regulations about taking living marine animals from the sea without a permit.

Liz Turner
Curator of Invertebrate Zoology
Tasmanian Museum and art Gallery
GPO Box 1164M
Hobart TAS 7001
lturner@tmag.tas,gov.au

Further information:

Gardner, C. 1999. Spider crab aggregation on Tasmania's northwest coast. Invertebrata 14.

Hale, H.M. 1927-29. The Crustaceans of South Australia. Adelaide: Government Printer, South Australia.

Plomley, B., Cornell, C. and Banks, M. 1990. Francois Péron's natural history of Maria Island, Tasmania. Records of the Queen Victoria Museum 99.

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