Hello
Thanks for the question - it's a subject that interests me, so I've
dug up a lot of info for you. There's a lot more at the CSIRO lim=nk
at the bottom of the answer.
General info on the lifecycle and biology of the "Japanese starfish"
____________________________________________________________________
Asterias amurensis, commonly referred to as the northern Pacific
sea-star, is native to the coasts of northern China, Korea, Russia and
Japan. However, the distribution of this sea-star has now increased,
following its infiltration into a number of other countries, including
Australia ,and Tasmania in particular.
The sea-star was first found in Tasmania in 1986, but at the time was
mis-identified as a native species. It was not until 1992 that the
sea-star was identified as A. amurensis, a species which is not native
to Australian waters.
Based on the distribution of northern Pacific sea-star populations in
shipping ports and their intolerance to warm water, the most likely
mechanism of introduction into Tasmania was the transport of larvae in
ballast water, which was then jettisoned into the sea.
The shipping industry within Australia, along with overseas vessels,
have the potential to spread the seastar to the rest of Australia, and
it has already been found in Victoria.
Other mechanisms have been recognised as facilitating the spread of
the sea-star to other parts of the world, including the movement of
commercial bivalve shellfish for aquaculture.
Here’s a description of the species from "Introduced Marine Aquatic
Invaders: Northern Pacific Sea-star
(http://www.fish.wa.gov.au/hab/broc/marineinvader/marine01.html )
"The sea-star is a large voracious predator, reaching sizes 40 to 50
cm in diameter. In its native range, the sea-star prefers water
temperatures between 7 and 10o C, but has adapted to warmer waters (up
to 22o C) in Australia and other countries.
"In one year the sea-star is capable of increasing its diameter by 8
cm. It is capable of reproducing at 10 cm. In Australia spawning
occurs during winter (July to October) at temperatures of 10 to 12o C
when females may carry up to 20 million eggs per adult. Fertilisation
is external and fertilised eggs develop into free swimming larvae that
remain in the plankton for around 90 days, before settling and
metamorphosing into juvenile seastars.
"Larval survival is constrained by temperature and salinity, with the
optimal ranges being respectively 8 to 16 o C and 3 to 8.75‰ .
Generally, the seastar is sensitive to salinity changes and is
therefore unlikely to be found in areas with fluctuating salinities.
"The seastar lives for up to five years and in Japan its numbers
increase and reach outbreak proportions lasting two to three years.
These outbreaks tend to occur in three or ten year cycles and there
have been some suggestions that the outbreaks are a symptom of a
degraded environment.
There’s also a picture of the sea-star at the above site.
The northern Pacific seastar is commonly found near to the shore, but
also occurs in water depths down to 200 m. It is rarely found on reefs
or in areas with high wave action, instead happily settling on either
mud, sand or pebble substrates. In Tasmania, juveniles and adults have
also been found attached to scallop longlines, spat bags, mussel and
oyster lines, and salmon cages.
The animal is a voracious predator and will eat almost any animal
tissue it can capture. However, the sea-star has a particular fondness
for shellfish, whose flesh it eats after prising their shells open
with its arms. This preference for shellfish poses a serious threat to
mariculture and wild shellfish fisheries. The sea-star is also capable
of detecting food from some distance away and will dig shallow pits to
extract buried prey.
Up to 30 million northern Pacific sea-stars are currently present in
the Derwent estuary in Tasmania and are considered a major threat to
the Abalone industry.
There’s a nice summary of the animal and it’s life-cycle at "CSIRO
Marine Research: The Northern Pacific Sea Star" here:
http://www.marine.csiro.au/LeafletsFolder/npseastar.html
Effects of the starfish in Tasmania
___________________________________
There have been numerous scientific studies done. ( You'll find a lot
more at the CSIRO site link at the bottom of the answer ) All the
studies have shown the starfish to be a voracious predator of
"abalone".
In a study "Impact of introduced seastars Asterias amurensis on
survivorship of juvenile commercial bivalves Fulvia tenuicostata " the
authors concluded that :
"….In a manipulative experiment, densities of F. tenuicostata
juveniles (..a type of abalone…) were reduced by around 15 fold (from
580 to 35 m-2) in the presence of sea-stars at background densities
relative to the treatment without sea-stars…."
"…..predation by A. amurensis is largely responsible for the recent
decline and subsequent rarity of large bivalves in its current
distribution in Tasmania. The potential of seastar predation to have
wider ecosystem level effects than the short-term direct effects
reported here is a major concern. "
You can see the full summary, and a link to the full report here:
( http://www.int-res.com/abstracts/meps/v241/p99-112.html )
So the sea-star feeds voraciously and omnivorously on shellfish, and
virtually all sizeable bivalves and other attached or sedentary
invertebrates are eliminated where seastar densities are high. This
may not only affect the biodiversity, but also have effects on the
ecosystems of which bivalve filter-feeders are a key component.
The seastar threatens the fisheries of southern Australia - even in
its native range it has a significant impact on fish and shellfish
productivity. It has wide temperature and salinity tolerances, and
populations in the Derwent estuary have grown to the point where it is
the dominant invertebrate predator of some benthic communities.
Population densities easily exceed those recorded in its native range
- one estimate puts the Derwent Estuary population at 30 million. Its
impact is considered so significant that ports in Tasmania, and now
Port Phillip Bay, are the only ports in the world from which ships are
prevented from releasing ballast water in New Zealand's coastal waters
under any conditions.
Control
______
Various efforts are being made to control the sea star population
Again, from the CSIRO site above:
"The Tasmanian Government has set up the National Seastar Task Force
to coordinate research on the seastar. An identification poster,
produced jointly by the Task Force, the Tasmanian Museum and CSIRO,
was distributed widely in coastal areas of southern Australia to
encourage the community to report sightings of the seastar, assisting
scientists to monitor its spread.
"Studies of the biology and impacts of the seastar were funded by the
Australian National Conservation Agency and carried out by the
Tasmanian Museum and the University of Tasmania. The Department of
Primary Industries and Fisheries carried out trials with a
Tasmanian-designed trap that has the potential to control seastar
numbers around marine farms.
"CSIRO scientists have established valuable links with Japanese and
Russian scientists who have been studying the seastar in its native
habitat. This has led to the identification of several parasites that
warrant further investigation as potential biological control agents.
Work is underway to assess the specificity of the hosts of the most
promising of these parasites
An article at CABI: Biocontrol News and Information nicely summarises
the various control attempts being made.
( http://pest.cabweb.org/Journals/BNI/Bni20-1/gennews.htm )
"Physical removal of seastars using divers or traps has been trialled.
Community divers removed 30,000 seastars from around the Hobart
wharves on two occasions in 1993, or perhaps 60% of the animals from
an area that is a fraction of the occupied area. Traps provide a more
cost-effective alternative to control chronic infestations, but at low
densities attract seastars in from outside the area. Dredges and
trawls have been used in Japan to control the seastar prior to seeding
an area for shellfish aquaculture, but associated environmental damage
would be excessive in an unfished area. Non-specific chemicals,
principally quicklime, have been used to locally control seastars on
shellfish beds, but collateral damage is high.
"Non-specific physical and chemical control may have a role in local
control of seastars around aquaculture farms, but Bax points out that
control of the seastar population will require a highly specific
control agent that can be widely dispersed throughout the population.
Specific predators have not been found, although one larger native
seastar does eat Asterias in laboratory situations.
"Potential parasites for biocontrol have been sought in Japan and
Russia, in collaboration with the US team led by Kuris and Lafferty.
From hundreds of seastars sampled during the first survey in Japan, a
single specimen, from the far-eastern arm of Hokkaido was found to be
infected with a ciliate parasite. A second survey during the peak
reproductive season found the ciliate to be abundant and widespread.
So far this species, the scuticociliate Orchitophrya stellarum, is the
only one to show promise. It partially castrates Asterias in its
native range, and is associated with mortalities of another seastar.
Genetic tests are unable to distinguish O. stellarum found in several
Asterias species and another asteroid, suggesting host specificity may
be low. However, as only a single asteroid species appears to be
parasitized by O. stellarum in any one geographic area, there may be
morphological or ecological attributes that increase host specificity.
"CRIMP is now extending the search for suitable parasites to Korea, in
the hope that additional parasites, perhaps dendrogastrids (highly
modified intracoelomic seastar parasites), may be found at the limit
of Asterias' range. A separate research approach is to find highly
specific reproductive inhibitors - asterosaponins are reported to be
species-specific regulators of gamete release - that can be introduced
into the environment perhaps via transgenic manipulation of a prey
resource, but this research is in its infancy.
A recent article here summarises the results of CSIRO’s work in using
parasites so far:
Thresher, R.E. and N.J. Bax, 2001. Classical Biological Control of the
Northern Pacific Seastar and the European Shore Crab: Prospects for
Success Based on Five Years of Background Work, CSIRO Centre for
Research on Introduced Marine Pests.
(http://sgnis.org/publicat/thresher.htm )
They conclude that:
The results do not rule out the use of either or both parasites to
control introduced populations of their hosts, but do indicate that:
- Clear definition and demonstration of suitable host specificity, and
hence acceptable safety of the release, has been difficult to achieve
for the marine parasites
- The high fecundity of both hosts, in common with many marine
broadcast spawners, dictates extremely high infection levels before
significant reduction of impacts is likely. This may be very difficult
to achieve, and
- The community and government are skeptical of the usefulness and
wisdom of releasing exotic parasites to control even major pests,
despite a general willingness in Australia to use biological control
against a wide variety of terrestrial and aquatic pests.
There is a nice article summarising the whole situation from the
Australian Broadcasting Corporation: "Invasion of the Killer Sea
Stars" here:
(http://www.abc.net.au/science/slab/starfish/default.htm )
It concludes:
"In the meantime, the search for a solution may be a lot closer to
home. Some scientists believe that disturbed environments are more
prone to invasion. In harbours and ports, dredging to improve shipping
channels can destroy native marine communities that are already
weakened by pollution. The building of wharves, piers and pylons gives
arriving stowaways a vacant home as soon as they jump ship. In
Tasmania, a new project (funded by the Natural Heritage Trust) will
investigate the link between disturbed environments and the survival
of the seastars. It will be interesting to see whether the best method
to manage northern Pacific seastars in Australian waters may be to
reduce pollution and enhance local plants and animals in estuaries.
"In the future, molecular biology may be harnessed to attack the
seastars. Scientists could insert or change a gene in northern Pacific
seastars which would castrate them or kill their young. This gene
could be delivered in a bait or by a parasite. For now, it is
important to learn as much as possible about the seastar in Australian
waters - its feeding, reproduction, predators and movements. This
research will hopefully locate an Achilles heel that can be targeted
with these new weapons.
But for now, the battle continues."
The CSIRO Centre for Research on Introduced Marine Pests (CRIMP) is
Australia's national centre for research on the impacts and management
of
introduced marine species.
You’ll find all sorts of info on the sea star here:
(http://crimp.marine.csiro.au// )
Hope that gives you enough to be going on with. If there’s anything
you don't understand, just ask for clarification
willie-ga
New Zealand are also beginning to worry about the possible impact, and
have started to take steps. You can see a paper here:
Ministry of Fisheries Marine Biosecurity ACTION PLAN FOR UNWANTED
SPECIES: Northern Pacific Sea Star
http://216.239.51.100/search?q=cache:8TAvj-Zk0NIC:www.fish.govt.nz/biodiversity/biosecurity/pests/northern_pacific_seastar_action_plan.pdf+%22Asterias+amurensis%22+Tasmania&hl=en&ie=UTF-8
Google search terms used
"Northern Pacific Sea Star" Tasmania control
"Northern Pacific Sea Star" Tasmania
"Asterias amurensis" Tasmania control
"Asterias amurensis" Tasmania
"Asterias amurensis" Tasmania effect
"Asterias amurensis" Tasmania abalone |
Clarification of Answer by
willie-ga
on
11 Nov 2002 07:33 PST
The Sea Star is a voracious predator and will eat almost any animal
tissue it can capture. The sea-star has a particular fondness for
bivalves but it will eat juvenile abalone, whose flesh it eats after
cracking their shells open with its arms. It then pushes its stomach
out through its mouth (located on the underside of its body), coating
the abalone flesh with the stomach and digestive juices before
digesting the prey entirely.
A Scientific survey of the predation effects of the sea star on
Tasmanian marine life was done in 2000
In a report: IMPACT OF THE NORTHERN PACIFIC SEASTAR ASTERIAS AMURENSIS
ON NATIVE MARINE COMMUNITIES IN SOUTH EAST TASMANIA by
Jeff Ross, Craig Johnson and Chad Hewitt
(http://massbay.mit.edu/exoticspecies/conferences/2000/abstracts10.html
)
they said:
"In the Derwent River estuary, where the seastar occurs at high
densities, live adult bivalves are rare, despite the presence in
sediments of numerous remains (intact shells) of adults. Experiments
conducted immediately beyond the current range clearly demonstrated a
large impact of Asterias amurensis on adult bivalve populations. "
"Densities of the commercial bivalves Fulvia tenuicostata and
Katelysia rhytiphora were reduced from upwards of 80 per m2 and 5-7
per m2 respectively, to virtually zero per m2 in treatments with
seastars. Manipulative experiments conducted in the estuary showed
that A. amurensis could have a large impact on bivalve
(replenishment), effectively arresting significant recruitment events.
Densities of F. tenuicostata recruits were reduced by ca. 15 fold in
the presence of seastars at background densities relative to control
treatments without seastars. These results provide strong evidence
that predation by A. amurensis is responsible for the decline, and
subsequent rarity of adult bivalves in the Derwent estuary.
Observations of diet and prey switching show that while the seastar
has clear food preferences, it is a generalist predator able to switch
to other prey when preferred prey (bivalves) become relatively rare."
"The exact nature of the effect of seastar predation on native
communities in southeast Tasmania is site specific given spatial
variability in soft sediment communities. We use the results from our
experimental manipulations, feeding observations and results of our
large-scale surveys to provide a broad synthesis of the immediate and
predicted impacts on native communities, including commercial species.
Our overall conclusion is that at the high densities that can occur in
south east Tasmania, there are large direct and likely indirect
effects on native communities, including several commercial species"
It seems that the Sea Stars prefer bivalves, but will move on to other
seafood, like abalone, when it has cleared the bivalves out.
Unfortunately, the economic impact of the seastar on the abalone
industry has not yet been assessed in any meaningful way. All the
fishermen know that it is a predator, and divers are sent in to clear
it from "farmed" abalone beds, but, the latest policy paper from the
abalone fisheries themselves says on page 58:
"The introduced Northern Sea Star…may pose a threat to abalone through
predation on juvenile abalone…although its importance as an abalone
predator is not clear."
The Tasmanian Abalone Fishery Revised Policy Paper
(http://www.dpiwe.tas.gov.au/inter.nsf/Attachments/ALIR-4Z94F2/$FILE/AbaloneFisheryRevisedPolicyPaper.pdf
)
(The above paper has a great deal of info about the abalone fishery in
Tasmania)
So the fishermen are incurring extra costs in sending down the divers
to clear beds of the starfish, and they know that they are losing at
some of their stock. CSIRO are investigation methods to biologically
and chemically control the starfish, but its population is still
growing, and it may be that in the near futiure it will have
quantifiable effects on the abalone fisheries.
Hope that answers your question, but as ever, if you need more
clarification, just ask.
Willie-ga
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