This document is a report that models the invasive risk potential of the Northern Pacific seastar (Asterias amurensis) in New Zealand waters. It establishes the biological and ecological parameters of A. amurensis in its native and invasive ranges to create a GIS model of its potential suitable habitat in New Zealand. The model suggests areas of New Zealand's coastal marine environment that could be at risk. The report also discusses potential environmental, economic, social and cultural impacts of an invasion, as well as prevention and management strategies.

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Bachelor of Applied Science
(Biodiversity Management)
NSCI 7730 Negotiated Study
Jett Blake
1299619
Modelling the invasive risk potential posed by the
Northern Pacific seastar (Asterias amurensis) in New
Zealand.

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Modelling the invasive risk potential posed by the Northern
Pacific seastar (Asterias amurensis) in New Zealand.
Cover Image- Northern Pacific seastar (Asterias amurensis)-
http://commons.wikimedia.org/wiki/File:%E6%B5%B7%E6%98%9F%EF%BC%88%E6%AD%A3%E9%9D
%A2%EF%BC%89.JPG

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A report submitted in partial fulfilment for the
Bachelor of Applied Science (Biodiversity Management) degree,
Department of Natural Sciences, Unitec New Zealand
November 2010
Suggested citation:
Blake, J. 2010. Modelling the invasive risk potential posed by Northern Pacific seastar
(Asterias amurensis) in New Zealand. Bachelor of Applied Science (Biodiversity
Management).
Unitec Institute of Technology, Auckland. (Unpublished Report).
Department of Natural Sciences
Unitec Institute of Technology
Private Bag 92025, Auckland 1142
NEW ZEALAND

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CONTENTS
ABSTRACT...........................................................................................................................................5
1. INTRODUCTION.........................................................................................................................6
1.1 Risk of Introduction...........................................................................................................................7
1.2 Identifying potential invasive pests....................................................................................................8
2. INVASIBILITY.............................................................................................................................9
3. SPECIES BACKGROUND..........................................................................................................9
3.1 Biology and ecology of the Northern Pacific seastar Asterias amurensis ................................................9
3.1.1 Description................................................................................................................................................9
3.1.2 Life cycle.................................................................................................................................................10
3.1.3 Habitat.....................................................................................................................................................10
3.1.4 Reproduction and growth ........................................................................................................................10
3.1.5 Feeding preferences.................................................................................................................................11
3.1.6 Competitors/ Predators............................................................................................................................11
3.1.7 Invasiveness in Australia.........................................................................................................................12
3.1.8 Dispersal of Asterias ...............................................................................................................................15
4. METHODOLOGY .....................................................................................................................16
5. RESULTS ....................................................................................................................................18
5.1 Ecological suitability of the New Zealand coastal marine environment ................................................18
5.2 Results in relation to individual maps. ...................................................................................................27
5.2.1 Sea Temperatures. ...................................................................................................................................27
5.2.2 Depth.......................................................................................................................................................27
5.2.3 Substrate..................................................................................................................................................27
5.2.4 Current movement...................................................................................................................................27
5.2.5 Overall Suitability. ..................................................................................................................................28
5.2.6 Climate change........................................................................................................................................28
5.2.7 Pathways .................................................................................................................................................29
6. DISCUSSION..............................................................................................................................30
6.1 Effects and Impacts ................................................................................................................................30
6.1.1 Climate Change...................................................................................................................................31
6.1.2 Effects on Native Biodiversity and Ecosystems......................................................................................32
6.1.3 Effects on cultural values ........................................................................................................................35
6.1.4 Effects on production ..............................................................................................................................38
6.1.5 Pathways and vectors ..............................................................................................................................43
6.1.7 Prevention measures................................................................................................................................45
6.1.8 Limitations of this study..........................................................................................................................46
7. CONCLUSION ...........................................................................................................................47
8. RECOMMENDATIONS............................................................................................................49
9. ACKNOWLEDGEMENTS .......................................................................................................50
10. REFERENCES........................................................................................................................51

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11. APPENDICES.........................................................................................................................56
Abstract
Invasive species are defined as ‗alien species whose introduction does or is likely to cause
environmental or economic harm or harm to human health‘ (Meyerson et al 2007). Invasive
marine species have experienced an increased ability to proliferate with increases in global
trade. The Northern Pacific seastar Asterias amurensis is one such species, which has had
serious ecosystem impacts throughout its invasive range in Australia.
Tools such as models of potential invasive risks of a marine species, aim to prevent
introductions by predicting a habitat suitability of a novel environment. By establishing the
parameters critical to survival ( sea surface temperatures, bathymetry, substrate, and currents)
both in its native and invasive habitats, an attempt has been made to construct geographic
information models using GIS with the variables that would allow Asterias amurensis to be
introduced and established in New Zealand waters. An overall suitability model of its
potential invasive range within New Zealand‘s coastal marine environment has been created
as well as the possible potential degradation of environmental, economic, social and cultural
values that could result of such an incursion. Pathways and vectors for a potential
introduction are also modelled as increased economic activity has led to shifting trade
patterns and increased efficiencies in vessels with the resulting increase in the number of
introduced marine species via ballast water. Due to the proximity to Australia this is of high
concern. Therefore, various international and national marine biosecurity legislation and
strategies that have been implemented to aid in protecting New Zealand‘s highly endemic
coastal marine ecosystems and preventing both Asterias and other introduced marine species
incursions are reviewed.

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1. Introduction
The International Union for the Conservation of Nature (2000) define alien invasive species
as ‘species which become established in natural or semi-natural ecosystems or habitat, is an
agent of change and threatens native biological diversity’. New Zealand has a native marine
ecosystem with almost half of the known marine species being endemic (MacDiarmid 2006).
and therefore seeks to protect these species pre-incursion and this is defined in one of the
goals of the New Zealand Biosecurity Councils 2003 strategy as ‗prevention and exclusion:
preventing the entry and establishment of pests and unwanted organisms capable of causing
unacceptable harm to the economy, environment and people’s health’. Mapping potential
invasive species distributions through geographic modelling is a tool then used to evaluate
the likelihood, the biological, cultural and economic consequences, of entry, establishment, or
exposure of these organisms (Holcombe et al 2007). Globalisation of the marine environment
has become a major concern as the number of human-mediated introductions of exotic
species continues to accumulate (Ruiz et al 2000).
The Northern Pacific seastar (Asterias amurensis) is native to Japan, North China, Korea,
Russia and far North Pacific waters (ISSG 2005). Through human mediated factors such as
international shipping and the movement of ballast water from one world ocean to another
this motile species has now become invasive in Australia mainly in two areas- the Derwent
Estuary in Tasmania (population density an estimated three million) and Port Phillip Bay,
Melbourne (population density an estimated 100 million) (University of Melbourne media
release 2001; Biosecurity NZ 2008).

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1.1 Risk of Introduction
Many papers related to alien invasive species as well as international organisations such as
the Convention on Biological Diversity (CBD) have identified that islands such as New
Zealand face a particularly high risk from invasive species over continents due to their
evolutionary isolation in which genetic diversity and population sizes are limited, many of the
food webs and inter/ intra specific relationships are generally simplistic, and have become
density dependant due to lowered carrying capacities of area and niches available (CBD
2009). These species also tend to show gigantism, dwarfism, and loss of dispersability and
defence mechanisms in the absence of predators (CBD 2009).
The marine ecosystem is particularly susceptible to alien species invading as it is harder to
detect and monitor activity in the underwater environment where there are no clear defined
borders such that between terrestrial and marine environments. The New Zealand coastal
marine ecosystem therefore faces an even higher risk as it is also an environment given to
high disturbance. Sea temperatures, substrate type, bathymetry and tidal movement are
usually major‘s parameter influencing a marine species ability to invade and survive in a new
environment (Summerson et al 2007).
With the increase of international trade and movement between countries and the movement
of ballast water from different oceans of the world to others, the risk of moving exotic species
into novel environments is being realized. New Zealand has the fourth largest exclusive
economic zone (EEZ) in the world at 4.1 million square kilometres (MFish 2007), and the
need to protect the complex biodiversity and resources contained within this area is
imperative. However, it is important to note that not all introduced marine invasive species
are considered pests due to their commercial value and are to some degree tolerated. For

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example the Pacific oyster (Crassostrea gigas) is farmed as a commercial product in the New
Zealand aquaculture industry. It has overtaken the native New Zealand rock oyster
(Saccostrea glomerata) as it has a faster growth cycle, and has replaced this species both in
oyster farms and in the wild (Troup 2009). Although in natural environments the Pacific
oyster can change the ecology of intertidal rock platforms, by forming dense clumps that
accumulate mud, changing the character of the substrate. Also, they impact on recreational
use of beaches as their shells break into sharp fragments, making these areas less appealing.
Also it is believed through imports of the Pacific oyster that the clubbed tunicate Styela clava,
another invasive marine species was introduced to New Zealand (Troup 2009).
1.2 Identifying potential invasive pests
The Northern Pacific seastar Asterias amurensis (hereafter referred to as Asterias), is labelled
as one of the world‘s worst invasive alien species due to its wide range of tolerance to
varying marine conditions (ISSG 2005) and poses a major threat to New Zealand‘s marine
environment, Maori cultural values and the aquaculture industry (Biosecurity Strategy 2003).
This is attributed to although the species having preferred suitability conditions and
requirements it has shown through becoming established in Australian waters which has sea
temperatures considered out of the range of habitation for this species, that it has a wide
range of tolerance to varying marine conditions (CSIRO 2005; Summerson et al 2007).
The aim of this project is to identify the ecophysiological characteristics of Asterias that
would allow it to become invasive in New Zealand coastal waters. Its potential of becoming
established and categorize high- low risk areas of the New Zealand coast where it would
likely to become established and identify the most probable pathways and points of entry into
New Zealand, and potential impacts of this species on the coastal marine environment and

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how this will further impact on cultural values and economic development will be addressed.
Finally means of protecting New Zealand waters and preventing introduction of the starfish
will be reviewed.
2. Invasibility
Invasive species are defined as ‗an alien species whose introduction does or is likely to cause
environmental or economic harm or harm to human health‘ (Meyerson et al 2007). In
general, life histories and habitat preferences of invasive marine species are not well
understood and only a few have been subjected to comprehensive study. Those that have
been studied in detail such as Asterias have shown that they are adaptable and able to tolerate
conditions in new environments that are outside the tolerance range in their native
environments. Many invasive marine species have these extensive habitat tolerances. It is this
characteristic that enables them to adapt rapidly to novel environments (Simberloff &
Alexander 1998).
3. Species Background
3.1 Biology and ecology of the Northern Pacific seastar Asterias amurensis
3.1.1 Description
The Northern Pacific seastar Asterias amurensis is a large echinoderm in the family
Asteriidae with a small central disc and five distinct arms that taper to pointed tips (NIMPIS
2010). It is predominantly yellow in colour and often seen with purple or red detail on its
upper surface. There are numerous small spines with sharp edges on the upper body surface
that are arranged irregularly along the arm edges. On the underside of the body, these spines
line the groove in which the tube feet lie, and join up at the mouth in a fan-like shape. The

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underside is a uniform yellow in colour. Its native range is the far north Pacific waters and
areas surrounding Japan, Russia, North China, and Korea (NIMPIS 2010; CSIRO 2009).
3.1.2 Life cycle
Time to reach maturity takes 365 days around which time the 5cm individuals become
sexually reproductive (Turner 1992). A single female can release about 20 million eggs
which, when fertilised, move with tides and currents for 6-16 weeks before settling to the sea
floor. Size at maturity is estimated at 3.6-5.5cm (Nojima et al 1986). Arm Morphology
Length of Asterias in Tokyo Bay was 46mm for female and 47 mm for males at maturity
(Kim 1968). Arm Morphology Length of Asterias in Mutsu Bay was 55 mm for male and
female seastars at maturity (Kim 1968). Fully grown individuals can reach 40-50 cm in
diameter (ISSG 2005).
3.1.3 Habitat
Asterias is mainly found in sheltered localities such as coastal areas that are protected from
exposure and high wave action. It is found in intertidal and subtidal zones and in its native
Japan it has been recorded at depths of 200 metres (NIMPIS 2010). In Australia however, it
has not been found at such depths, but on shallower soft sediment (silt and sand-coarse) and
rock habitats above 25 metres. Adult survival parameters for temperature is between 0.0 °C-
25.0 °C and for reproduction, larval survival and development range is between 5.0°C- 23.0
°C (Kim 1968; Novikova 1978) (see appendix 1).
3.1.4 Reproduction and growth
Asterias is capable of both sexual and asexual reproduction. Males and females are separate
and release eggs and sperm into the water during winter. Females are capable of producing
10-25 million eggs per year. Fertilisation is external, and larvae can remain in the water
column for about 120 days (Kim 1968). The seastar is also capable of regeneration. Asexual

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reproduction is only possible if part of the central disc of the seastar is attached to the broken
arm (McLoughlin et al 1994; Ward & Andrew 1995). The growth rate of Asterias is
approximately 6mm per month in the first year, after which growth slows to about 1-2 mm
per month. Breeding occurs in Japan between January- April and peaks in late February-early
March (Ino et al 1955), and in Tasmania this occurs between July-Oct. (Hawkes et al 1993).
3.1.5 Feeding preferences
Asterias is a carnivore and an opportunistic predator depending on the food that is available
(Turner 1992). Typically it feeds on large bivalves such as mussels, scallops and clams, as
well as gastropods, crabs and barnacles. It has been observed feeding on dead seastars and
fish and is an opportunistic cannibal at times (Davenport & McLoughlin 1993) and capable of
digging shallow pits in search of prey (Hawkes & Day 1993). Recent work in Tasmania has
shown that while Asterias is a generalist predator, it has clear food preferences for bivalves
(including several commercial species) that live on or just below the sediment surface (Ross
et al 2002). Experimental and field trials in Victoria showed that Australian scallops
displayed predator naivety to Asterias whereas low frequencies of escape response were
observed compared to native seastars such as Coscinasterias muricata (Hutson et al 2005).
The size of the prey usually equals the length of the seastar's arm (Kim 1969; Turner 1992).
Asterias is also capable of stripping algae from the seabed (Turner 1992).
3.1.6 Competitors/ Predators
In its native Japan, Solaster paxillatus (a sunstar) has been noted as a predator of Asterias. In
laboratory experiments in Korea, Charonia sp. (a trumpet shell) was seen to prefer Asterias
as their prey over other sea stars, sea cucumbers and sea urchins. The predation of Asterias by
king crabs in Alaskan aquaria has also been observed. Competitors include Uniophora
granifera, Coscinasterias muricata (Morrice 1995) as well as the Pacific walruses Odobenus

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rosmarus divergens (Fukuyama & Oiver et al, 1985). However whether some of these
species can or will be used as biological controls is in question as prey switching to non-
target species cannot be guaranteed (ISSG 2005).
3.1.7 Invasiveness in Australia
Asterias is thought to have been introduced to Tasmania via the ballast tank water from an
overseas cargo ship in 1986. At the time the seastar was incorrectly identified as a native
species. It wasn‘t until 1992 that the star was correctly identified as an introduced species
(CSIRO 2005).
The seastar is now invasive in South-eastern Australia including Tasmania and Victoria
(CSIRO 2005). Since its invasion it now occurs in densities of up to 100 million (Goggin
1999). In a two-year study undertaken by the Commonwealth Scientific and Industrial
Research Organisation (CSIRO) for the Department of Environment and Heritage (Australia)
to identify and rank introduced marine species found within Australian waters as well as
potential invasives. All of the non-native potential target species identified in the report were
ranked as high, medium and low priority pests, based on their invasion potential and impact
potential (Hayes et al 2005). Asterias was identified to be one of the ten most likely potential
damaging domestic target species, based on its overall impact potential both environmental
and economic. The ranking of these potential domestic target species was based on invasion
potential from infected to uninfected bioregions, and identified Asterias as a 'medium
priority species' - these were species have had a considerably high impact/or invasion
potential (CSIRO 2005;Hayes et al 2005; ISSG 2005).
Further GIS modelling to predict potential distribution within Australia has also been carried
out by the Australian government in its report ‗Invasive Marine Species Range Mapping‘
where it has identified SST as the main critical limiting factor on Asterias larval distribution
and mapped the outcome of this study.

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As species that are pests in one situation are likely to be a pest in others (McNeely 2004), as
even within its native range of Japan, Asterias has become a pest, with threats being posed to
the seafood industry. Where it has spread to in Australia, it has seriously affected native
shellfish populations. Where densities of the seastar are high (such as in the Derwent
estuary), many bivalves and other attached or sedentary invertebrates have been eliminated.
Asterias has further contributed to the decline of the endangered spotted handfish (NIMPIS
2008) as it preys on its egg masses as well as the Ascidean Sycozoa pulchra, which the
spotted handfish uses as substrate to lay its eggs around (Roberts & Hawkins 1999).
This species features on the ISSG‘s database as one of the worlds 100 worst invasive pests. In
Australia, it took approximately 15 years after initial introduction and discovery for the
species to reach pest status (between the mid 1980‘s -1995). As the species to date has only
Summerson et al 2007

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become invasive in Australia, there have been efforts to eradicate it in the Derwent estuary
where it is estimated to occur in the highest densities of anywhere in the world (CSIRO
2005). Although within its native range it is known to go through ‗boom and bust‘ cycles
(ISSG 2010). It is however now considered ineradicable in Australia; however, management
attempts to focus on excluding the species from other parts of the country (CSIRO 2005).
Control methods have included physical removal of Asterias by divers (NCP 2008).
However small scale operations (between 6000- 24000 individuals removed) have proved
ineffective as pre- and post- population studies indicated negligible effects of physical
removal as a management tool as within two months, populations at one site had recovered to
the pre-removal densities, while another site only showed a slightly lowered population
compared to pre-removal surveys (NIMPIS 2008). Dredging has been considered as a
potential physical removal method as it has been used in Japan to reduce Asterias densities
around fish farm operations (Ito 1991). However, its environmental impacts have been
considered unacceptable, especially in the Derwent River as re-suspension of heavy metals in
bottom sediment could have serious consequences on ecological and human health (NCP
2008). Biological and chemical control methods are also currently being investigated, the
ciliate Orchitophyra stellarum (a ciliate disease of sea stars) is the most likely candidate for
biological control of the species (Goggin 1998). However, its capacity to control Asterias
populations remains uncertain. Also, its ability to infect other species in the asteroid genera
has raised serious concerns in relation to potential impacts on non-target species. Chemical
controls including broadcast application of chemicals, direct injection and application of
chemicals that interfere with reproduction have been considered to reduce Asterias
populations (Goggin 1998). However, for large scale management of established Asterias
populations these methods are considered somewhat unlikely to be utilized due to
environmental concerns (NIMPIS 2008).

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3.1.8 Dispersal of Asterias
There are two ways in which Asterias larvae are transported to a new environment either
 Natural dispersal or;
 Human-mediated introduction (NCP 2008).
Natural dispersal is a mechanism for the range expansion of a species through natural
processes such as the movement of larvae or adults to a new location (NIMPIS 2010). Either
through passive movement in water currents or active migration movement in response to
changes in environmental conditions such as salinity changes or water flow dynamics.
Natural dispersal may also allow for higher successful settlement of recruits in a new location
(NIMPIS 2010).
Human- mediated introduction can include international vessel movement as a vector
comprising of commercial ships e.g. tankers, container ships, ferries and barges as well as
fishing vessels, recreational vessels, passenger vessels, drilling platforms and research
vessels, through their combined use of ballast water, dry ballast and as hosts to biofouling
communities (NIMPIS 2010).
Asterias falls into the later for intra-oceanic introduction into Australia, specifically through
contaminated ballast water, which has been found to transport up to 10,000 different species
at any one time (Bax 2003). From its initial introduction in Tasmanian waters to where it has
also become invasive in Victorian waters specifically Port Phillip Bay, where individuals
through DNA sampling showed that Asterias was naturally dispersed was moved via water
columns from Tasmanian (NIMPIS 2010).

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4. Methodology
In developing the methodology for the assessment of the potential range of a new invasive
marine species, the first step was to compile information about the life histories and
environmental tolerances of the species. Then combining this information to New Zealand
with geographic and climatic data gathered from a wide range of both local and international
agencies (including but not limited to Biosecurity NZ, NIMPIS and CSIRO) geographic
information systems (GIS) was used to analyse data in direct relation to the Northern Pacific
seastar Asterias amurensis.
Literature research on the sea stars invasiveness in Australia and how this seastar is
introduced to new environments and modes of transportation to novel regions was also
researched. Biosecurity New Zealand and the Ministry of Agriculture and Fisheries were also
used to ascertain whether this species had been intercepted at the border as well as the
probability of it surviving within water columns over long haul voyages.
Literature search supplied information as to the sea stars ecophysiological requirements and
methods of dispersal and how these have enhanced its ability to become invasive elsewhere
(Australia). As an invasive species is defined as a non-native organism that cause, or have the
potential to cause harm to the environment, economies and human values. Literature research
will also be undertaken to assess possible impacts in these areas, by comparison to invaded
regions.
Factors/ variables that would allow the Northern Pacific seastar to become invasive were
determined. From literature research, the criteria that heavily influenced potential
establishment and entrenchment were sea temperatures, substrate type, ocean gradient and
tidal movement and wave action.

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Using these ecological factors and associated data available through the National Aquatic
Biodiversity Information System (NABIS) geographic modelling was then used to model
these variables directly against New Zealand abiotic data. Using the information obtained,
each of these variables was then divided into a range of values relative to their suitability for
the survival and success of this seastar in New Zealand waters. This was achieved by using
ARCMap software to initially model all variables and then reclassify them according to
suitability for survival. These were then ranked from 1-5, 1 being areas of low/ lower
suitability and 5 being high/ higher in suitability and then all variables were added to produce
an overall suitability map with eliminated unsuitable areas for habitation. For example;
Annual amplitude SST Suitability Ranking
0.1-0.8 Least suitable 1
0.8-1.6 2
1.6-2.3 3
2.3- 3.0 4
3.0-3.9 More suitable 5
The International Panel for Climate Change (IPCC) site was used to assess the information
obtained in relation to predicted increases in sea surface temperatures and produces a climate
change model, and pathways of entry model was also produced.
A further three maps were created using data obtained from NABIS to display the potential
and the areas which would be impacted such as marine reserves, cultural harvesting and
aquaculture. The ability to control Asterias if it were to be introduced to New Zealand is
another major factor therefore preventing introductions will be discussed. By using existing
literature, information was obtained regarding New Zealand and international legal

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requirements, policies and procedures in order to protect its borders against invasive marine
organisms which carry severe ecological impacts.
5. Results
5.1 Ecological suitability of the New Zealand coastal marine environment
The main abiotic actors that would allow distribution of Asterias are sea surface temperatures
(SST), bathymetry, substrate type and current movement and introduction pathways. Climate
change (increases to SST), also allows further localised distribution and establishment of this
species in a new environment.
In this section the suitability of New Zealand‘s coastal marine environment to an introduction
of Asterias is modelled. The results are displayed as GIS maps for easy visualisation.

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5.2 Results in relation to individual maps.
5.2.1 Sea Temperatures.
Map 1 displays the suitability of New Zealand areas in relation to annual amplitude SST,
which is a critical factor of high value for environmental suitability. From the map it is shown
that at present there are no areas that are suitable for distribution of Asterias larvae. While the
sea temperatures are in the lower range of the known survival suitability for adult individuals,
the rest of the coastal marine waters are too cold for larvae to survive as well as reproduction
to occur.
5.2.2 Depth
Map 2 displays the suitability of New Zealand areas in relation to bathymetry. From the map
it is shown that at present there are vast areas that are suitable for habitation by Asterias.
Particularly noticeable are those within the various North Island Harbours (Kaipara,
Manukau, Waitemata and Wellington) and the East coast of the South Island.
5.2.3 Substrate
Map 3 displays the suitability of New Zealand areas in relation to substrate. From the map it
is shown that at present there are vast areas that are suitable for habitation by Asterias.
Particularly of high suitability were Gravel/sand and Volcanic sediments substrate. While
some substrate types might influence Asterias densities, there generally is widespread
substrate suitability throughout the New Zealand coastal intertidal areas.
5.2.4 Current movement
Map 4 displays the suitability of New Zealand areas in relation to tidal movement. From the
map it is shown that at present there are vast areas that are suitable for habitation by Asterias.
High tidal movement occurs around Cape Reinga, the Cook Strait and between Stewart Island
and the mainland. The tidal contours also indicate that if Asterias were to be introduced into

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New Zealand there is also a threat posed to outer Islands which feature highly on New
Zealand‘s conservation priorities, increasing its threat potential.
5.2.5 Overall Suitability.
The results of the suitable depth, substrate types, tidal movement and surface temperature
analyses were combined by adding the ranking values of each maps layer to form an
inclusive overlain map (Map 5) which shows the most suitable environment for the Northern
pacific seastar by combining these variables. As every location has a ranked value between 1-
5, which ranges from lower to higher suitability, due to unsuitable temperatures (limiting
critical factor) for larvae development and dispersal, there are no optimal conditions for
invasiveness within New Zealand for larvae, however the overall combination of factors are
suitable to support adult Asterias, particularly in the Waitemata and Manukau harbour,
Kaipara harbour and along the west coast of the North Island and the east coast of the South
Island. However as Asterias is highly invasive in Australia, where lower temperatures were
considered to be out of its range, it has proven to be highly adaptable and tolerant to a wide
range of conditions in a new environment (NIMPIS 2008).
5.2.6 Climate change
Map 6 displays the predicted increase in SST. Although there is no change in the extent of
SST suitability, this increase puts SST within the known values for successful survival and
dispersal of Asterias larvae in Australia and therefore climate change is the most serious
threat to successful establishment of Asterias in the New Zealand coastal marine
environment.

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5.2.7 Pathways
Map 7 displays the most probable pathways of entry of Asterias into New Zealand. The
graduated symbols denote the number of international vessel arrivals by port. This map
shows that the ports with the higher vessel arrivals present the highest potential introduction
risk such as the ports of Auckland, Tauranga and Nelson.

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6. Discussion
6.1 Effects and Impacts
The New Zealand‘s coastal environment is inhabited by an estimated 65,000 species, many of
which are either endemic or native to New Zealand, making these ecosystems a hotspot for
worldwide marine diversity (Arnold 2004; MacDiarmid 2007). As these ecosystems and their
inclusive species deliver a wide range of environmental services to New Zealand including
basic productivity that sustains the large scale ecotourism, fishing and aquaculture industries
(Biosecurity 2009), an introduction of a highly invasive species such as Asterias will have
serious results for every sector.
Much of the New Zealand marine habitat is suitable for adult Asterias, albeit within the lower
survivability of the species tolerances. The results of this study and the overall suitability
model suggest that while individuals of the species may survive within New Zealand‘s
coastal environment, it most probably will not be able to establish a large population here due
to temperature constraints. However, the main concern lies with the result of the climate
change model, as it has been shown that with increases in SST this could allow for a
successful reproducing population that could expand into areas that are currently now
considered suboptimal for Asterias.
The main impacts identified within Asterias invasive range have been domination and
competitive behaviour that could limit the availability of natural resources for native species
as well as impacts and loss of recreational, commercial and aquaculture harvests (Hayes et al
2003) and these will be discussed in relation to the New Zealand environment.

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6.1.1 Climate Change
Individually, climate change and invasive species present two of the greatest threats to
biodiversity and the provision of valuable ecosystem services (Burgiel & Muir 2010). As the
results show, the New Zealand coastal marine ecosystem currently does not present the
optimal temperatures for the reproduction and dispersal of Asterias larvae, however future
predicted changes in climate has shown a higher suitable invasive range for Asterias. By
providing suitable temperature for reproduction as well as dispersal, while possibly affecting
ranges and survivability of other native specialist organisms (Simberloff 1997). Climate
change impacts, in particular warming sea temperatures and changes in CO² concentrations,
are more than likely to increase opportunities for invasive species because of their
adaptability to disturbance and to a broader range of biogeographic conditions and
environmental controls (Burgiel & Muir 2010). The impacts of invasive species such as
Asterias may be more severe as they can increase exponentially both in numbers and extent,
and present high competition for diminishing resources such as food and suitable habitat.
Increases in water temperatures are predicted to facilitate movement of species along
previously inaccessible pathways of spread, both natural and human-made (Burgiel & Muir
2010; WWF 2009).
The International Panel for Climate Change (IPCC) predicted increase in sea surface
temperatures (SST) by 2100 is an estimated rise of between 1.4-5.8° C (Mimura et al 2007).
Although this figure is dependent on a number of variables, the average of this prediction the
figures are a 2.2° C increase in SST. The climate change model showed that with climate
change, New Zealand will present suitable conditions for Asterias larvae to survive and
disperse almost entirely along the New Zealand coast. This increase in temperature may also
impact on the survivability of New Zealand coastal marine organisms and result in a decrease

32. 32
in their original ranges. This may further impact endangered native marine species and well
as allow for competitive displacement of New Zealand‘s highly endemic marine populations.
6.1.2 Effects on Native Biodiversity and Ecosystems
New Zealand has a wide and varied marine ecosystem made up of diverse and native benthic
fauna. The level of endemism among bivalves and gastropods is extremely high; with 85.5%
(589) of bivalves and 86.6% (3183) of gastropods found only in New Zealand (MacDiarmid
2006). Some groups show particular speciosity, for example within the families
Spheniopsidae and Trochaclididae are the majority of the world's bivalves and the glass-
sponge eating gastropods respectively found in New Zealand. New Zealand's bivalve and
molluscan fauna show a distinctiveness which is characterised by certain taxa. Several
species are the largest or among the largest of their group worldwide which may be an
evolutionary response in the absence of predators (MacDiarmid 2006). The toheroa is one of
the largest in its family, the Mesodesmatidae, several of New Zealand's gastropods are larger
than any others worldwide; and the giant Kermadec Island limpet, the only representative of
its family in New Zealand, reaches 150 mm in length (MacDiarmid 2006). The impacts that
Asterias could have on these species especially bivalves would be high as it could establish
itself as a dominant opportunistic carnivore with few predators. Although there are few
endangered benthic fauna (e.g. Toheroa Paphies ventricosa), other marine organisms are only
known to be found in one location and subjected to other population pressures such as
overharvesting except within established marine reserves and parks and the introduction of
Asterias may drive these species to small extant populations .
Many of the established marine reserves and parks in New Zealand occur in close coastal
proximity to the mainland and shoreline with the exception of the Kermadec and Auckland

33. 33
islands marine reserves (DOC 2010). The first New Zealand marine reserve and one of the
world‘s first no-take marine reserves (Cape Rodney – Okakari Point Marine Reserve) was
established in 1975 and there are now over 30 marine reserves established in New Zealand
waters (DOC 2010). Collectively, these reserves protect 7% of New Zealand‘s territorial sea.
However, 99% of this is in two marine reserves around isolated offshore island groups
(Auckland and Kermadec).
Of New Zealand‘s total marine environment, only 0.3% is protected in marine reserves. The
highest level of protection outside of New Zealand‘s Territorial Sea is through closures on
trawling by fisheries for 18 seamounts. The inclusion of these closures brings the area of
marine protection in New Zealand‘s marine environment to just over 3% (DOC 2010).
Asterias therefore poses a large threat to native marine biodiversity, as the overall suitability
model overlapped most of the marine reserves and parks as high potential invasive risk areas.
As the potential invasive areas identify many harbours as high potential risk areas this also
has implications for fish which use sheltered areas within harbours such as mangroves for
reproduction and as Asterias has been shown to prey on egg masses (NCP 2008), this may
further impact species such as snapper which face threats from other human activities such as
fishing and water pollution. Displayed in the following map is the location of coastal New
Zealand marine reserves and parks which would be threatened by an invasion of Asterias.

34. 34

35. 35
There would also be implications for human amenity values as marine reserves bring in
important revenue for the ecotourism sector and as over half of these marine reserves were
lodged by interest groups including tangata whenua, conservation groups, fishers, divers and
marine science interest groups (DOC 2010). A potential invasion by Asterias could also
implications for scientific and recreational and cultural use as well.
New Zealand scientists have identified in total 159 alien marine species (Cranfeild et al 1998)
however Asterias (and other invasive species) do more than just drive native species to
extinction: they change ecosystem processes and structure, alter genetic diversity, and reduce
local biodiversity (Donlan 2010).
The numerical dominance of invasive alien marine species such as Asterias swamp native
species and alter ecosystem services. Three of the six most common benthic marine species
in Port Phillip Bay in 1996 were alien species, though this did not include Asterias, which has
increased to over 100 million individuals covering 1500km² and has a greater biomass than
that of all fished species in the Bay (Bax 2003).
6.1.3 Effects on cultural values
Mäori play an important part in the use and management of the coastal marine environment
under Mataitai and Taiapure areas established under Article II of the Treaty of Waitangi.
Mataitai, taiapure and temporary closures provide for customary Mäori use and management
practices in areas traditionally of importance to Mäori (Wakefeild et al 2005). Within
mataitai reserves, tangata whenua manage all non commercial fishing including shellfish
collection by making bylaws. Taiapure areas are established to give local Mäori the ability to
recommend regulation to manage all types of fishing (Wakefeild et al 2005). Traditionally
and historically Maori fish and collect seafood (kaimoana) as part of their diet. However the
potential invasive range for Asterias encompasses most of these coastal areas as displayed in

36. 36
the following map. Along these intertidal areas Mäori harvest kaimoana which include
shellfish such as:
Pāua (Haliotis iris)
Kina (sea urchins or Evechinus chloroticus)
Pipi (Paphies australis)
Tuangi (cockles or Austrovenus stutchburyi)
Tuatua (Paphies subtriangulata) native
Kuku or kūtai (Mussels or Perna canaliculus) native
Tio (native rock oysters or Saccostrea cucullata) and Bluff oyster (Tiostrea chilensis lutaria)
Toheroa (Paphies ventricosa) endangered
Pūpū (cat‘s eyes or Turbo smaragdus)
Whetiko (mud snails or Amphibola crenata)
Kaikaikaroro (triangle shells or Spisula aequilatera) native (Whaanga 2009)
The results of this study on Asterias show that there would be a high potential risk to
culturally important coastal areas and species which are of high inherent value to Mäori as
taonga. Although species which favour habitat with high wave action such as toheroa may
not be as threatened as this is a limiting factor for Asterias establishment. Within its invasive
ranges in Australia the seastar has shown to be an opportunistic predator with a high
preference for bivalves and other intertidal species and caused widespread elimination of
other benthic fauna where it had become invasive (Lockhart 1995). The following map
identifies the areas of mataitai and taiapure that fall within the potential invasive range and
would potentially be threatened by an incursion of Asterias, which could have potential
cultural implication for Mäori tikanga and their continued way of life as the cost to customary
harvest values cannot be quantified (Biosecurity Strategy 2003).

37. 37

38. 38
6.1.4 Effects on production
New Zealand has a large developing aquaculture industry, these marine farms have been
established in the last 30 years, in close inshore areas such as harbours and sheltered bays for
both ease of management and protection from extreme weather conditions (AQNZ facts
2010). New Zealand cultivated species are:
 The native New Zealand green lipped mussel (Perna canaliculus)
 The introduced Pacific oyster (Crassostrea gigas) and
 The introduced King Salmon (Chinook salmon Oncorhynchus tshawytscha)
(AQNZ facts 2010)
Aquaculture exports in 2008 equated to NZ$265 million. Of this Green lipped mussel
contributed 86% (33,296 tonnes), King Salmon 9% (3,479 tonnes) and Pacific oysters 5%
(1,873 tonnes) toward total aquaculture exports for the year (AQNZ facts 2010).
The following graph illustrates the breakdown of the major aquaculture growing areas and
total production for the year 2008-

39. 39
Currently in New Zealand aquaculture takes place in approximately 15,800 hectares of
allocated water space, of this 43% of located in near shore sites and 53% are in open water
sites (AQNZ 2010). However most open water sites are still in developmental stages and as
these sites face higher exposure, structures differ from near shore sites and tend to be smaller,
leading to lower stocking capacities and i.e. lower yields (AQNZ 2010).
The impacts that Asterias could have on these species and production would be vast
especially for mussels and oysters as Asterias has shown prey preference for bivalves. Within
its native range of Japan, Asterias has caused considerable damage to commercial shell
fisheries such as oysters, cockles, scallops and other clams (Hatanaka et al 1959; Kim 1969;
Nojima et al 1986). The successful establishment of Asterias in southeast Tasmania has
affected native benthic marine communities and commercial species, particularly bivalves
(Lockhart 1995, Grannum et al 1996). In Tasmania, indirect indications of impact from
observations of seastar foraging behaviour, stomach contents and estimates of feeding
electivity suggested considerable impacts of Asterias on native species (Ross et al 2002),
particularly bivalves (Morrice 1995; Grannum et al 1996; Lockhart et al 2001) farmed for
commercial purposes such as Fulvia tenuicostata (a cockle) and abalone (New Zealand
Paua). Also, live bivalves >5 to 10 mm are rare in areas where the seastar is now abundant
(Domisse et al 2004). Species currently farmed in Tasmania include abalone, blue mussels,
Pacific oysters, rock lobsters, and salmon and sea horses (Larcombe et al 2002). There have
been reports of very large numbers of Asterias in scallop spat collector bags and suspended
'grow out 'cages near Triabunna, Tasmania (McManus et al 2001). Asterias have been
reported from mussel long-lines in Port Phillip Bay (Goggin 1998) and oyster trays in Pipe
Clay Lagoon, Tasmania (Martin and Proctor 2000). The size of the seastars varied from
recently settled juveniles (3-4cm in diameter) on mussel lines to pre-productive adults in

40. 40
oyster trays. It is believed that, in all cases, settlement from plankton directly onto the
different gears used is the most likely origin of the seastars (Martin and Proctor 2000).
Hickman (1998) in a survey of aquaculture farmers in Port Phillip Bay found that control
methods such as trapping Asterias in specially designed benthic traps had no success but
farmers found numerous juveniles on nearby mussel ropes. In Pipe Clay Lagoon, both native
and Asterias are actively removed from aquaculture gear (DPIWE 1998). In Tasmania and
Victoria, divers are employed to clear sea stars from aquaculture farms (Domisse et al 2004).
(Domisse et al 2004)
This ability to attach to mussel ropes would have dire consequences for mainly the mussel
farms and oyster farms as the salmon run and reproduction occur in freshwater where
Asterias cannot survive.
Another threat to the green lipped mussel in the wild and commercially would be potential
impacts on spat collection. New Zealand green lipped mussel farms rely heavily on the
production of mussel seed, or spat by wild mussel populations (Alfaro et al 2001). Around
270 tonnes of wild spat which is attached to beach-cast seaweed is collected from Ninety-
Mile Beach in northern New Zealand each year to supply the aquaculture industry (Alfaro et
al 2003; Loyd 2003). The density of spat varies from 200 to 2 million per kilogram of
seaweed (Alfaro et al 2010). This single beach provides around 80% of the seed mussels

41. 41
required for this aquaculture industry (Alfaro et al 2001). The remaining 20% is caught using
fibrous ropes which are suspended in the sea near mussel farms (Carton et al 2004).
There would be high consequences for both wild and farmed populations as all of ninety-mile
beach is encompassed in the potentially high risk areas for invasion by Asterias. If it was to
become widespread in New Zealand, shellfish stock is estimated to experience a reduction
between 10 – 50% (Biosecurity Strategy 2003). Also in the following map it is important to
note that aquaculture may actually bear the brunt of early introductions due to their locations
which all fall within the potential high risk invasion areas and are in close proximity to
international ports therefore increasing the impacts of Asterias on the aquaculture industry.

42. 42

43. 43
6.1.5 Pathways and vectors
The ability of Asterias to reach the New Zealand marine environment and disperse is directly
linked to habitat suitability and based upon previous introduction methods in Australia, the
most probable pathway for an incursion into New Zealand has been identified as the
international ports of first arrival with ships ballast water as the main vector. Due to the close
proximity of the two countries as well as increasing global trade there is high possibility of
incursions if stringent controls are not constantly enforced. Once Asterias larvae are
introduced here, natural dispersal through water currents will spread it along the New
Zealand coast from the point of origin. From the results it has been identified that large ports
with high volume of international ship movement pose the higher risk such as Auckland,
Tauranga and Nelson (see appendix 2). However the smaller ports with low vessel arrivals
should not be discounted as some have high habitation suitability (e.g. Lyttleton) and can still
present a high potential invasive risk even if there was only to be a few initial Asterias larvae
introduced. The results of annual international vessel arrivals have been summarised in the
graph below-

44. 44
Although there are other vectors in which Asterias could be introduced including water held
in sea chests on vessels and the global live marine fish pet trade. The risk associated with
these vectors are not as considerable as ballast water which due to constant injection rates and
the vast volumes associated with international ships, pose the greatest risk for potential
introduction. Global shipping moves 80 percent of world commodities (Tamburri & Wasson
& Matsuda 2002). This is reflected in the annual international vessel movement into New
Zealand in 2006 totalling 3355. Considering Asterias larvae remain in the water column for
120 days and the average voyage between the eastern Australian coast and New Zealand is
approximately only 5 days (Rother 2010), larval survival rates may be high. Ballast water
amounts are of considerable large proportions, especially for non-cargo ships. For example,
large tankers can carry in excess of 200,000 m 3
of ballast water and rates of pumping can be
as high as 15,000 to 20,000 m 3
/h (Russel 2004).
International trade vessel movement (Biosecurity NZ).

45. 45
6.1.7 Prevention measures
Domestic and international restrictions on ballast water exchange have been applied to
vessels based on the marine pests present in the port where ballast water was taken up.
Due to the Asterias presence in Tasmania, authorities in Port Phillip Bay (Victoria) and New
Zealand declared that ballast water from Tasmanian ports was too high a risk to accept. These
ports do not allow ships to discharge ballast water originating from Tasmania in their waters
(Biosecurity NZ 2010). However these measures were not enough to prevent an invasion in
Port Phillip Bay where Asterias is now highly invasive (Biosecurity NZ 2010).
New Zealand has in place biosecurity arrangements to protect its waters pre-border, in the
form of national legislation. There are two legislative acts that address the introduction of
new alien species. These are the Biosecurity Act 1993 which addresses keeping unwanted
species out of the country and the Hazardous Substances and New Organisms Act 1996
(HSNO) which addresses assessments of species where an intentional introduction is being
proposed. In the more recent 2003 Biosecurity Strategy, Asterias is profiled and classed as an
unwanted species in New Zealand waters (Biosecurity Strategy 2003).
Worldwide the threat of invasive marine species such as Asterias have had a high response as
through international trade, trade vessels now come under both national and international
standards.
To reduce the risks of introductions of invasive species, the International Maritime
Organization (IMO) has adopted the International Convention for the Control and
Management of Ships‘ Ballast Water and Sediments in 2004 when, once ratified, will require
all vessels to carry out standardised ballast water management. The treatment standard is
based on an allowable discharge of viable organisms within specified size categories which
will be phased in over time (IMO 2005). During the phasing in time, all vessels will be

46. 46
required to undertake ballast water exchange in waters more than 200 nautical miles from
land and in waters deeper than 200 metres, although, when this is not possible such as during
extreme weather, part of the convention allows for vessels to exchange their ballast in waters
50 nautical miles from land and 200 metres deep (IMO 2005).
This preventative measure involves ballast water taken on in port being exchanged for deep,
oceanic water and is based on the assumption that coastal organisms will not survive in
oceanic waters and organisms picked up during the exchange process will not survive in
coastal waters, therefore reducing the overall invasive risk (IMO 2005; ref).
This is well summarised by the United Nations Convention on the Law of the Sea
(UNCLOS) where-
―measurements must be taken to prevent, reduce, and control the intentional or accidental
introduction of species, alien or new, which could cause significant and harmful changes to
the marine environment‖ (UNCLOS 1982).
6.1.8 Limitations of this study
In order to improve the accuracy and validity of this potential invasive risk model for
Asterias in New Zealand, a wave action map needs to be modelled, as well as projected
increases in sea level around the New Zealand coast. Due to data restrictions and time
limitations of this research project, these have not been modelled as part of the results and do
not feature in the overall suitability model for the potential invasive risk posed by Asterias,
though these have been discussed briefly within the effects section.

47. 47
7. Conclusion
Asterias is a highly invasive organism now currently established in Australia that has even
achieved pest status within its native range of Japan. Its wide range of tolerances and proven
adaptability in its invasive range within Tasmania and Victoria proves that an invasion in
New Zealand coastal waters will have serious consequences for environmental and cultural
values as well as economic production. As the highest introduction threat is from
contaminated ballast water and with the increasing globalisation and trading between world
markets and the associated rise in international trade and ship movement. There is a high risk
of an incursion although New Zealand biosecurity policies and procedures in conjunction
with international conventions may help keep the risk offshore.
Results of the mapping the environmental suitability for Asterias within New Zealand has
shown that while there is widespread depth, sufficient substrate and tidal dispersal suitability,
overall the temperature range is not optimal for reproduction or the dispersal of Asterias
larvae.
Adult Asterias however can persist within the current identified parameters, mostly in the
upper east coast and entire west coast of the North Island, the upper west coast and entire east
coast of the South Island. Survival in these and other areas are still within the lower survival
range for adult Asterias. Although as the predicted climate change model shows, this could
include the entire New Zealand coast in the future. To further enhance the validity of this
project, an analysis of wave action and creation of a map will need to be created and added to
the current overall suitability map.
An Asterias invasion would likely have significant effects on biological systems as it will
predate heavily on native bivalves, outcompete native species as well as causing alterations in

48. 48
habitats and community structure. It will further impact on cultural harvesting (kaimoana)
and aquaculture production.
New Zealand already has a number of endemic marine organisms that occur in small
populations and would be further impacted by an invasion of Asterias. Prevention measures
are the best risk management strategy New Zealand can employ to protect its marine
biological ecosystems, cultural heritage and continual economic activity.

49. 49
8. Recommendations
 New Zealand improves information dissemination regarding Asterias amurensis risk
assessments as they apply to the New Zealand environment.
 Management of this species and its related biosecurity risk should look keep the species
offshore to every practical extent.
 Prevention protocols, detection, eradication, containment and control should be
rigorously followed.
 Involvement of public, private and commercial stakeholders and Iwi should be
considered in minimising impacts if this species is introduced to ensure an integrated
management approach to eradication and control results.

50. 50
9. Acknowledgements
I would like to thank everyone who contributed to this project-
 Glenn Aguilar for the countless hours of GIS analysis help, critique and
recommendations for map improvements.
 Graham Jones and Nigel Adams for draft critiquing and helpful suggestions. Melvyn
Galbraith for allowing me to sit in on his student meetings.
 Lynne Lagiono-Lahina, Rowena Gilchrist and Janine Martin for all the weekend work
hours put in at the GIS computer labs and helping me select beautiful colours for my
maps.
 Finally the entire negotiated study students of 2010, for their encouragement and input
and just being awesome peoples.

51. 51
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11. Appendices
Appendix 1
Table 1: Temperature survival parameters.
Minimum Maximum
Adult temperature 0.0°C
No death after 10 days at
1 °C (Marsh 1993).
Adults lose weight below
4 deg C and above 20
deg C (Hatanaka &
Kosaka 1959; Park &
Kim 1985).
1.0- 25 °C ambient Japan
(Ino et al 1955).
Survived 12 hours in
laboratory at 4 °C
(Clapin 1996). In the
Mediterranean, found in
11 °C (Giangrande and
Petraroli 1994).
25.0 °C
Ino et al (1955) sampled A. amurensis from waters of 25 °C
in Tokyo Bay; Park & Kim (1985) reported death at 25 °C.
The following temperatures have been recorded for survival
of this species around the world:
0-25 °C ambient Japan (Ino et al 1955);
14-15 °C (Kume and Dan 1968 in Kasyanov et al 1998);
14 °C North/central Yellow Sea (Liao 1982); 6-14 °C
Hokkaido (Hawkes & Day, 1993); 6-14 °C Tonkin Bay
(Ino et al 1955 in Kasyanov et al 1998); 6.2-13.6 °C
Tokyo Bay and Sendai Bay (Hawkes & Day, 1993); 13 °C
(Hatanaka and Kosaka 1959); 8-11 °C Sendai Bay
(Hatanaka and Kosaka 1958 in Kasyanov et al 1998); 6-16
°C Ariake Sea (Nojima et al 1986); 9-13 °C optimum
(Davenport and McLoughlin 1993).
A. amurensis observed in the intertidal zone of the Derwent
River estuary during peak of summer (Feb 2000), no death
observed (S. Ling, pers. obs.). Mortality has been recorded
at the following temperatures: 25 °C (Park and Kim 1985);
upper limit 23 °C (Davenport and McLoughlin 1993).
Reproductive
temperature
5.0 °C Kim (1968) 23.0 °C Novikova (1978)

57. 57
Appendix 2
New Zealand Annual International Vessel Arrivals by port for the year 2006.
Port of first arrival. Annual international
vessel arrivals.
Whangarei 226
Auckland 1419
Tauranga 457
Gisborne 38
Taranaki 230
Napier 96
Wellington 99
Nelson 500
Picton 8
Lyttleton 105
Timaru 11
Dunedin 29
SouthPort 137
Westport 0