Competition, predation or herbivory and habitat degradation by marine pests Marine pests are any exotic marine species that may pose a threat to Australia's marine environment or industry if introduced, established or translocated. Large numbers of marine pests have been translocated into the Australian environment by a variety of means including through ships' ballast water and by attachment to ships' hulls, anchors and other structures (referred to as biofouling) (DEWHA, 2009c).
Australia has over 250 introduced marine species. Fortunately most remain relatively harmless but some crabs, mussels, seastars and seaweeds have become marine pests in various locations. The Northern Pacific seastar (Asterias amurensis) preys on native species depleting aquaculture and fishery operations, while the European fan worm (Sabella spallanzanii) forms a 'carpet' on the seabed, smothering native species for food and space and altering the marine habitat to suit itself (Marine Pests, 2009).
Three novel biota introduced to Australia, the northern Pacific seastar, wakame seaweed (Undaria pinnatifida), andEuropean/green shore crab (Carcinus maenas), were nominated by the IUCN as among 100 of the world’s most invasive species (Lowe et al., 2000). In Tasmania the arrival and establishment of the New Zealand screw shell (Maoricolpus roseus) and the marine clam (Corbula gibba), which now occur in high population densities on some-soft bottom sediments in southern Tasmania, threaten to irreversibly change the local species composition. This could further threaten the breeding and hence survival of the endangered Brachionichthys hirsutus (spotted handfish) (Hirst et al., 2007).
Other species with the potential to become invasive if introduced to Australia include the Chinese mitten crab (Eriocheir sinensis), Asian shore crab (Hemigrapsus sanguineus) and the jack-knife clam (Ensis directus (syn Ensis americanus)). These species impact on native species by altering habitat, causing bank erosion, and preying on and out-competing native species (Voigt, 1999, pp 31-35; Hopkins, 2001; Brousseau and Baglivo, 2005; Rudnick et al., 2005).
For this nominated group of novel biota that impact on biodiversity, two species—northern Pacific Seastarand New Zealand seastar (Patiriella regularis)—are provided as examples to further detail the impact of marine pests.
Northern Pacific seastar (Asterias amurensis) and New Zealand Seastar (Patiriella regularis) The northern Pacific Seastaris believed to have arrived in Tasmania early in the twentieth century in ship ballast from a ship from Korea or Japan (NIMPIS, 2002). It was first recorded in Port Phillip Bay in Victoria in the early 1990s (Parry et al., 2000). Northern Pacific Seastar is recognised by the IUCN and the Global Invasive Species Programme as among 100 of the world’s most invasive species (Lowe et al., 2000). The New Zealand seastar (Patiriella regularis) was probably introduced to Tasmania in a live oyster shipment from New Zealand in the early twentieth century (Dartnall, 1969; Waters and Roy, 2004).
The northern Pacific Seastar is a voracious predator, highly fecund, has a broad diet. The species has the potential to colonise water from Perth to Sydney to a depth of 100 m. This area includes World Heritage sites, Ramsar sites and protected marine areas (Dommisse and Hough, 2004).
Seastar larvae are easily sucked up in ballast water and can grow on boat hulls (Buttermore et al., 1994). They can also travel in oyster seed trays and mussel ropes, which are often moved between areas to maximise shellfish growth. Densities of the northern Pacific seastar in the Derwent estuary in Hobart have been as high as seven per square metre—among the highest in the world. Estimates suggest the population of northern Pacific seastars in Port Phillip Bay has reached 12 million in the two years since they were first observed, despite attempts to destroy the pests (Goggin, 1998).
These invasive seastars are very versatile and can out-compete native seastars and become dominant in the intertidal regions (NIMPIS, 2002). They out-compete the native species for food and habitat and also eat native species. The northern Pacific seastar feeds on a wide range of native marine animals and impacts on native shellfish populations that form a major part of the marine food chain by significantly reducing their numbers (Buttermore et al., 1994). In Australia, this invasive seastar has no native predators and flourishes due to rapid reproduction, which compounds the problem (NIMPIS, 2002).
Two native species of Tasmanian seastar listed as threatened under the EPBC Act are directly threatened by northern Pacific seastar. Patiriella vivipara (Tasmanian live-bearing seastar) is listed as vulnerable and Marginaster littoralis (Derwent River seastar) is listed as critically endangered. The northern Pacific seastar is known to prey upon the Tasmanian live-bearing seastar under controlled conditions (Prestedge, 1999) and along with the New Zealand seastar is reported to be the main threat (DEWHA, 2009d).
Similarly, the main threat to the Derwent River seastar is interspecific competition and displacement from introduced seastars, the New Zealand seastar and the northern Pacific seastar (DEWHA, 2009e). A potential threat from these introduced species is genetic swamping (hybridisation).
Materia (1994a) suggested that the Derwent River seastar may have been genetically swamped (hybridised) by the introduced New Zealand seastar. A microscopic examination that compared hybridised specimens with the Tasmanian museum specimens of the Derwent River seastar and the New Zealand seastar concluded that there was very little morphological difference between the original two species. No specimens that could be conclusively identified as the Derwent River seastar were found in a 1993 study, which may indicate the species had been subsumed by hybrids at that time, or that it had been excluded from its former range by morphological varieties of the New Zealand seastar (Materia, 1994b).
Summary of assessment: Invasive marine pests are the cause of decline in the population size and distribution of many threatened species and ecological communities, with local extinctions likely in the absence of effective control measures. In particular, northern Pacific seastar and New Zealand seastar are having an adverse impact on the Tasmanian live-bearing seastar and Derwent River seastar through direct competition, displacement and predation.
The Committee judges that this threatening process is adversely affecting many listed threatened species.
Mortality, habitat loss and degradation caused by pathogens Three pathogens that impact on Australian native species are currently listed as KTPs under the EPBC Act. They are ‘Psittacine Circoviral (Beak and Feather) Disease affecting endangered psittacine species’; ‘Dieback caused by the root-rot fungus (Phytophthora cinnamomi)’; and ‘Infection of amphibians with chytrid fungus resulting in chytridiomycosis.’ Two pathogens—Frog Chytrid Fungus and Phytophthora Root Rot—were nominated by the IUCN as among 100 of the world’s most invasive species (Lowe et al., 2000).
Psittacine Beak and Feather Disease (BFD) is a common and potentially deadly disease of parrots caused by a circovirus named Beak and Feather Disease Virus. The potential effects of the disease on parrot populations range from inconsequential to devastating, depending on environmental conditions and the general health of the parrots. The level of threat and distribution of the virus can be altered by the movements of common parrot species, for example the recent arrival of galahs and little corellas on Kangaroo Island, where the endangered glossy black-cockatoo lives and breeds in the same habitat (DEWHA, 2005e).
Australia’s native plants and ecological communities are threatened by the introduced soil-borne plant pathogen Phytophthora cinnamomi.Phytophthora die-back also poses a threat to many native bird species in south-western Australia, including various parrots and honeyeaters, such as the western spinebill (Acanthorhynchus superciliosus), due to the loss of nectar and seeds (e.g. from various Proteaceae) (DEWHA, 2005e). The endangered ecological community ‘Eastern Stirling Range Montane Heath and Thicket’ is adversely affected by Phytophthora die-back which is widespread in most occurrences of the community. The entire extent of the eastern Stirling Range has been infected by Phytophthora cinnamomi to some degree (Wills, 1993). The community contains a number of threatened EPBC Act listed species that are affected by Phytophthora die back including the endangered Andersonia axilliflora (giant Andersonia), Banksia montana (Stirling Range dryandra), Darwinia wittwerorum (Wittwer's mountain bell) and Lambertia fairallii (Fairalls honeysuckle). Another pathogen, myrtle rust (Uredo rangelii) was introduced into Australia in 2010 and poses a potentially serious threat to native species in the Myrtaceae family, including Callistemon spp., Melaleuca spp. and Eucalyptus spp. (Gollnow et al., 2010). Myrtle rust produces spores on infected plants and may result in the death of highly susceptible plants. Myrtle rust cannot be eradicated, as it produces large numbers of spores that are easily spread by wind, human activity and animals. The impact on native species is currently unclear however there is the potential for the pathogen to have a devastating effect on susceptible native species (DAFF, 2011).
Native fish are threatened by a number of pathogens including goldfish ulcer disease, Asian fish tapeworm and Epizootic Haematopoietic Necrosis Virus (EHNV). Escaped aquarium fish led to the spread of the goldfish ulcer disease that was introduced into Australia via infected goldfish and which eventually spread to native fish such as Bidyanus bidyanus (silver perch) (Corfield et al., 2008). Introduced fish are also the source of the Asian fish tapeworm (Bothriocephalus acheilognathi), which has caused substantial mortalities in Hypseleotris klungzingeri (western carp gudgeon) in the Canberra region (Dove et al., 1997). Introduced redfin perch are the main host for Australia’s first recorded finfish virus, the EHNV (Langdon, 1989; Whittington and Reddacliff, 1995; Reddacliff and Whittington, 1996; Whittington et al., 1996). Epizootic Haematopoietic Necrosis Virus is highly pathogenic for a number of native species, including Macquaria australasica (Macquarie perch), Galaxias olidus (mountain galaxias) and silver perch (Langdon, 1989).
In 1995, a mass mortality of Sardinops sagax (pilchards) occurred in Australia and spread east and west from the Great Australian Bight, to cover a distance of 6 000 km from Noosa in Queensland to Geraldton in Western Australia (Griffin et al., 1997). The exact cause of the mass mortality remains unknown however the best hypothesis is that an exotic pathogen, possibly herpes-type virus (Californian herpes), infected the pilchards. The source may have been from the release of ballast water or a contaminated frozen pilchard fed to caged tuna at Port Lincoln (Griffin et al., 1997, Ward et al., 2001 and references therein). Californian herpes reduced the Australian pilchard population to less than 30% of virgin biomass and also impacted on other species such as the eastern sea garfish which underwent a serious and inadequately explained decline at the same time as the sardines (Ward et al., 2001).
The critically endangered Galaxias truttaceus hesperius (western trout minnow), a Western Australian fresh water fish, has been found to be infected with the Pseudophyllidea cestode Ligula intestinalis, a cestode known to infect numerous freshwater fish species in the northern hemisphere (Morgan, 2003). This parasite impacts host reproductive output, swimming ability and leads to increased likelihood of predation (Morgan 2003). It is likely that the cestode was introduced into Western Australia in the 1950s and 1960 during the unsuccessful brown and rainbow trout releases or by avian host migrating from south-east (or south-west) Australia (Morgan 2003).
For this nominated group of novel biota that impact on biodiversity, chytrid fungus (Batrachochytrium dendrobatidis) is provided as one example to further detail the impact of pathogens.
Chytrid fungus(Batrachochytrium dendrobatidis) Chytridiomycosis is an infectious disease affecting amphibians worldwide (Fisher and Garner, 2007 and references there in) and was first identified in Australia in 1998 (DEWHA, 2002). It is not currently known whether the fungus is exotic or native to Australia and experts differ in their opinion on the likelihood of the fungus being a novel pathogen (Rachowicz et al. 2005; Fisher and Garner, 2007 and references there in). The disease has been recorded in four regions of Australia; east coast, south-west Western Australia; Adelaide; and central Kimberley. Chytridiomycosis is caused by the chytrid fungus, a highly virulent fungal pathogen of amphibians capable of causing sporadic deaths in some populations and 100% mortality in other populations.Surviving individuals are believed to be carriers. The inoculating dose is low, 100 zoospores able to cause clinical chytridiomycosis within four weeks. Some species appear highly susceptible to developing the disease, progressing to death, while other species appear less susceptible to disease manifestations (DEWHA, 2002). Many attributes of chytrid fungus and the disease in the wild are unknown, including survival of chytrid fungus in the absence of amphibian populations, methods of transmission and spread, and place/s and time of origin. Until recently the reasons for death of hosts was also unknown however it has been shown that pathophysiological changes including an ionic imbalance that causes cardiac arrest, result from infection (Voyles el al., 2009). There is no known treatment once chytrid fungus is contracted. It appears fungus zoospores are contracted through contact with water when released from infected frogs. Interaction between chytrid fungus and environmental factors, such as temperature and stress, vary the impact of the disease.
The Action Plan for Australian Frogs was completed in April 1997, before discovery of the disease. It states that dramatic declines in some Australian frog species have been reported since the 1980s, and, although some declines can be associated with changes to habitat, pollution and predation, for most species the cause of decline is unknown. Disease was speculated as a possible cause of decline in 10 species.
Over 30 listed threatened frog species are affected by chytrid fungus. Table 5 provides a list of frog species, listed as threatened under the EPBC Act, that are considered to be or have been adversely affected by chytrid fungus.
Table 5: EPBC Act listed species that list chytrid fungus as a threat.
Summary of assessment: Pathogens are the cause of decline in the population size and distribution of many threatened species and ecological communities, with local extinctions likely in the absence of effective control measures. In particular, chytrid fungus is having an adverse impact on many frog species by causing a serious decline in species abundance.
The Committee judges that this threatening process is adversely affecting many listed threatened species and ecological communities.
Conclusion for Criterion C: The Committee considers that the threatening process is eligible under this criterion as the process is adversely affecting population numbers and geographic distribution of many listed threatened species and threatened ecological communities, primarily through competition, predation, mortality and habitat degradation.
CONCLUSION: The threatening process meets s188(4)(a)(b) and (c) of the EPBC Act and is therefore eligible to be listed as a key threatening process.
Threat Abatement Plan
3.1 Degree of threat
The introduction and establishment of novel biota in Australia presents a significant risk to Australia’s environment and has resulted in adverse impacts on a number of native species from a variety of taxa, including many already listed as threatened under the EPBC Act. Novel biota are considered by biologists to have the second most destructive impact, after habitat destruction, on native species and ecological communities (Sanderlund et al., 1999, p 2; Coutts-Smith and Downey, 2006). Novel biota impact biodiversity through: predation by feral animals; soil erosion and water pollution; habitat loss; changes to hydrology, and; clogging and deoxygenation of waterways. Many native species such as the greater bilby and rufous bettong have undergone a decline in geographic distribution due to novel biota. The impacts of disease, hybridisation, competition and habitat degradation have also contributed to declines in some cases.