Biological pressures

Biological pressures are those arising from the proliferation of species beyond their natural densities or ranges. These pressures are usually the consequence of human activities that directly or indirectly facilitate the process; however, they also contain a degree of natural stochasticity and ecological opportunism that are beyond our control.

Biological pressures are typically very difficult to manage, due to their unpredictability, diffuse nature across large spatial scales and the complexity of the ecological systems in which occur. These pressures in the coastal zone include invasive species (terrestrial and aquatic), infectious diseases, mass die-offs, harmful algal blooms and jellyfish blooms. There is debate among scientists about whether some of these pressures, such as jellyfish blooms, are nuisance events driven by human influences, or simply natural events operating at timescales beyond our understanding.

Assessment Biological pressures
2021 Assessment graphic showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.
Somewhat adequate confidence
Indigenous assessment
2021 Assessment graphic for an assessment conducted by Indigenous community members, showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.

Invasive species are an ongoing challenge in coastal environments, and are considered very high impact in terrestrial environments and high impact in aquatic environments. Invasive species can have devastating ecological and economic consequences, particularly in areas with sensitive ecosystems, such as islands. Both terrestrial and aquatic invasions are getting words, and the management of both remains a difficult problem. Diseases and blooms are considered relatively low-impact and stable pressures.
The Indigenous assessments for the state of biological pressures found 1 pressure has a low impact, and the trend is stable.
While terrestrial invasive species are problematic for many local government areas Australia-wide (see Approach), other biological pressures are felt in fewer areas.
Related to United Nations Sustainable Development Goal target 15.8

Assessment Aquatic invasive species
2021 Assessment graphic showing that pressures are high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The situation is deteriorating.
Somewhat adequate confidence
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The trend was unclear.

Aquatic invasive species are a pervasive and significant threat that is difficult to manage. Management is improving with new technologies and legislation, but national surveillance is lacking.

Assessment Terrestrial invasive species
2021 Assessment graphic showing that pressures are very high, meaning they strongly degrade the state of the environment, over a large extent and with a high degree of severity. The situation is deteriorating.
Adequate confidence

Invasive species are a pervasive threat in coastal Australia. Many invasions are accelerating, but management approaches are also evolving rapidly.
The Indigenous assessment for some local areas was low, with a stable trend.

Assessment Infectious diseases and mass die-offs
2021 Assessment graphic showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.
Limited confidence
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The trend was unclear.

Major disease outbreaks, such as white spot disease (Queensland) and Pacific oyster mortality syndrome (New South Wales, Tasmania and South Australia), have occurred.

Assessment Harmful algal blooms
2021 Assessment graphic showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.
Somewhat adequate confidence
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The situation was improving.

Different harmful algal blooms occur in different regions and show different trends; there has been no strong overall trend in frequency of blooms.

Assessment Jellyfish blooms
2021 Assessment graphic showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The trend is unclear.
Low confidence
Assessment graphic from 2011 or 2016 showing that pressures were low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation was stable.

Very few long-term datasets are available to monitor trends in jellyfish blooms, and no new datasets have emerged since 2016.

Aquatic invasive species

More than 250 marine species have been introduced into Australia (DAWE 2021b); however, this is likely to be an underestimate due to many cryptic (biologically similar) species not having been detected or identified. Newly detected non-native marine species include the colonial sea squirt (Didemnum perlucidum) in Western Australia, the Northern Territory and Queensland; the black scar oyster (Magallana bilineata) in Queensland; the soft-shelled clam (Mya japonica) in Tasmania; and the Asian shore crab (Hemigrapsus sanguineus) in Victoria.

Management activities in Australia are primarily focused on preventing the introduction of new pests through ballast water and biofouling, and developing a national surveillance network.

All ships entering Australian waters are required under the Biosecurity Act 2015 to manage their ballast water, which aligns with the International Maritime Organization (IMO) Ballast Water Management Convention 2009. This can be achieved using onboard ballast water management systems that remove or kill viable organisms before discharge, or ballast water can be exchanged in designated offshore areas prior to arrival in Australian waters.

At the international level, biofouling is currently managed through a code of practice; however, Australia is developing biofouling regulations consistent with the direction of the IMO. The levels of regulation placed on vessels differ between states. Several states and territories require vessels and some industries to undertake regular biofouling inspections of their infrastructure. Western Australia has also developed a vessel biofouling risk assessment tool (Vessel-Check) to identify high-risk vessels. This risk tool is now being implemented in Victoria and New South Wales. The Australian Government, working with close international jurisdictions, is currently developing guidelines for in-water cleaning of vessel hulls, to help manage the risk of the unintentional release of viable propagules during the cleaning process (Sherman et al. 2020).

Several activities are undertaken by federal and state agencies and several industries to manage and reduce the risk of new species introductions and the spread of established pest species. However, further increases in these activities are needed across Australia to establish an effective surveillance network that would provide the early detection needed to implement emergency management responses. Several states and territories have, or are developing, surveillance programs, however there is a need to implement standardised and long-term active surveillance across all states and territories and to expand existing programs in collaboration with key industries and stakeholders.

A key component of the MarinePestPlan 2018–2023 is the development of a national marine pest surveillance strategy and surveillance work plan. The main aim of surveillance is to provide early detection and management of introduced species. To facilitate early detection, robust, reliable, cost-effective and practical surveillance and detection techniques must be available. Active or planned surveillance programs for priority areas (e.g. ports, harbours and high-value environmental sites) currently operate in the Northern Territory and several states, including Western Australia (SWASP), the Northern Territory, Queensland (Q-SEAS) and Victoria. These programs include the use of traditional visual (in-water and shoreline) surveillance and settlement plate arrays, and are increasingly using molecular diagnostic tools. Many state agencies and local community groups also contribute to surveillance activities of targeted areas, which provides a cost-effective approach for detecting recently introduced species and monitoring the spread of established pest species. The importance of passive surveillance is highlighted by the detection of new incursions of new and established pest species, including the northern Pacific seastar (Asterias amurensis), Japanese kelp (Undaria pinnatifida), Pacific oyster (Crassostrea gigas) and the Asian shore crab (Hemigrapsus sanguineus).

Management of some established pests is continuing (e.g. Japanese kelp, northern Pacific seastar, Pacific oyster), but only at targeted locations and often by community groups. Tools that allow for containment and eradication in the active management of most marine pest species are lacking. Current approaches are typically limited to hand removal or wrapping (wrapping of a vessel or structure in plastic sheets or canvas sleeves to suffocate biofouling); these approaches can only be applied to relatively small, targeted areas and therefore often have limited effectiveness. Early detection, location and removal technologies are needed to enable more-effective on-ground management when new pest species or incursions are detected.

Terrestrial invasive species

Invasive plants, animals and microbes are a pervasive threat in coastal environments, affecting all ecosystems from subantarctic islands to the tropics. Introduced species have direct negative impacts on native species, including predation (e.g. by foxes, cats and rats), pathogenic effects (e.g. myrtle rust, phytophthora) or competitive displacement of native species (e.g. many weeds of national significance). Both the invasive species themselves, and the approaches we use to manage them, are evolving rapidly. This is not a battle we can win in the short term, but our efforts are having clear economic and biodiversity benefits.

Major impacts of terrestrial invasive species on coastal ecosystems include:

  • feral pigs preying on marine turtle eggs (Whytlaw et al. 2013, Nordberg et al. 2019) and degrading coastal wetlands
  • feral herbivores, including pigs, buffalo and cattle, degrading coastal wetlands (Sloane et al. 2018, Sloane et al. 2021)
  • invasive rodents, foxes and cats preying on seabird colonies (Jones et al. 2008)
  • spread of serious invasive weeds such as bitou bush, marram grass, sea spurge and Singapore daisy. For example, 500 weed species have been recorded in the South Australian coastal zone, equating to more than 30% of the total coastal flora (Sandercock & Schmucker 2006). A 2012 report estimated $30 million a year is spent managing coastal weeds in South Australia, and noted lack of management except for a few declared weeds and weeds of national significance (Cousens et al. 2012).

Some of the most serious invasive species (e.g. foxes, bitou bush) can invade natural, unmodified ecosystems. However, most biological invasions are facilitated by anthropogenic (human-caused) factors such as changes in nutrient or water availability, changed disturbance regimes, structures, and climate change (Geedicke et al. 2018, Abbott et al. 2020).

Several factors are contributing to increases in the scale and impact of biological invasions in Australia:

Historically, managers have focused on removing or reducing introduced populations, through chemical treatments, culling programs and physical removal. These approaches continue to be important tools for invasive species management, and the return on investment in these programs is generally excellent (e.g. the starling control program in Western Australia has a cost–benefit ratio of 1:6 (Campbell et al. 2016)). Pesticides have a role in controlling invasive species, despite also having direct negative impacts to the environment. However, approaches that shift the emphasis away from removing invaders and instead work to restore natural conditions to invaded sites have been showing substantial promise. For example, removing artificial structures that impede tidal movement has led to a massive reduction in invasive plant cover in northern Queensland (Abbott et al. 2020).

Technological advances are making eradication of invasive species from offshore islands increasingly feasible, as shown by programs on Lord Howe Island and Dirk Hartog Island (Heriot et al. 2019), and native species are showing very positive responses to these eradications (Comer et al. 2020).

Another very positive trend in invasive species management is that the social and environmental benefits of increased engagement with Indigenous land managers are much more widely appreciated now than they were in 2016 (Waltham et al. 2018, Sloane et al. 2019) (see the Indigenous chapter). Community groups also contribute to invasive species management; for example, Tasmanian volunteers removed the majority of sea spurge from Tasmania’s World Heritage coastline.

Our understanding of both the impacts of introduced species on native species and best management practice are becoming more nuanced. We now know that even serious invaders such as African boxthorn and lantana can create habitat and provide fruit resources for native fauna (Carlos et al. 2017, Wright et al. 2019). Thus, removing invaders can sometimes have negative impacts on native ecosystems (Wright et al. 2019). This complexity, combined with the impossibility of eradicating some of the more widespread invasive species, has led researchers to suggest that managers might sometimes have to accept novel ecosystems that contain a mixture of native and introduced species (Hobbs et al. 2013).

Case Study Rapid evolution in introduced species in Australia

Evolution and speciation were historically thought of as processes that happen over geological time. However, it has recently become clear that plant and animal species can undergo substantial evolutionary change within just a few years or decades. Introduced species are particularly likely to undergo rapid evolutionary change, as they experience different environmental conditions and interact with a suite of different species when they arrive in a new country. In fact, a study of 23 plant species introduced to New South Wales in the past 150 years or so found that 70% had undergone significant morphological change since their arrival (Buswell et al. 2011).

Rapid evolution can allow invasive species to spread more effectively in their new ranges. For example, cane toads in Australia have evolved longer legs and hop in straighter lines, which results in much greater dispersal speeds and an exponential increase in the rate of range expansion (Phillips et al. 2006).

Rapid evolution can also allow invasive species to change their morphology, physiology and reproductive biology to become better adapted to survive in Australian conditions. An example of this is Arctotheca populifolia, a beach daisy introduced to Australia from South Africa in the 1930s (Figure 32). A. populifolia has changed its growth form and leaf shape (Brandenburger et al. 2019b), photosynthetic rate, and water use efficiency (Brandenburger et al. 2019a) to better suit the windier, drier conditions it encounters in Australia. It has also developed self-compatibility, which allows it to produce seeds without assistance from pollinators.

Rapid evolution will likely lead to an increase in both geographic scope and impact of many plant and animal invaders over the coming decades.

Figure 32 Source and Australian plants of Arctotheca populifolia

Photo: Claire Brandenburger

Infectious diseases and mass die-offs

Exotic pathogens are introduced to our marine environment through various pathways, such as through imported seafood, vessel biofouling or ballast water discharge (Deveney 2019, Georgiades et al. 2021). Between 2016 and 2021, significant fish and other marine animal mortalities due to infectious disease have been regularly reported from most jurisdictions (Roberts et al. 2019, Readfern 2020, Young et al. 2020).

Recent analyses show that shipping patterns, shipping volumes and trade routes all contributed to an increased likelihood of translocation of marine organisms that carry internationally significant mollusc pathogens, such as Bonamia and Perkinsus parasites and ostreid herpesvirus-1 microvariant (OsHV-1 µvar) (Georgiades et al. 2021). Pacific oyster mortality syndrome (POMS) caused by OsHV-1 µvar has had an extensive impact on farmed Pacific oyster populations in New South Wales (2010–13) and Tasmania (2016) (Deveney 2019), and feral Pacific oyster populations in South Australia (2018–20) (PIRSA 2020).

To manage disease risks, Australia has a longstanding national reporting system for aquatic animal diseases of significance to fisheries, aquaculture and the environment (DAWE 2020c). All states and territories have agreed to report the diseases that are listed on Australia’s National List of Reportable Diseases of Aquatic Animals (National Disease List). Legislation allows all jurisdictions to obtain information on any new aquatic animal diseases, including significant die-offs of wild aquatic animals. As recommended by the 2017 Priorities for Australia’s biosecurity system report, the National Priority List of Exotic Environmental Pests, Weeds and Diseases (Environmental Priority List) was released in November 2020 (DAWE 2020b). The National Disease List covers all aquatic animal diseases on the Environmental Priority List, as management of aquatic animal diseases considers environmental impacts. The establishment of the Environmental Priority List strengthens Australia’s environmental biosecurity through a national approach to improving preparedness and response activities, and guides further research priorities.

Impacts caused by aquatic animal diseases can be increased by environmental stressors, such as marine water heatwaves, sudden temperature changes and contamination by various pollutants. For example, extreme weather events were implicated as a stressor contributing to mass mortalities, caused by Streptococcus iniae, of approximately 20,000 marine fish from more than 35 species north of Broome, Western Australia in March 2016 (Young et al. 2020). A sudden drop in water temperatures in the Moreton Bay region in November 2016 was considered as a risk factor for the expression of white spot disease on prawn farms on the Logan River in Queensland (Diggles 2017).

While Australia’s marine ecosystems will continue to face pressures due to various environmental stressors and increased pathways of pathogen introduction, Australia can reduce potential impacts on marine environments through a greater understanding of biosecurity risks. Our knowledge of marine diseases is almost entirely confined to aquaculture, and diseases in wild populations are a major research gap. Wild populations are subject to different pressures than aquaculture populations, and can be genetically and phenotypically different. Patterns of disease outbreaks can therefore be quite different between wild and aquaculture populations in the same waterway.

While the concerns related to aquaculture vary between states based on the species cultured and culture practices, biosecurity is a real concern everywhere. There have been 2 serious biosecurity issues in recent years:

  • The outbreak of POMS in Tasmania in 2016 decimated the Pacific oyster industry in that state and significantly affected production elsewhere around Australia. For example, while farmed oysters in South Australia were classified as POMS free, the South Australian oyster industry was heavily reliant on spat grown in Tasmania, and their production was markedly affected by the POMS outbreak.
  • White spot disease, a highly contagious viral infection that causes high levels of mortality in prawns and crabs, was detected in south-eastern Queensland in 2016. It caused a significant financial impact on prawn farms and wild fishers in the region (Ridge Partners 2017), and there was no production from farms in this region for a couple of years. Some farms have returned to production, but the virus has established in some populations of wild crustaceans within the Queensland Movement Regulated Area. Movement and fishing restrictions and ongoing surveillance are in place.

While strategies have been developed to manage both these health issues, biosecurity measures are important in aquaculture planning, including detailed prerequisites for translocation of stock and equipment, targeted monitoring and testing, and recommended spatial distancing between leases. However, the biosecurity consequences of inadvertent translocation of pest species, and in particular feral Pacific oysters (Crassostrea gigas), remain a significant concern in several states (Hutchings 2018, Schaefer et al. 2020).

Harmful algal blooms

Harmful algal blooms (HABs) are multifaceted, comprising a wide range of phenomena caused by some 150 different marine organisms, most of which are phytoplankton. HABs can have negative socio-economic impacts on humans and the marine environment, including:

  • water discolourations, scum or foam; for example, Noctiluca scintillans red tides closing beaches
  • biotoxin accumulation in seafood above levels considered safe for human consumption; for example, paralytic shellfish toxins from Alexandrium pacificum in New South Wales in 2016 and the Swan and Canning rivers (Western Australia) in 2019–2020, and Alexandrium catenella in Tasmania in 2016 and 2017 where toxins in mussels were 200 times above the regulatory level; both cases resulted in shellfish or other invertebrate (abalone, rock lobster) harvesting bans
  • other events where humans, animals or other organisms are negatively affected by algae; for example, ciguatera poisoning from recreational fish caught in northern New South Wales in 2016.

Some HABs are known about from Australia’s history (Ajani et al. 2001). For example, fish kills and anoxia are known from Sydney Harbour since 1899, Noctiluca was present in Sydney Harbour in 1860, ciguatera has been recorded from the Great Barrier Reef since 1934, and Alexandrium spp. are known from Tasmania for at least 8,000 years (sedimentary DNA studies).

There is concern that many HAB species are becoming more problematic with climate change. This is because most HABs are dinoflagellates, which benefit when waters are more stratified, a likely consequence of climate warming. This effect could be exacerbated by eutrophication (excess nutrients) and transport of HABs into new regions via ballast water. However, there is currently no statistical evidence that HABs are increasing in frequency or global distribution; rather, societal impacts are increasing because of enhanced use and hence increased monitoring of coastal waters for aquaculture (Hallegraeff et al. 2021) (see Aquaculture).

Individual HAB species respond to different environmental drivers, including water column stratification (e.g. changes in temperature and salinity), nutrients (including micronutrients from land run-off), dispersal (e.g. currents and local oceanography) and ecosystem disturbance (species range extensions, increased or decreased grazing pressure, ballast water). Some aquaculture, such as the expanding salmon farm industry in Tasmania, also drives HAB impacts. Overall, ciguatera remains the most significant HAB problem in Australia in terms of its impact on human health (1,400 reported human illnesses and 2 fatalities between 1965 and 2019). However, neither the causative benthic dinoflagellates nor their toxins in seafood are currently routinely monitored.

There have been several HAB events in Australian waters in 2016–20 (Figure 33). These include relatively benign events such as multiple large Noctiluca blooms in 2020 in Eaglehawk Neck (Tasmania), Jervis Bay (New South Wales) and the Brisbane River estuary (Queensland). Blooms of Alexandrium that can cause paralytic shellfish poisoning have also been detected in Tasmania, New South Wales and Western Australia (Barua et al. 2020).

Figure 33 Map of iconic harmful algal bloom events around Australian coasts, 2016–20

Changes in HABs

Climate change drives the distribution and abundance of species and thus we may see the emergence of new HAB problems in areas where they did not previously occur. Increasing use of coastal waters for recreation and aquaculture may also drive the emergence of new HAB impacts.

Data are patchy, but we know that Noctiluca scintillans is expanding its range in response to climate change and other factors (McLeod et al. 2012), and there is a small amount of evidence for increasing abundance of Noctiluca in the south-east bioregion in recent years. Based on data from the Australian Ocean Data Network, the New South Wales shellfish industry and Microalgal Services, other HAB species appear and disappear (e.g. there were negligible problems with paralytic shellfish toxins in Tasmania in 2018–20) or are stable. Human ciguatera poisonings – globally concentrated in tropical regions – have long been known from Queensland waters, and are increasingly occurring in northern New South Wales, although it is not yet clear whether this is due to range expansion of the causative benthic dinoflagellates, or migration of fish species, or both (Farrell et al. 2016). HAB species and their toxins are poorly monitored in most areas.

No statistically significant trend of all HABs in all regions has emerged, nor is to be expected, because of the complexity of marine systems. Intensified HAB monitoring efforts, driven by the ever-increasing need to exploit coastal marine resources, acts as a natural multiplier that may lead to a reported increase in impacts of HABs on human society, independent of their actual trend.

HAB monitoring and research

Collaboration between industry, researchers and regulators, as well as sharing of data between parties, will be critical to improving management of our marine resources for both the protection of human health, and sustainability of the farmed and wild harvest sectors.

The establishment of ever-improving HAB databases such as Harmful Algae Event Database and the Integrated Marine Observing System Australian phytoplankton database (Davies et al. 2016) are improving bloom understanding and predictability. Australia is part of a global process, sponsored by the Intergovernmental Oceanographic Commission of UNESCO, which is producing a global HAB status report. The report includes a global overview for the period 1985–2018, as well as a comprehensive regional summary for Australia and New Zealand (Hallegraeff et al. 2021).

However, climate change is causing the emergence of new problems in poorly monitored areas. HABs causing ciguatera poisoning via consumption of coral reef fish are not monitored today in Australia and HABs impacting the finfish farm industries are poorly monitored. Little is known about the potential involvement of HABs in broader marine mortalities such as whale strandings. The food-web impact of expanding frequency, intensity and distribution of strongly phagotrophic red Noctiluca blooms in Australian waters, if similar to the impact of green Noctiluca in the Arabian Sea, remains to be fully understood.

Jellyfish blooms

Jellyfish (defined as cnidarian medusae and ctenophores) are often a conspicuous presence in Australia’s coastal waters. Jellyfish are generally considered to thrive in areas of anthropogenic disturbance (Richardson et al. 2009), but evidence for this is limited (Pitt et al. 2018). Although some species of jellyfish have increased in abundance in some of the world’s coastal regions, they have declined in others (Condon et al. 2013).

Assessing trends in Australia’s jellyfish populations is challenging due to the scarcity of long-term datasets. The Queensland Government has recorded the presence or absence of the scyphozoan medusa Catostylus mosaicus since 1998 in estuaries extending from far north Queensland (Daintree River) to the New South Wales border. Analysis of the data for Moreton Bay revealed no net change in populations, but identified that populations tend to oscillate in 5–7-year cycles (Joensen 2014). Quantitative trawl surveys of C. mosaicus in Port Phillip Bay (Victoria) from 1990 to 2010 seemed to show that populations had increased, but anecdotal observations after the monitoring program concluded suggested populations subsequently declined (G Parry, Victorian Department of Primary Industries, pers. comm., 2010).

State-based surf lifesaving organisations record stings of beach users by bluebottles (Physalia physalis), but data have not been formally analysed. Stings by dangerous cubozoan medusae, which include the predominantly tropical irukandji species and the box jellyfish (Chironex fleckeri) are also recorded (Gershwin et al. 2014). Anecdotally, envenomation by irukandji appears to now occur consistently at K’gari/Fraser Island in Queensland and at Ningaloo Reef in Western Australia. This could indicate a southern range expansion of these species, or in the case of Ningaloo, reflect a high level of visitation and immersion for tourism.

However, considerable caution needs to be applied when using sting data to infer jellyfish population trends. The likelihood of encountering jellyfish depends on the number of people available to be stung, so changes in tourism and beach usage could therefore lead to erroneous interpretations of jellyfish population trends. There is also increasing evidence of highly localised populations of deadly jellyfish, which needs to be considered when estimating levels of risk to swimmers (Schlaefer et al. 2018).

New tools have recently emerged to monitor jellyfish populations, including remote-sensing approaches such as drones (Rowley et al. 2020) and cameras attached to piers (Llewellyn et al. 2016) and underwater (Schlaefer et al. 2020), and molecular techniques such as environmental DNA. These emerging technologies should make monitoring of jellyfish populations more cost-effective and improve understanding of trends across time.