As global temperatures continue to change because of greenhouse gas emissions, ecosystems everywhere will be impacted. One of the impacts that is already being seen is the proliferation of invasive species in aquatic environments. In this article we will look at some of the connections between climate change and invasive species.
What are Invasive Alien Species (IAS)?
Non-native, alien, exotic, foreign, introduced, and non-indigenous species are organisms occurring outside their natural distributional range caused by vectors—the transfer mechanism responsible for their introduction and spread. For alien species these vectors are primarily a result of anthropogenic (human) activities (Falk-Petersen et al. 2006) that directly and indirectly and deliberately or accidentally encourage the dispersal—movement of propagules from one area to another—of alien species (Carlton 2001).
Of the many species introduced outside of their native range, only a fraction establishes permanently in their new environment (Sakai et al. 2001; Colautti and MacIsaac 2004). It is when the population densities of these alien species are high and successfully disperse over wider ranges that they become a significant threat to native biota, biodiversity, ecosystem properties, ecosystem processes, and community structure, the economy, and human health (Ruiz et al. 2000; Lodge et al. 2006; Simberloff et al. 2013; Levine et al. 2003; Lodge et al. 2006) they are consequently termed invasive (alien) species (IAS) (Sakai et al. 2001; Colautti and MacIsaac 2004). Invasive species typically are successful and abundant, where many native species are rare as many have characteristics that differ from non-invasive species. Many invasive species have broad climatic tolerances and large geographic ranges (Rejmanek 1995) making them potentially less susceptible to the adverse impacts of climate change compared to native species. Alien species also have characteristics that facilitate rapid range shifts (e.g., low seed mass and short time to maturity) (Rejmanek & Richardson 1996).
In Canada there are many aquatic invasive species are already established, including European Green Crab, Vase Tunicate, and Zebra and Quagga mussels. However, others threaten invading, like the Asian carps or are native to some parts of Canada but invasive in others such as Sea Lamprey and Smallmouth Bass.
What is the role of climate change on invasive species?
Climate change will challenge the very definition of invasive alien species because some taxa that were previously invasive may diminish in impact; previously non-invasive species, may become invasive; and many native species will shift their geographic distributions for survival, moving into areas where they were previously absent. Despite these uncertainties climate change is anticipated to lead to aquatic invasions through a variety of mechanisms (Poff et al. 2002):
Increased water temperatures have been observed to promote the establishment of alien microalgae species. Among these alien microalgae, some have impacted human health. For example, in the Ligurian sea, the IAS, Ostreopsis cf. ovata has bloomed and has caused respiratory illness to tourists upon exposure (Brescianini et al. 2006; Durando et al. 2007; Vila et al. 2016). Apart from the human health implications, this IAS also demonstrates how the climate change-IAS nexus may adversely impact tourism, commerce, and recreation.
Natural saline aquatic systems will undoubtedly increase in salinity; however, whether this will necessarily allow marine species to penetrate inland waters is unknown (Rahel and Olden 2008).
The alteration of human transport patterns from climate change may influence IAS because of new or increased transport between a source and target region or because of enhanced survivorship of propagules during transport (Hellmann et al., 2008). For example, the loss of Arctic Sea ice, a viable Northwest Passage, from climate change will substantially reduce travel time for some ships and the survivorship of organisms in ballast water or on ship hulls (Pyke et al. 2008).
Extreme weather (e.g., storm surges) or altered circulation patterns could enhance dispersal of some invasive species (Hellmann et al., 2008). For example, as hurricanes sometimes carry birds, marine larvae and insects, considerable distances from their native range (Green & Figuerola 2005), there increased frequency or intensity under climate change (IPCC 2007) may increase the dispersal of IAS.
The Vectors and Pathways for Marine Alien Species
Ballast water
Ballast water is fresh or saltwater stored in ships' ballast tanks and cargo holds for stability and maneuverability throughout a voyage when ships are not carrying cargo, are not carrying heavy enough cargo, or when extra stability is necessary due to severe seas. An expanding global human population and economy stimulate the flow of products across the oceans, bringing invasive organisms with them via ballast water and adhering to ship hulls. Approximately 10,000 species are transferred across different biogeographic zones in any given 24-hour period (Geburzi & McCarthy, 2018). According to Wonham et al. (2001), over 98% of organisms collected in ballast water at the start of vessel voyages are not discovered at the end of voyages, and malnutrition, predation, poor light availability, and changing temperature are likely causes of death during transport. Climate change could affect these probabilities. In other circumstances, humans purposefully assist many alien species during the transport and colonization phases of invasion (Hellman et al., 2008).
Fouling communities
Fouling communities consist of sessile (permanently attached) species that colonize human-made structures including ship hulls that allows for their transportation between ports (Ruiz et al. 1997; Gollasch 2002; Geburzi & McCarthy, 2018), mariculture farms, and seawater pipelines, as well as natural hard substrata (Harris and Tyrrell 2001, Valentine et al. 2007). For example, the study of Sorte et al. (2010) determined that seven alien species (of the eleven sessile invertebrate species) covered 71% of the dock fouling community and 80% of the occupied space. The increasing dominance of invasive alien fouling species could potentially influence ecosystem and economic impacts of the community by increasing the demand for fouling control practices and leading to changes in filtering rates and water clarity (Wilkinson et al. 1996), mobile (e.g., fish) species abundances and diversity (Clynick et al. 2007), and competition with farmed shellfish (McKindsey et al. 2007).
Aquaculture
Aquaculture is another vector for marine IAS, as supported by the increasing number of introductions in tandem with the global expansion of industry (Naylor et al. 2001). An example of aquacultures’ contribution to the spread of IAS is the Pacific oyster Magallana gigas. Like, other planktonic larval organisms that are prone to “spill over” from their culture sites into surrounding environments, M. gigas—that was initially thought to be incapable of reproducing in the cold temperature of the North Sea—established along the southeastern shore of the European North Sea thanks to a series of warm summers. M. gigas demonstrates how the cumulative effect of anthropogenic activities, environmental change and species traits can lead to a successful invasion (Diederich et al. 2005; Smaal et al. 2009).
Marine litter & Pollution
While marine litter is a problem mostly discussed in terms of the hazardous effects of microplastic accumulation, larger pieces of litter can potentially serve as habitat for alien fouling organisms. For example, recent studies detected a variety of species, in which a significant proportion were marine IAS. (Barnes and Milner 2005; Gregory 2009; Gil and Pfaller 2016).
Apart from marine litter, water pollution and eutrophication can disrupt marine ecosystems and communities, making them more receptive to invasions (Reise et al. 2006; Briggs 2007). For example, experimental studies have revealed that IAS have a higher stress tolerance (i.e., toward water pollution) compared to native marine species and their communities (e.g., Piola and Johnston 2008; Crooks et al. 2010; Lenz et al. 2011).
Marine Infrastructure
Anthropogenic habitat changes and disturbances can increase resource availability for IAS. For example, the construction of harbors and coastal defense structures (e.g., groins or seawalls) adds artificial rocky habitats that are often rapidly colonized by alien species as the native species are less adapted to the conditions (Mineur et al. 2012).
Management of IAS
IAS are managed in fundamentally differently ways than native species (i.e. control vs conservation) with invasive species managed to prevent their establishment and spread. The best method for managing IAS is prevention, however when prevention is no longer an option, mechanical (physical removal), chemical (e.g. herbicides and pesticides), and biological (predators, parasites, and pathogens) mechanisms can be used alongside restoration. The efficacy of these tools can be influenced by climate change. For example, the range of water hyacinth (E. crassipes) and water lettuce (Pistia stratiotes) is limited by cold, hard freezes, or ice cover (Owens et al. 2004); however the potential for warmer winter temperatures from climate change would allow these plants to overwinter causing mechanical control as a management tool to be more resource intensive and expensive. Likewise, if climate change enhances some IAS, the resulting increased use of herbicides and pesticides may amplify negative effects on non-target native organisms (Howe et al. 2004; Cauble & Wagner 2005).
Final Thoughts
A small corpus of work investigates how climate change may affect invasive species impacts through changes in range, abundance, and per capita effect. Few studies have investigated whether invasive species will become more prevalent because of climate change (Hellmann et al., 2008). While a rapidly rising body of literature in recent years has helped to narrow the gap (Grosholz and Ruiz 1996; Ruiz et al. 2000; Chan and Briski 2017). Marine environments are among the most heavily invaded in the world yet have been underrepresented in studies compared to terrestrial and lake systems (Geburzi & McCarthy, 2018). This could be because of the vastness and open character of the marine environment which increases the difficulty to identify, investigate, and control marine invasions thus necessitating greater efforts and at higher costs (Geburzi & McCarthy, 2018).
One of the most comprehensive models for predicting the fate of marine invasions is that of Cheung et al (2009) whereby the distributional ranges of 1,066 marine fish and invertebrates for 2050 were considered in a bioclimate envelope model. The model predicted that there would be a high species turnover rate of 60% attributed to invasions and extinctions by the mid-21st century in high latitude regions of the Arctic and Southern Ocean.
The potential implications of marine IAS and their response from and to climate change ecosystem warrants the need to improve our understanding on the relationship between marine IAS and climate change for biodiversity, ecosystem properties, ecosystem processes, and community structure, the economy, and human health. As such, future studies should consider marine IAS and climate change together to carefully predict climatic conditions of the future to help hypothesize marine invasions and develop management approaches and preventative measures.
We can all do our part to help prevent the spread of species in our waters by following a few simple guidelines. these can be found at the government of Canada’s website: https://www.dfo-mpo.gc.ca/species-especes/ais-eae/prevention/index-eng.html.
Don’t release live animals, pets or food into the environment, ensure that boating equipment is properly managed when moving between bodies of water, and don’t move water or living organisms from one body of water to another. Although climate change is recognized as having an influence on invasive species, its important that we do not contribute to the problem.
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Contributors
Researchers
Katarina Duke
Authors
Katarina Duke
Mauro Aiello, Ph.D.
Lark Scientific Financial Support
Axel Doerwald
Graphics
Adri Poggetti