Tunicate colony of Didemnum vexillum Tunicate colony of Didemnum vexillum

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Invasive species and the climate crisis

What are the links between climate change and marine invasive non-native species (INNS), and how can we manage the threat of INNS?

The Millennium Ecosystem Assessment (MEA, 2005) identified non-native species and climate change to be the greatest anthropogenic impacts to biodiversity.

Non-native species (NNS) are defined as those species that have been intentionally or unintentionally introduced outside their natural range as a consequence of human activity.

Invasive non-native Species (INNS) are those species which cause unwanted environmental (alteration of habitats and ecosystem functioning), economic (changes to industry or processes), or social (threat to public health) impacts.

In the UK it is estimated that over 1,795 terrestrial, freshwater and marine NNS, from as far away as Asia, North America and the Pacific, have already become established. Approximately 15% are classified as invasive, with an estimated cost to the UK of £2bn per annum.

In addition, climate change has the potential to increase the threat caused by marine INNS by creating conditions which enable them to survive and thrive in UK waters.

Evidence suggests that NNS are generally more tolerant to environmental change than native species, so climate change may lead to competitive dominance of NNS due to native species extinctions. As such, more NNS could become established, currently benign NNS could become invasive, and native species may become locally extinct.

In the North Atlantic, changes to climate and related extreme weather events have already led to the introduction and migration of NNS. Regional climate models predict that the current trend of warming will continue throughout the 21st century, providing further opportunities for NNS to establish themselves.

How does climate change facilitate the spread of INNS?

A widespread expectation of climate change is that alterations in global temperature and precipitation regimes will favour an increase in the number, distribution and impact of non-native species.

Increasing evidence is now available to show that climate change has led to the northwards range expansion of a number of INNS in the UK and Ireland, such as the Asian club tunicate Styela clava and the Pacific oyster Crassostrea gigas (Cottier-Cook et al., 2013).

Indeed, climate change could influence the spread of NNS in Great Britain in at least seven ways:

  1. Introduction of new INNS: New species may be introduced either accidentally or deliberately as a result of changes in trade, tourism, immigration, or as a result of greater dispersal opportunities due to changes in wind and ocean currents attributable to a changing climate.
  2. Northward range expansion: Increasing temperatures can facilitate to northward shift in INNS range into areas which may not have been previously suitable for the species. Many INNS have the ability to expand rapidly to higher latitudes and altitudes as the climate warms, out-pacing native species.
  3. Extreme climate events: The change in disturbance regime, e.g. heat waves, increase storms and floods, as a result of climate change favours the introduction and spread of INNS. Disturbance from storms can open up space, and INNS are likely to colonise more rapidly than native species. In addition, greater resilience of INNS to extreme weather might further facilitate their spread;
  4. Opening of new pathways: Climate change is also opening new pathways of introduction. For example, the melting of Arctic sea ice is leading to emerging Arctic shipping passages which greatly reduces the time taken for ships to travel from Asia to Europe. This could facilitate a greater east-west spread of INNS due to increased transport, and will increase the risk of INNS surviving the shorter journey.
  5. Unknown future invaders ‘sleeper species’: These are non-native species currently present but not invasive, as their growth and survival is limited by the current climatic conditions. However, they may become invasive with climate change. For example, the acorn barnacle Austrominius modestus is a cold-intolerant species first introduced to the UK in 1955, but did not became invasive until about 50 years later, following a series of mild winters. Similarly, in some cases native species can become a nuisance under climate change by expanding their range and altering the ecosystem dynamics at a new site. These are termed ‘neonatives’.
  6. Reduced resilience of native species: INNS can reduce the resilience of natural habitats to climate change by exacerbating any environmental stress. Conversely, climate change can reduce the resilience of habitats to biological invasions. There is also evidence that increasing numbers of INNS may even contribute to climate change in instances where they impact species acting as carbon stores (e.g. seagrass, or forests (Seidl et al., 2018))
  7. Challenges of management: The management of invasive species may become more challenging if their fecundity, resilience to management (e.g. regrowth potential) or resistance to treatment increases under climate change. For example, there is potential for an uncoupling of biological control mechanisms.

How can we manage INNS with climate change?

In response to the threat of INNS, many governments are developing biosecurity strategies aimed at preventing the introduction of new INNS. Biosecurity is the management of the risks posed by introduced species, using measures to prevent their introduction, stop their spread and limit the impact of established species.

However, to fully address the combined impacts of INNS and climate change, we will need to develop strategic and adaptive policies that address how climate change will impact invasive species and how their interaction will affect native species communities and habitats.

To achieve this, policy will need to be proactive to include the regulation of future potential invasive range shifts, streamline the regulatory process to include new species in these regulations when required and include invasive species issues in climate change policy and planning.

Risk management action also needs to be taken at the local level:

  • Biosecurity Planning: Preventing the spread of invasive species into more susceptible environments requires an awareness of the types of species that pose a threat to a particular ecosystem. As such, identifying and prioritising areas vulnerable to INNS establishment is key. This could include identifying areas within a jurisdiction, such as a port, which may be more susceptible to INNS entry.
  • Preventative management: Preventing establishment and early eradication are recognised as the most cost-effective way of managing INNS. Creating a watch list for potential range shifting invasive species and guidance of how to identify them for quick, active management should they become present within an area. A biosecurity management plan can help identify these watch list species and initial management actions should an INNS be identified;
  • Treatment and controls: Understand the potential controls which might be required should an INNS be identified, and incorporate resistant and diverse treatment methods to account for the fact that current methods may not be effective in the future, and be able to conduct rapid responses when range shifting species are detected; and
  • Education and outreach: Keep up-to-date on information and tools to incorporate climate change into invasive species management and share best practices with colleagues, stakeholders and researchers.

Risk-based monitoring in areas of potentially high exposure to the introduction of INNS may aid in the early detection, and higher likelihood of successful eradiation. Such actions would sensibly integrate into Biosecurity Plans which could help to focus the required control measures at individual sites and ensure that appropriate and efficient management actions are carried out.

Although there is not, at present, legislation enforcing the preparation of Biosecurity Plans, having a robust plan is compliant with other national and international legal commitments and is recommended best practice.

We routinely encourage developers to consider biosecurity planning as a mitigation measure for marine operations and developments. Our environmental specialists have developed with regulators a series of biosecurity plan templates from which developers and operators can draw.

Prepared by Vicky West, Marine Ecologist

Pictured: a tunicate colony of Didemnum vexillum; thought to be native to Japan, it has been reported as an invasive species in Europe, North America and New Zealand.

ABPmer advises Governments, advisory bodies and NGOs on marine environmental policy matters and has a long history supporting government and its agencies in developing the evidence base against which policy decisions are made.