About Marine Invasive Species

Defining Marine Invasive Species
Vectors of Introduction
Detection and Monitoring


Defining Marine Invasive Species
What are marine introduced (non-indigenous) species?

Introduced species are officially defined as ‘plants and animals that have been intentionally or accidentally inserted by human activity within or outside a national jurisdiction’. Since humans have broken down natural barriers with transport mechanisms such as international cargo ships, these species are being transported far beyond their natural range. In other words, an introduced species is a plant or animal that has been ‘introduced’ by humans into an area where it is not normally found. Species can be introduced both on land environments (terrestrial) and in the water (freshwater and marine).


What is the difference between introduced and invasive species?

When introduced species become established in their new environment they are invasive. If they are able to adapt to new environmental conditions and multiply, they can become a threat to native species and disrupt the ecosystem. Only a small amount of species actually establish themselves but those that do are unlikely to have the same natural controls in their new environment that keep their population in check in their native environment, such as predators, diseases or ecosystem interactions. This means they tend to increase in number rapidly and take over new environments. Marine invasive species are recognised as one of the largest threats to global biodiversity. The other threats are: over exploitation of resources, physical alteration of habitat, marine pollution and global climate change.


What kind of ecological impacts do marine invasive species have?

These species compete with native species and therefore threaten their diversity and abundance. They can change whole ecosystem processes by upsetting the natural balance. This lowers the ecosystem’s ability to cope with different pressures and impacts. All of this can result in lower biodiversity and an unhealthy ecosystem. It is also believed that invasive species have caused extinctions in land environments but there is not enough evidence yet to prove that marine invasive species have caused extinctions in the marine environment.


Are damaged habitats more vulnerable to invasive species?

Invasive species are more likely to settle in habitats that have been damaged. For example the 1998 bleaching event killed 80-90% of the coral reefs in the Seychelles, leaving them more vulnerable to invasions. It is therefore important to protect marine environments from other human impacts because a healthy ecosystem will be more resistant to introduced species becoming established.


What kind of economical impacts do marine invasive species have?

If marine invasive species damage the abundance of native species and the ecosystem, the aesthetic quality of the environment will be affected. This may impact the tourism industry, which accounts for a large proportion of income in the Seychelles. They can also affect native fisheries by reducing the number of fish being caught, resulting in less income for fishermen. Finally they are very expensive to get rid of once they are established. They cost some countries millions and sometimes billions of dollars in damages and eradication efforts.


What kind of social impacts do marine invasive species have?

In addition to possibly affecting people’s livelihoods and jobs, marine invasive species can cause serious health problems. For example the bacteria that cause cholera can be carried in ships ballast water, which killed more than 10,000 people in South America. Introduced species, such as the Zebra Mussel in the U.S., have clogged water pipes for nuclear power and sewage treatment plants, and public water supplies, causing not only huge expenses but possible breakdowns in the basic utilities humans depend upon.


How do marine invasive species affect Marine Protected Areas?

Marine Protected Areas (MPA’s) are areas set aside to preserve and protect their biodiversity and resources. MPA’s are often chosen because they include important marine resources and habitats that the surrounding environment or humans depend upon. They are often located near ports and are therefore in close proximity to introduction points for marine species. Due to their high environmental values and the management efforts required to set up and maintain MPA’s, the impacts posed by marine invasive species can be highly detrimental to them.


What’s the relationship between climate change and marine invasive species?

Studies have found that climate change processes and effects favour introduced species in the terrestrial environment. Climate change can disrupt ecosystem processes therefore encouraging introduced species to become established. Climate change also intensifies the effects caused by invasive species, including competition with native species for resources and the alteration of native ecosystems.


Vectors of Introduction
What are the primary two ways marine species are introduced globally?

Most species are introduced by ballast water transfer and hull-fouling.


What is ballast water?

Ballast water is the seawater that is used to stabilise and balance cargo ships. When the ship has no cargo, it must be filled with water to stabilise it. When it is full of cargo, the ballast tanks are empty. Therefore, the water is loaded at one port, taking lots of marine species with it, and unloaded at another port, carrying these species and dumping them in new marine environments. Some of these species are able to tolerate the new environment, establish themselves and so become invasive. It is estimated that 7,000 species are carried around the world in ballast water everyday and 10 billion tonnes of ballast water is transferred globally each year.


What is hull-fouling?

A hull is the underside of a vessel, which provides a surface that species are able to settle and attach onto. When the vessels move, these species are transported to other areas of the world. This applies to all vessels, including cargo ships, sailing ships and fishing vessels. In isolated island nations like Hawaii and perhaps the Seychelles, hull-fouling introduces as many organisms as ballast water, if not more.


What are the other ways marine species can be introduced?

• Aquaculture: some species are intentionally introduced in captivity for food purposes that then escape into the wild and become established. A good example of this in the Seychelles is Oreochromis Mossambicus, a Tilapia fish that was introduced in the 1950’s as a food fish and is now officially an introduced species in the Seychelles.

• Live Seafood Trade: non-native marine species that have been bought as seafood can be intentionally or accidentally dumped into local waters. These species or the parasites living on them may then become established and invasive.

• Use of plants for fish and bait nets: plants can be used as packing for fish bait and fishing nets. If these nets and bait are used in an area where the plants packed on them are not normally found, the plants may become introduced into the new area.

• Aquarium introductions: some species have been accidentally introduced when they have been brought into the country for aquarium use. A good example of this is Caulerpa taxifolia which is an alga that was introduced into the Mediterranean by mistake from an aquarium and now overgrows 13,000 hectares of seabed and competes with native plant species for food and light.

• Intentional introductions: some species may be introduced intentionally, for example to help increase fishing in local waters- these species can become established (invasive).


Detection and Monitoring
Where are introduced/invasive species likely to be found in the Seychelles?

In degraded coral reefs, ports and shipyards. Coral reefs are generally close to port environments, making them susceptible to introductions from commercial and recreational vessels.


Why must research surveys be undertaken to detect marine introduced species?

Baseline surveys must be undertaken to establish how many introduced species are present. Following the baseline survey, all detected species must be monitored over time to see if they are increasing in abundance and distribution, becoming established and/or causing damage. In addition surveys must be undertaken continuously to determine if new species are being introduced, which must then be monitored. Assessing the impacts of these species is difficult as it requires long-term monitoring. Also the potential effects of these species are not fully understood due to the difficulty in studying them and identifying their specific local impacts.


How do you find marine introduced species?

Using one of the following underwater scientific survey methods: traps, pile quadrat scrapings, plankton nets, diver transects, beach seine nets, anaesthetic (clove oil), gill nets and benthic grabs. Most of these methods can be used in a variety of underwater environments, including ports and coral reefs. However, coral reefs require additional survey techniques because they are complex environments with cryptic (hidden) habitats that are often larger scale and more complex than port environments.


Why is it important to monitor both ports and coral reefs for introduced species?

It is important to assess both ports and coral reef habitats because marine species are often introduced in ports with coral reefs in close proximity to them. Coral reefs are also sensitive ecosystems and so are vulnerable to introductions. Both habitats are economically important and already have other human impacts affecting them.


Why must marine invasive species be detected early?

Marine invasive species can spread rapidly and cause ecosystem level impacts therefore management of detected species and eradication is more successful if detected early. In addition once established, marine invasive species are very costly and difficult, sometimes impossible, to remove.


What can be done about marine invasive species?

  • Prevent the introduction of species, especially from ballast water and hull-fouling.
  • Minimise the transport and exchange of species and find possible treatment technologies for both ballast water and vessel hulls.
  • Undertake research surveys to detect introduced species early.
  • Monitor introduced species and determine what impact they have on the local environment.
  • Increase knowledge and awareness about introduced species.
  • Control them once they are established. However this is very expensive and only works if done early enough, therefore prevention is a better solution.
  • International collaboration for this global problem is also essential.


What measures are in place to address the problem of marine invasive species?

Different countries have different regulations for ballast water and hull-fouling and research is being undertaken to find the best solutions. In general little management is presently done about the problem of marine invasive species due to a lack of awareness, financial resources and technical capacity.

International regulations to reduce ballast water are voluntary and so only decrease the risk but do not solve the problem completely. To reduce the damage caused by these species governments, private industries and individuals need to address this problem with more urgency to prevent introductions rather then simply deal with the consequences.


Can I help as an individual in the Seychelles?

Yes, you can:

  • Raise awareness about the problem.
  • Encourage the monitoring of your local harbours and coral reefs.
  • Support measures to prevent the transport and exchange of ballast water between harbours.
  • Contact the SCMRT-MPA in the Seychelles for more information or if you see something suspicious in Seychelles waters.

  • Zebra Mussels

    Zebra Mussels

    Photo: IUCN

  • Boat carrying invasive species

    Boat carrying invasive species

    Photo: IUCN

  • Ameer Abdula sieving

    Ameer Abdula sieving

    Photo: Ameer Abdula

  • Team sorting in lab

    Team sorting in lab

    Photo: IUCN