Marine non-native species

Invasive non-native plant and animal species are one of the greatest threats to biodiversity worldwide. They can have negative impacts on native species and can threaten whole ecosystems causing serious problems to both the environment and the economy. In Scotland, there is a growing problem with marine invasive non-native species

What species are here?

There are a number of non-native species already present in Scottish waters. Few of these are invasive, but there are a number that have become widespread and well established, including:

• Green sea fingers  (Codium fragile subsp. tomentosoides)
• Common cordgrass   (Spartina anglica)
• A red alga  (Heterosiphonia japonica)
• Wireweed (Sargassum muticum)
• Acorn barnacle  (Elminius modestus)
• Japanese skeleton shrimp   (Caprella mutica)
• Leathery sea squirt   (Styela clava)
• Carpet sea squirt  (Didemnum vexillum)

What other species are likely to arrive?

The following examples are species that are in, or are close to, the British Isles but have yet to reach Scotland:

• Chinese mitten crab   (Eriocheir sinensis)
• Slipper limpet  (Crepidula fornicata)

What problems do they cause?

The potential impact of invasive non-native species at sea can be significant, resulting in both biodiversity and economic implications. Away from their native habitats, invasive species are often able to grow very large and very quickly and can displace native species. They can become the most dominant species in the area and some can smother other creatures.

Invasive species can have impacts on our marine industries. For example, invasive seaweeds can grow on structures such as piers, slipways and fish-farm cages, and can become entangles in boat propellers. Other species can kill or compete with species used for aquaculture, and can spread disease.

How do they get here?

There are a variety of activities that can transport non-native species around the world and contribute to the spread of species between regions. These include: shipping (attached to boat hulls or in ballast water); the transport of fish and shellfish for the seafood industry; scientific research and public aquaria. The release of non-native species can be either accidental or intentional.

How do we deal with them?

Once established, it is extremely difficult to get rid of an invasive species in the marine environment. It is therefore more important to prevent the species arriving here in the first place. If a species does arrive in our waters, early detection is essential if any attempt at clearing is to be made. Once a species is abundant or widespread, eradication is likely to be impossible, except in local areas.