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There are no barriers to prevent marine invasive species

Ash dieback, oak processionary moths, waterway minkes and parrakeets in Kew Gardens – there are plenty of species on and even above ground in the UK that didn’t originate in the country. The fifth Annual…

Tiny Japanese skeleton shrimp Caprella mutica, found in concentrations up to 300,000/m2. SAMS

Ash dieback, oak processionary moths, waterway minkes and parrakeets in Kew Gardens – there are plenty of species on and even above ground in the UK that didn’t originate in the country. The fifth Annual Report Card, drawn up by 150 experts at 55 institutions and released today by the Marine Climate Change Impacts Partnership, provides a hit list of non-native and invasive species that live in British waters.

The past few decades have seen an exponential increase in the spread of non-native species worldwide. In UK and Irish waters, alien species are on the increase, and many more are likely to come. Some will expand their range, some could have an impact on the environment or economy, and some are just plain revolting.

Non-native species are species that have been intentionally or unintentionally introduced to regions outside their usual, natural range. The increasing number of species appearing in ecosystems far from home is linked to the huge increase of human mobility, particularly the growth of fast international shipping that can carry species around the world quickly enough that they survive the experience, and thrive.

If a newly introduced species becomes established and begins to threaten biodiversity, cause economic damage, or both, they are called “invasive”. Biological invasions are one of the greatest threats to marine biodiversity and can be economically and ecologically devastating.

In from the east and west

There are now more than 90 non-native species known to live in British coastal waters and brackish waterways. Of these more than 60 are established, and several are considered to be high impact, either environmentally, economically or both, and some of them are still spreading. For example, the tiny zebra mussel enters and blocks industrial pipes that flow into the sea, on occasion shutting power stations down.

Alternatively, the carpet sea squirt Didemnum vexillum and leathery or Asian sea squirt Styela clava have become major problems to fishing and oyster beds – and look pretty horrible too.

Didemnum vexillum, also known as ‘Marine Vomit’. SAMS

Already in Britain, non-native species are estimated to cost the economy £1.7 billion a year, with the annual cost to industries such as shipping and aquaculture estimated at almost £40m. This is probably an underestimate, as little distinction is made between native and non-native species when crews remove hull fouling organisms from ships, or carry out pest control at fish and shellfish farms.

Brought back from the Korean War, Styela clava interferes with oyster beds and fouls ships' hulls. SAMS

Most alien species in the UK were initially seen in the English Channel and have since expanded northwards into the North Sea to the east of the country, and the Celtic Sea to the west.

Trade is mainly responsible, with creatures and plants transported in water and sediments sucked into ships’ ballast tanks, on fouled hulls, and in imported cargo. Port and marina developments, greater use of boats for leisure, and aquaculture all pose risks too.

As our knowledge and understanding of invasion biology improves, we have learnt the origin of many species now in British waters, using DNA marker techniques to provide more precise methods of tracking alien species. The two main origins for non-native species are the North Pacific and Northwest Atlantic. Species from similar regions are more likely to become established and widespread. There are, however, species like the zebra mussel Dreissena polymorpha from the region around the Caspian and Black Seas, and the tubeworm Ficopomatus enigmaticus from the Indo-Pacific, that can tolerate a wide range of conditions and are successfully established in British waters.

Where the invaders have landed, from the 2009 survey. SAMS

Warming seas invite visitors

Climate change and some extreme weather conditions have also enabled some non-native species to become reproductively successful in the North Atlantic, such as the Pacific oyster Crassostrea gigas. Climate change can influence every stage of the invasion process, but because of a lack of data it is often difficult to attribute, for example, shifts in distribution or increased reproductive success, directly to climate change. Others, including the bryozoan Bugula neritina, have taken advantage of warmer waters to become established beyond the warm waters around the outflows of power stations.

Regional climate models predict the current trend of warming will continue throughout this century, encouraging more and greater variety of non-native species into British waters. In order to avoid or lessen the impact of invasive species, it’s critical that we better understand how changes in seawater temperature, increased atmospheric CO2, increased rainfall, heat waves, storm frequency, and ocean acidification will influence how easy it is for invaders to establish themselves in British waters.

Despite a full list of non-native species living in British waters, there’s still a lack of long-term data and in-depth biological information, a worrying shortage of skilled taxonomists to help identify species, and gaps in our knowledge – gaps that researchers at groups such as SAMS, the Environmental Research Institute, NAFC Marine Centre and Marine Biological Association are striving to fill.