Aliens – they’re over here, and they’re here to stay! Some take up prime residential space; others quite literally live on top of each other, and other organisms. Some of them cause real environmental and economic damage. While most, if not all, are impossible to eradicate, there may be ways to minimise how much harm they cause, if we can just work out how. MCS is working with MarLIN (the Marine life Information Network at the Marine Biological Association), to find out more about them.
Download a copy of the Marine Non-native Species ID Guide
How did they get here?
The most common transport method is shipping, as hitch-hikers in ballast waters, or attached to boat hulls. Some got here as invited guests, usually for commercial projects such as oyster farming, which themselves may have a travelling companion species or two associated with them. It is possible that others could arrive here on drifting material, including plastic debris, or be released from aquaria.
Why do they stay?
Some really take a liking to conditions in our shallow seas. A number of species come from equivalent latitudes in the North Pacific, but others hail from temperate southern seas as far away as Australia and Japan. If a species arrives and can reproduce, it has a chance of long-term establishment – and if it has left its main predators or grazers behind, its growth and spread can go ahead with only physical limitations.
What harm do they do?
Conservation biologists generally view alien introductions as something that should be avoided. A recent scientific report for the United Nations ranks alien introductions as the second biggest threat to native biodiversity, behind only habitat loss.
A few have a big impact on shellfish fisheries, while others may make home on boat hulls, within pipes, and even foul moving parts such as propellers. One, the Chinese mitten crab, even excavates under stones, disturbing riverbank substrates in a way that could justly be described as vandalism!
Most of the 65 or so aliens we know about live on the seabed, and some may simply take over the living space that other life would have colonised – Sargassum may do this and shade much of the space around it.
Please report your sightings via any one of the following resources: