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Marine Invasive Non-Native Species (INNS)

The introduction of INNS is widely considered to be a major threat to marine biodiversity. Invasive species have the potential to cause a range of detrimental biological effects such as altering community structure, modifying habitats and outcompeting/displacing native species1. They may even decrease economic production through interference with fisheries, aquaculture or marine infrastructure2.

As a small island, the Isle of Man is potentially at greater risk of the negative impacts of marine invasive species. This is due to the ecological ‘naivety’ of native species and because there are fewer native species capable of outcompeting or predating on invasive species. Species of particular concern include the killer shrimp (Dikerogammarus villosus)(which can inhabit brackish waters up to 20%, ie. river-influenced harbours) and the carpet sea-squirt (Didemnum vexillum) which have become established in the UK and incur significant management costs. In response to the threat of marine INNS a Marine Biosecurity Plan has been developed. Prevention, surveillance and control are key features of the plan that aims to reduce the impact of marine invasive species in Manx waters. Work is also underway to develop a Marine Biosecurity Implementation Plan, along with Species-Specific Action Plans, which outline the processes and procedures that will occur upon detection of a significant threat.  

The Manx Wildlife Trust (MWT) also participates in this area through the collection of marine invasive species sighting information in order to map their distribution and spread. The downloadable MWT Marine Invasive Species ID Guide describes 20 invasive species and where to report sighting information, should any of them be observed around the Island.

For further information please visit;

Citizen science - Invasive non-native species

Report non-native species on the NBN website

Contact Details (Marine INNS)

DEFA (Fisheries and Marine Environment)

Telephone: +44 1624 685884

Manx Wildlife Trust (Marine and Freshwater Officer)

Telephone: +44 1624 844432 


(1)   Molnar, J.L., Gamboa, R.L., Revenga, C., Spalding, M.D. (2008). Assessing the global threat of invasive species to marine biodiversity. Frontiers in Ecology and Environment, 6, pp. 485-492.

(2)    Bax, N., Williamson, A., Aguero, M., Gonzalez, E., Geeves, W. (2003). Marine invasive alien species: A threat to global biodiversity. Marine Policy, 27, pp. 313-323.

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