Non-native species (NNS) are plants, animals and other organisms that have been found living outside of their natural geographic range. Some of these NNS are termed invasive because they are capable of having a serious negative impact on the environment, economy and even human health. The Convention on Biological Diversity cites non-native species as being the second greatest threat to the global environment after habitat loss.

A 2017 study found 39 marine NNS in Jersey, all of which had probably arrived in the Island from established populations in the UK or France. All of these were assessed for their potential impact on local habitats, species, human health and the economy and given a threat score. From this study, 14 NNS were considered to be having a moderate to significant negative impact on the local marine environment and were therefore considered to be invasive. These include seaweeds, molluscs, sea squirts and crustaceans.

At least two field studies are made for NNS annually and the assessment process is repeated.