New species of fauna, flora or unicellular organisms that are not indigenous and become established in the waters around the UK are termed marine non-natives. Some of these species can be considered to be invasive if they spread rapidly and cause economic or environmental harm, or harm to human health. Most introductions have arrived via human intervention, intentional or otherwise (e.g. aquaculture, ballast water).
More recently due to climate change some species have expanded their ranges to become established in new regions and some already introduced species have been able to take advantage of warmer conditions to become more abundant.
There is little evidence to suggest that marine non-natives in the UK have caused extinctions of native organisms. Localised impacts have included sporadic poisoning or smothering of farmed organisms in aquaculture, clogging of nets, or fouling of structures - all events of considerable concern for the aquaculture industry.
The invasive Chinese mitten crab introduced by man from Asia (found in 1935 in the Thames) lives in both estuaries and rivers in the UK and is becoming a major pest and predator on native species including young fish.
Colonisation by Chinese mitten crabs has greatly increased in the UK in recent years due to warmer temperatures.
In the case of the Chinese mitten crab, climate change did not lead to its introduction but has been implicated in its more recent rapid spread.
Key link to 'Coastal economies and people' as sea defences can act as stepping stones for non-natives moving in response to climate change.
The Pacific diatom Neodenticula seminae arrived in the North Atlantic in 1999, after becoming locally extinct 800,000 years ago.
This could be the first evidence of a trans-Arctic migration in modern times.
It is a possible harbinger of a potential inundation of new organ isms to the North Atlantic as sea ice cover decreases.
Introduction of Pacific species to the N. Atlantic could also have an impact in the longer term through competition and hybridisation of the fauna and flora native to the UK.
Key link to 'Arctic sea ice' as reduced sea ice cover enables Pacific species to move into the North Atlantic.
Expansion of warm habitat
The 10°C isotherm in the North Sea has moved northwards at an approximate rate of 22 km per year since the 1960s.
The environment is now more suitable for warm-temperate species, which have been increasing in abundance.
It is possible that in the near future, traditional fish stocks in the North Sea (e.g. cod) will be replaced by smaller pelagic fish stocks (e.g. s ardines and anchovies).
Key link to 'A view from above' through northward movement of fish stocks.
Regional case studies for Ireland, Scotland, Wales and England are detailed in the full review document.
Consequences and likely future changes
It is possible that in the near future traditional fish stocks in the North Sea (e.g. cod) will be replaced by smaller pelagic fish stocks (e.g. sardines and anchovies).
In the case of the Chinese mitten crab, climate change did not lead to the introduction but has been implicated in its more recent rapid spread.
Introduction of Pacific species to the N. Atlantic could also have an impact in the longer term through competition and hybridisation of the fauna and flora native to the British Isles.
Non-natives can have an economic impact on fisheries and aquaculture (e.g. the recent jellyfish bloom off Ireland, and new Harmful Algal Blooms, see the full online review for more details).
PHOTOS: Rohan Holt/CCW, P. De Oliveira/Photolibrary.