• The UK's territorial deep sea covers a huge geographical area and supports a wide range of environments and biological communities. The deep sea is remote, difficult and expensive to study and as a result our understanding of its ecology is still limited.
• Deep-sea ecosystems carry out a range of ecosystem processes which are essential to global biogeochemical cycling (e.g. carbon cycling).
• There are no long-term datasets showing the extent of natural biological variability over time in UK deep waters. This makes it difficult to predict future climate-driven changes.
• Deep-sea ecosystems are intricately linked to processes at the sea surface, as almost all deep-sea animals are dependent on plankton sinking from surface waters for food. Climate-driven changes in surface processes will therefore have a direct impact on deep-sea ecosystems.
• Studies on the Porcupine Abyssal Plain show that deep-sea communities are far more dynamic than once believed. Population explosions of some invertebrate species are thought to have been triggered by increases in the quantity of food reaching the sea-bed in particular years, which has been linked to climate variability.
• Plankton communities in the north-east Atlantic may already be demonstrating climate-driven changes. While corresponding changes in productivity will affect the supply of food material to the deep sea, it is difficult to predict the consequences for deep-sea ecosystems.
• While ocean acidification poses a major long-term threat to deep-sea corals and other calcifying organisms, at present we have very few data on which to base detailed predictions of future impacts.

What is already happening: Low

We have clear evidence that major benthic community changes have occurred on the Porcupine Abyssal Plain and there is compelling evidence that these changes are related to changes in export flux of organic matter from the surface waters related to climate variations (i.e. the North Atlantic Oscillation). Export flux, seasonality and rate of organic matter recycling in the euphotic zone, are likely to be significantly affected by climate-driven changes in the surface ocean in UK waters. However, the "Amount of evidence" is rated as Low to reflect the fact that the available north-east Atlantic data are confined to the PAP and we have no comparable information from any other localities in the UK's territorial deep sea.

What could happen: Low

The lack of any long-term data sets giving information on background temporal variability of deep-sea biological communities in Regions 4, 7 and 8 justifies a Low rating for "Amount of evidence". "Level of agreement" is rated as Medium to reflect the general consensus that climate-driven changes in surface ocean primary productivity and export flux are likely to occur and will have consequences for deep-sea ecosystems, although detailed predictions of the pattern of change are not possible.

The top priority knowledge gaps that need to be addressed in the short term to provide better advice to be given to policy makers are:

1. Lack of baseline data on natural temporal variability of deep-sea biological communities in Region 8. There is an urgent need for more time-series data to detect and monitor ecosystem change. The archived data and unprocessed samples from the SAMS Rockall Trough stations, surveyed at intervals from 1973 to 1995, should be analysed with a view to re-starting this time-series. Long-term monitoring should also be established in the domain of Arctic water outflow in the Faroe-Shetland Channel/Wyville Thomson Ridge Region.
2. Limited understanding of the ecosystem effects of benthic community changes in the deep sea. This should be addressed by maintaining the PAP-SO time-series sampling of phytodetrital flux and benthic population abundance/biomass, supplemented by measurements, in situ experiments and ecological modelling (as appropriate) of important ecological processes such as organic carbon turnover and burial, bioturbation, food web dynamics and reproductive output of benthic organisms.
3. Limited information on the distribution and structure of benthic biological communities in Region 8. While the baseline surveys carried out under the Strategic Environmental Assessment (SEA) programme in the Faroe-Shetland Channel (SEA4) and Rockall Trough (SEA7) there is still a lack of data on the range and distribution of deep-sea faunal communities within UK waters.

Attaching a monetary value to the deep-sea is problematic for several reasons: the limited knowledge of deep-sea ecosystems and the goods and services they provide, the complexity of the ecological processes as well as the broad time- and space-scales over which they operate, the nature of deep-sea ecosystems, especially those with significant option-use values for which it is difficult to derive a monetary value, and the fact that people have practically no first-hand experience of deep-sea ecosystems, so valuation methods based on preferences are likely to be biased or irrelevant (van den Hove, 2007).

While there are unlikely to be any direct socio-economic impacts arising from the ecosystem changes discussed here, the deep sea provides a number of important ecosystem functions which may alter in response to climate change. In particular, the deep sea plays an important role in the global carbon cycle, and mediates the removal of carbon from the global carbon cycle into the geological record. The deep-sea also provides a range of ecosystem goods and services (i.e. human benefits directly or indirectly derived from ecosystem functions). Maintenance of biodiversity is thought to be essential to ecosystem stability, so that loss of species may detrimentally influence ecosystem function, and therefore the provision of goods and services (van den Hove, 2007).

Certain components of the Total Economic Value of the deep seas such as oil and gas extracted or fish harvested are relatively straightforward to value through market prices. However, the majority of deep-water biotic resources have slow growth rates such that their exploitation is much like that of abiotic resources; that is, they should be considered as non-renewable. Climate-driven changes in the deep sea of Region 8 are likely to affect commercially-exploited demersal fish species such as orange roughy (Hoplostethus atlanticus), roundnose grenadier (Coryphaenoides rupestris) and deep-water sharks. This is the only living resource currently exploited in the UK's deep sea. Stocks of these fish species have been massively depleted by unsustainable levels of trawling (Gordon, 2003; Bailey et al., 2009). Current fishing pressure is much reduced, with populations possibly stabilizing at much reduced levels (Neat & Burns, 2010).

Hughes, D.J., & J.A. Hughes (2010) Deep-sea habitats and ecology in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 11pp. www.mccip.org.uk/arc