• There is evidence that climatic processes influence species abundance and community composition in soft-sediment habitats in the North Sea. There is no obvious signal of warming effects in sediments in southern and south-western areas where changes would be most expected. However, changes in crustacean abundance in some locations and the occurrence of previously undocumented species in others (e.g. brittle star Amphiura incana and shrimp Athanas nitescens) suggest some degree of climate-influence.
• Hard-substrate habitats in southern and south-westerly waters appear to be affected, with disease outbreaks in seafans, changes in algae distribution and abundance and the appearance and increased occurrence of a previously unrecorded warm-water barnacle all linked to increased seawater temperatures.
• Climate change is likely to impact the benthos in future. The changes documented in soft-sediment communities are expected to continue, and probably escalate, in response to the cumulative effects of seawater warming and ocean acidification. Species forming cold-water coral reefs and maerl beds may experience shifts in distribution as a result of intolerance to altered seawater temperature and chemistry, with knock-on effects on community composition and function.
• Future impacts on these habitats are likely to have socio-economic ramifications, as cold-water coral reefs and maerl beds are protected under European legislation and soft-sediment communities are an important food resource for commercial fish.
• There are knowledge-gaps in a number of areas. We are currently unable to fully assess the scale of benthic species and community responses in relation to climate change, understand links between impacts in benthic and pelagic systems or model future species distributions. An appropriate benthic monitoring and assessment programme, coupled with continued involvement in international initiatives, is essential for characterising climate impacts in UK benthos.

What is already happening: Low

Site-specific research provides strong evidence on the potential effects of climate change on benthic habitats and species in the Northern and Southern North Sea. Whilst this information is appropriate on a localised scale and for individual ecosystem components (e.g. plankton, fish, etc.), there is a need to understand how these components are linked and responding over larger spatial scales. There are indisputable gaps in coverage of some Charting Progress regions, where we have limited information on benthic status and potential responses to climate change. Additionally, in the areas where we currently have a comprehensive understanding of benthic species and communities, there is still a need to explore interactive effects of multiple human pressures (e.g. fishing, aggregate extraction, dredging and construction) as this information is essential for assessing the impacts of climate change in UK waters. Based on the reviewed information on current benthic state and gaps in knowledge, our confidence level is low.

What could happen: Low

We have indirect evidence of warming effects on maerl and Lophelia habitats, based on laboratory observations of temperature sensitivity in the individual species. However, there has been little direct observation of climate-related change in situ and we require more detailed understanding of how changes in the reefs and maerl matrices will affect the communities they support. The science relating to acidification effects on particular benthic species is sound, but further evidence is required on a wider range of species and whole-community and functional effects. We currently lack the capability to make quantitative predictions about the nature and extent of any future temperature-driven shifts in benthic species distributions. Hiscock et al., (2004) have developed a conceptual framework for identifying species potentially affected by future temperature increases and quantitative models for predicting future distributions have been developed for marine fish. However, we are, as yet, unaware of such models being developed for predicting future species distributions or community-level effects in marine benthos. The lack of such predictive capability for both warming- and acidification-effects makes it difficult to translate evidence on links between climate and benthos into forecasts for future conditions. Additionally, we have little understanding about the interactive effects of ocean warming, stratification and acidification. Based on this information, we place a low level of confidence in our predictions of what could happen in future.

Compilation of this review has identified some clear gaps in our knowledge of climate change impacts on shallow and shelf subtidal habitats and ecology. Generating insight into these areas will allow scientists to provide better advice to policy makers and support the implementation of climate-related policy.

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

1. There is a paucity of large scale benthic distribution data for UK waters, which hinders our ability to detect changes in species distribution over large areas of the seabed. Such information, when combined with experimental studies of the effects of climate warming and ocean acidification, will allow us to confidently describe patterns of benthic response to climate change.
2. The benthic and pelagic components of the marine ecosystem are inextricably linked, but we currently lack understanding of interactions between the components and their common responses to climate change. In order to understand the ecosystem-level consequences of climate change, we need fundamental research on the nature and extent of synchronicity between the benthos and pelagos, including higher trophic levels such fish, seabirds and marine mammals (e.g. food web assessments).
3. There is a real gap in our ability to make predictions about the responses of subtidal species and communities to future climate change. We have the capability to generate such information through statistical modelling techniques yet, with the exception of fish species, these methods remain largely undeveloped in shelf sea systems. We need to develop the capacity to model species' distributional responses to changing environmental conditions and a knowledge-base that will allow us to understand the underlying mechanisms and ecosystem-level implications of such changes.

Little information is available on the current or future socio-economic effects of climate change on shallow and shelf subtidal habitats and ecology. However, some general areas of concern can be identified based on the evidence presented in the review.

Marine protected areas

Although there is currently little evidence of warming-related subtidal species distribution shifts, any such shifts occurring in future will have socio-economic ramifications if they result in the movement of species of conservation concern outwith the boundaries of areas designed for their protection.

For example, maerl and Lophelia pertusa have restricted distributions in the UK and are protected under Annex I of the EU Habitats Directive - maerl habitats are qualifying features of the Sound of Arisaig, Loch nam Madadh, Strangford Lough and Fal and Helford marine Special Areas of Conservation (SAC), while Lophelia pertusa reefs are a primary features or features of the candidate Darwin Mounds SAC and North-West Rockall Bank and Hatton Bank draft offshore SAC (www.jncc.gov.uk). Others, such as the horse mussel Modiolus modiolus, the honeycomb worm Sabellaria alveolata and the pink seafan Eunicella verrucosa, also have restricted UK distributions and conservation importance at national or international levels.

Temperature-driven range contractions in these species may necessitate boundary-alterations, which are likely to be socially, politically and financially demanding. Range-expansions are likely to be less problematic, unless they introduce new species of conservation concern into UK waters. Even if temperature-driven changes do not result in such extreme scenarios, alterations in the abundance or spatial distribution of conservation species may affect the type and extent of future commercial and recreational activity permitted within protected areas.

Indirect effects on fish and fisheries

Many fish species feed on benthic organisms and climate-driven impacts on benthic communities have the potential to influence population dynamics of fish predators. If changing distributions or abundance of prey species have significant effects on numbers of commercially-important predators, this is likely to have economic repercussions for the fishing industry. However, there is little information available on the socio-economic value of benthic prey. Moreover, it is not currently clear whether fish predators and their benthic prey will respond in concert to changing seawater temperatures or ocean acidification, or how impacts on one trophic level will filter through others.

Birchenough, S., and J. Bremner (2010) Shallow and shelf subtidal habitats and ecology in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 16pp. www.mccip.org.uk/arc