Multiple climate-related drivers including temperature, sea-level rise, storminess and wave height are being documented to cause alterations in regional biodiversity, with increases in southern regional seas as warm water species extend their distributions faster than cold water species are retreating. As species are lost from areas, biodiversity is likely to decline, especially in habitats such as saltmarshes and seagrass beds where restricted connectivity between systems may limit propagule dispersal and inhibit the sustainability and recovery of impacted habitats. Although rocky intertidal habitats have a greater degree of connectivity, they are also at risk of regional biodiversity change as populations become established or disappear.

Changes in geographic distributions of intertidal species are continuing, with northern range limits of southern species in rocky intertidal habitats continuing to extend during the last 2 years. For example, the range limits of some southern species have moved up to 12km further north (e.g. Osilinus species) between surveys undertaken in July 2007 and July 2009. Population abundances of the topshell Gibbula umbilicalis have increased throughout the UK and in warmer southern areas they have switched to having two periods of gonad maturation per year (uni- to bivoltine). This was observed for the first time in 2008/2009. Such a strategy is more characteristic of populations inhabiting warm waters and lower latitudes. If the current responsive trend continues, shifts in dominant species of different taxa are likely to occur within the next decade. Established populations of cold water fauna are showing declines in abundance in the western Channel, but are still undergoing annual recruitment. The available evidence suggests that climate is acting on the adult reproductive stages and the post-recruitment stages of juveniles. Such information is not available at present for many soft sediment intertidal species.

Saltmarsh habitat is declining in the UK due to coastal squeeze, resulting from erosion at the seaward end of saltmarsh beds by increased storminess and relative wave height, and prevention of landward retreat by coastal defences built to combat increased flooding from storm surges. This is being offset in some areas by managed realignment and habitat recreation. Mudflats are at risk of rising sea levels and erosion, but more information is required to quantify the impacts on benthic composition and biomass. The dynamics of seagrass beds are different depending on their regional location, with increases and decreases in spatial extent occurring since 2007. Insufficient evidence is currently available to make a direct link between climate change and alterations in spatial coverage of Zostera habitats. There is little direct evidence for current impacts of climate change on soft sediment communities, but model predictions indicate a future loss of biomass and biodiversity.

Alien species already present on natural intertidal habitats are increasing in abundance. The few impacts on native species studied to date are predominantly negative but caution is urged in assuming that all introductions have adverse impacts for native communities, as some species can actually increase biodiversity.

Rocky intertidal systems are unlikely to be negatively impacted to a large degree by sea-level rise as most UK rocky habitats have sufficient habitat above existing high water springs levels to accommodate vertical shifts in biota in response to rising sea levels. Community compositions are changing due to loss or gain of species and changes in relative dominance, which have the potential to alter structure and functioning of rocky ecosystems. Artificial 'stepping stones' created by increasing numbers of coastal defences along areas of soft sediment coastline have led to species artificially extending their range and subsequent colonisation of natural shores beyond these regions, and more species are expected to use this route across areas of unsuitable habitat in the future.

What is already happening: Medium

What could happen: Medium

Overall

For this topic as a whole, we have a medium level of confidence both for 'what is happening now' and 'what could happen in the future'. Whilst we are collating more information for all of the habitats, we don't have sufficient biological (physiological / genetic) information yet to understand cause-and-effect, or the biological mechanisms by which most species are responding. There is a high level of confidence in conceptual and qualitative assessments, but quantitative information is still lacking for many intertidal habitats and this limits the predictive capacity for these systems.

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 broad-scale, integrated monitoring designed to detect the impacts of climate change- temperature, storminess, sea-level rise on soft and rocky systems.
2. Information on the impacts of drivers, especially temperature, sea-level rise, storminess and precipitation, on the productivity and carrying capacity of systems.
3. Insufficient knowledge of biological mechanisms by which species are responding to climate change from the cellular to ecosystem levels.

Costing the economic and social value of goods and services provided by intertidal coastal habitats and the communities they support is still in its infancy for the UK and wider European Union. The ecosystem goods and services provided by intertidal and other coastal habitats are currently being evaluated as part of work being undertaken for the upcoming National Ecosystem Assessment. An initial draft of this report will be produced early in 2010 and will allow us to identify more precisely the cultural, economic and other types of benefit provided by these ecosystems. Seagrass beds and macroalgae were given an estimated global economic value of $US 19,000 per hectare per year a decade ago (Costanza et al., 1997) making them some of the most valuable plant resources on the planet. This estimate is likely to be revised in the current assessment being undertaken by the Deutsches Bank.

European directives such as the EC Habitats Directive and Water Framework Directive require habitats and areas to be monitored against benchmark reference conditions. These policy drivers do not take into account the fact that climate change can alter ecosystems irrespective of other anthropogenic impacts, and a site may not reach target conditions even if the state of the site or habitat has remained the same or improved with respect to direct human pressures. For example, sea-level rise will negatively impact upon intertidal habitats with a shallow vertical gradient and therefore present serious problems in meeting the requirements of the Habitats Directive for specific sites. This is something that must be borne in mind when setting the criteria for Good Environmental Status for the Marine Strategy Framework Directive, which is currently in the planning stages. In addition, the loss of saltmarsh habitat creates an obligation under the EU Habitats Directive to create a similar area of replacement saltmarsh. This has economic implications for member states in addition to statutory obligations arising from these directives. An overarching requirement is harmonisation of the Water Framework Directive, Marine Strategy Framework Directive and the Habitats Directive and the understanding that climate change will necessitate the development of moving baselines in order to achieve Good Environmental Status against the pervasive background of climate change.

Mieszkowska, N. (2010) Intertidal Habitats and Ecology in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 20pp. www.mccip.org.uk/arc

Long-term time-series for rocky intertidal invertebrates allow changes in the location of geographic ranges to be tracked on an annual basis around the UK and Ireland. The northern limit of the warm water topshell Osilinus lineatus was cut back from north to south Wales and south England after the extremely cold winter of 1962/3. It showed little sign of recovery in the cooler decades but began re-expanding its range in the 1990s. The northern range edge has been continually extending during the 2000s, with a 12km shift from Anglesey to the north Wales mainland since it was last reported in the 2007-2008 MCCIP annual report card. The north-eastern range limit has also extended from Osmington Mills in Dorset to Kimmeridge, 19km east along the English Channel since 2002. Two individuals were first recorded at Kimmeridge in 2007 and in 2010 there is now a small, multi-age population. Abundances within populations around the UK have exponentially increased during the 2000s.