MCCIP ARC Science Review 2010-11 – Intertidal Habitats and Ecology

EXECUTIVE SUMMARY

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.

Mieszkowska, N., 2010. Intertidal Habitats and Ecology in MCCIP Annual Report Card 2010-11. MCCIP Science Review 19pp. www.mccip.org.uk/arc


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