Rocky Shore - Threats

There are a number of pressures on rocky shores and and the species which inhabit them in Scotland and along the East Coast, including invasive non-native species, climate change, coastal 'squeeze', pollution, and disturbance (Austen et al, 2011; Lake et al, 2015; Scottish Seabird Centre, n.d.).
 

Key Threat: Climate Change
Climate change is causing changes in rainfall, temperature, weather patterns and sea level and this in turn is impacting rocky shore habitats and species. Coastal rocky intertidal species distribution is being altered in response to temperature rises particularly with warm water 'southern distributed' invertebrates and macroalgae extendeding their range northwards in Britain and along Scottish coastlines (Mieszkowska et al, 2006; Austen et al, 2011). In comparison, northern cold water species are experiencing reducations in range and abundance especially at southern limits of their distribution (Austen et al, 2011). For example, Poli's stellate barnacle (Chthamalus stellatus) has increased its distribition and range in Scotland and along the East Coast by small amounts between 2002-10 and 2014-15 (fig. 1) (Scottish Government, 2020).

Rising sea levels due to climate change may result in 'coastal squeeze'. As rocky shores are a static habitat, rising sea levels are changing the zonation of rocky shores with suitable conditions for upper shore specialist species disappearing as sea level rises. Eventually rocky shore habitats may be swallowed by the sea altogether.

Key Threat: Pollution
Pollution, particularly from human sources such as agricultural and urban run-off and sewage effluent can have a big impact on rocky shore species as it can introduce harmful chemicals and excess nutrients to a site (Lake et al, 2015; Scottish Seabird Centre, n.d. ). Sewage discharges can lead to a rise in seawater temperatures and a decrease in pH levels, salinity, and dissolved oxygen in the water. All of this has an impact on rocky shore invertebrate and macroalgae diversity and abundance, and can change the structure of the rocky shore ecosystem. For example, species which benefit from the additional nutrients from sewage such as small periwinkle (Melarhaphe neritoides) will increase in numbers, increasing competition for food and space on rocky coastlines (Cabral-Oliveira et al, 2014).

Key Threat: Invasive Non-Native Species (INNS)
INNS are an increasing threat to Scottish coastlines and rocky shore habitats. The impacts of INNS on native species are poorly understood, but INNS are likely to increase competition for resources such as food and habitat - potentially impacting on native species distribution and abundance (Austen et al, 2011). A number of key marine INNS recorded in Scotland have not been recorded on the East Coast, however the orange-tipped sea squirt (Corella eumyota) has been recorded near Stonehaven in 2019 (fig 2).