Life on the edge – seashore and coastal habitats
The Community of Arran Seabed Trust (COAST) is running a year-long media campaign to raise awareness of the many exciting habitats and species to be found in Arran’s seas, many protected by the South Arran Marine Protected Area. Each month, they will focus on a particular habitat or collective group of inter-linked species. Their August article features seashore and coastal habitats. There is more information on COAST’s social media or visit www.arrancoast.com.
The hot sunny weather over recent weeks means many of us have been spending time on the beach and enjoying a cooling dip in the sea.
While relaxing and enjoying time there, it may not be immediately obvious that the coastal fringe is one of the more extreme environments for Arran’s marine life to live in.
The seashore is a particularly challenging habitat for animals and plants to live in as they have to survive being repeatedly submerged and exposed to the air as the tide ebbs and flows. During the summer, this can mean extreme changes in temperature and other conditions. In winter, the forces involved as waves crash onto the shore during storms requires other adaptations.
Opportunities
The tidally swept seashore is often referred to as the ‘intertidal’ – the area between high and low tides – and it presents unique opportunities to explore the local marine life without having to go underwater. The creatures and plants that can be seen at low tide are fascinating and there is also the possibility when looking seaward of seeing larger marine animals such as those described in last month’s Banner article.
Marine species vary from the high to the low water mark, reflecting the tolerance of different animals and plants to the varying conditions. This creates a pattern of biological zones across the shore and is most obvious on rocky shores where bands of different seaweed species and barnacles can be visible. Whilst it is less obvious on sandy shores, as the marine life is buried in the sand, similar zones exist.
Species best adapted to survive long periods exposed to the air or, conversely, terrestrial species that can survive the influence of salt water for short periods, are found at the top of the shore.
Most obvious are lichens, with patches of green, grey and yellow lichens able to occupy the most landward areas of rocky shore where other species can’t survive.
There are some particularly spectacular upper shore lichens along parts of Arran’s west coast. Below the lichen zone is a brown seaweed called channelled wrack which, as its name suggests, has a channel along the length of the fronds. This species spends up to 90 per cent of its life out of seawater and has adapted to its place on the shore to such an extent that it dies if kept permanently submerged.
Zones
Moving seaward from the channelled wrack, the subsequent zones are identified primarily by the presence of other brown seaweeds in turn: spiral wrack, bladder wrack, egg wrack, serrated wrack and finally kelp which, while not really a seashore species, can be seen emerging from the water on very low tides.
The collapsed clumps of seaweed that are seen when the tide goes out help to retain moisture within the plants, meaning that species including flat top shells and even some small fish, such as shannies and butterfish, can survive under the damp seaweed until the tide comes back in. The seaweed species present on our shores and their growth say a lot about the nature of a shore. In more exposed locations, some of the large brown seaweeds modify their shape – bladder wrack, for example, loses its characteristic gas bladders, so there is less drag on the plants in rough seas. In more sheltered conditions, egg wrack is likely to be more abundant. In very sheltered situations, such as those found in the inner parts of Lochranza, there is a specialised free-living form of egg wrack, crofter’s wig, which is able to survive even though is not attached to anything.
As with seaweeds, seashore zones favour different animal species which have adapted to live in this turbulent environment. Molluscs such as winkles and dog whelks – sea snails – have a hard ‘plate’ which they close and use to seal their shell to prevent them from dehydrating. The beadlet anemone protects itself when the tide is out by pulling in its tentacles and forming a rounded, jelly-like red or green blob on the rock.
The topography of the shore is also important. Overhangs and crevices provide cool, damp shelter for species such as dog whelks, anemones and sponges when the tide is out and spaces under boulders provide hiding places for starfish, crabs and fish. Rockpools often provide a foothold for animals and plants that would otherwise not survive on the shore. They can be particularly rich in marine life and provide a glimpse into the submerged world beyond the low water mark.
On Arran, the Lamlash Bay No Take Zone and South Arran Marine Protected Area are helping protect parts of our seashore habitats. Given the natural stresses that it has to endure, we might think of seashore marine life as being fairly robust, but it can be as easily affected by human activities as those underwater. Extreme weather and warming seas pose serious challenges for species exposed to both water and air. As sea levels rise, where man-made and natural obstructions such as roads, buildings and cliffs prevent seashore habitats extending landwards, we are likely to lose substantial areas of intertidal habitat. Pollution from land and sea and dumping of waste can also be a problem, as can activities such as extraction of beach sand and gravel from the shore.
While we generally explore the seashore when the tide is out, exploring it by snorkelling when the tide comes in provides a completely different perspective. Flattened clumps of seaweeds are transformed into magical floating meadows and small fish, crabs, starfish and other marine life busily go about their business in the window of opportunity provided by the rising tide. Even barnacles come alive when submerged, their feather-like feeding legs combing the water for microscopic organisms.
There are plenty opportunities to enjoy the marine life on Arran’s shores but take care not handle or disturb the species. Some animals like limpets and shannies have ‘homes’ to which they return to as the tide goes out.
Join COAST on one of our shore scrambles to learn from a marine biologist or take a dip in the sea on Arran’s self-led Snorkel Trail to see the magical shore life beneath the waves.