How small creatures help shape our coast.09.03.2022
Our coastal cliffs form a line of defence against a constant marine onslaught. From Black Head to Doolin the Burren limestone meets the sea and from Doolin and the Cliffs of Moher to Loop Head our sandstones and shales from a formidable barrier. They are greeted with a barrage of Atlantic storms. The strength of these storms is such that the impact of the waves can be detected by the seismometer at the Cliffs of Moher Visitor Centre that is designed to detect Earthquakes on the other side of the world. These storm events cause coastal erosion during which boulders the size of cars are routinely thrown around.
For much of the year however, the coast is a pleasant place to live for humans and sea creatures alike. Along our coast a community of creatures live on the rocks that are submerged and exposed twice a day by tides. This is the place where we find the rock pools that give us a glimpse into life beneath the waves. Here you will find sea urchins, limpets, anemones, periwinkles, mussels, crabs, starfish, algae and so much more.
All these creatures affect the rock they live on; some scape the surface while grazing on marine algae, eroding tiny bits of rock in the process, others bore holes into the rock and live in rock burrows, grinding or dissolving the rock to make their protective shelters and generating very fine rock dust which forms mud. While each one has very little effect, together they form pits and hollows which get deeper and wider over time. This makes the limestone weaker, so when storms arrive, waves and any rocks they throw around can break off chunks of the weakened rock. Once the storm has passed, the creatures begin again, boring, scraping and dissolving for food and protection. The erosional holes and hollows they make in the rock are known as ‘biokarst’.
Studies from the northern Clare coast have estimated that sea urchins and boring bivalves can remove up to about 1cm of limestone each year to form the rounded pits they live in. That is one metre in one hundred years. This is all part of the rock cycle whereby rocks and fossils that formed over 300 million years ago are being recycled into the sea as fine mud.
The wooden ships of the Spanish Armada in 1588 are thought to have been infested by wood-boring bivalve molluscs. This would have weakened the hulls and made them more susceptible to breaking up when they struck the bored and burrowed rocky Irish west coast.
Ignore the little guys at your peril!
Dr. Eamon Doyle, geologist for the Burren and Cliffs of Moher UNESCO Global Geopark.