Did you guess correctly?
This is the Little Blue Periwinkle, a remarkable snail which lives attached to rocks at the top of the intertidal zone. Have you wondered what would it be like to live here?
Our beaches experience two high and two low tides a day which creates a constantly changing environment. At low tide, the snails will be out of the water and the higher up the beach they are, the more time they spend out of the water, the lower down the beach the less time.
The falling tide exposes snails to the air which creates several problems. The first is breathing. All snails extract oxygen from the water using gills, so when they are out of the water their access to oxygen is greatly reduced. To manage this, the Little Blue Periwinkle can lower its body’s metabolism and in doing so, reduce its demand for oxygen.
The next problem is the temperature. The body temperature of a snail is linked to its surroundings. So, on a summer’s day in Melbourne when the water temperature is 20oC and the air temperature is 40oC, as the tide falls, our snails’ body temperature will increase from 20oC to 40oC then continue to increase as it is baked by the sun. To reduce these temperature changes the Little Blue Periwinkle will move to a location where it can minimize the time spent in direct sunlight.
As the temperature increases, evaporation also increases, which means the snails are constantly losing water. While the Little Blue Periwinkles can survive losing up to 70% of their water content, their waterproof shell and a mucous they produce to seal the opening of their shell helps to reduce evaporation. They can also store water inside their shells to help them survive. The Little Blue Periwinkles will cluster together creating a humid microclimate further reducing water loss.
Lastly, these snails are herbivores, they graze on the lichens and microscopic algae that coat the surfaces on which they live. They can only feed when you are submerged, so mealtimes are limited to when they are underwater. When we walk around on a rock platform the snails appear to be stationary. Watch this 30-minute time-lapse taken at Flinders Beach to see what is really going on beneath our feet.
While we have focused on the Little Blue Periwinkle, the problems of living in the intertidal zone are faced by all inhabitants of the zone. They are a remarkable group of animals living in such a tough environment. Next time you are at the beach and take a swim to cool down, spare a thought for the snails that must remain on the rocks.
If you would like to learn more about the fascinating world of the Little Blue Periwinkle and the huge diversity of life that can be found in your local rock pools, please contact Education Director Mandy Robertson on firstname.lastname@example.org