If you were a 2.5 cm tall snail, would you be afraid if alerted to the presence of a 20 cm long, unfamiliar predator? Well, if I were the snail, I think I would! The project that I conducted over the past few weeks points to the contrary; the Littorina littorea sea snails, also known as the Common Periwinkle, that I exposed to the presence of a large and potentially predatory Dungeness crab did not seem to show a tendency to look for places to hide, a curious result.
Sea snails often show a common response to predators – they move upwards and outwards away from the potential danger! For my project I looked at a different response; do they move towards rocks to find refuge from the chemical presence of the Dungeness crab?
In order to assess if the sea snails were looking for hiding places in the presence of chemicals from the Dungeness crab, I looked at how much they ate in the hiding places provided in my experiment; the more algae, one of their favourite food, they ate in the hiding places, or rocks, the more time I assumed they spent hiding. The feeding action of the Common Periwinkle when eating algae is a very interesting one. They have a tongue-like structure called the radula in their mouths. The radula has tooth-like projections that allow them to grind off algae for consumption.
After leaving the snails in water with Dungeness crab chemicals for four days, I recorded my data and then looked at my results. Like I mentioned before, I didn’t find that they spent more time hiding in the presence of the predatory Dungeness crab chemicals. Why would that be? It seems logical that they would try and hide from a potential predator. Well, there are number of things that could be responsible for this result. Maybe the escape response of the snails to this crab is primarily the action of crawling out of the water, not looking for rocks to hide under. Another response could be the snails hiding in their own shells! Common Periwinkles have a special structure called the operculum. The operculum acts like a swinging gate that can close shut when they need it to escape danger. Lastly, it may also have to do with the predator. Dungeness crabs live in the Pacific, while Common Periwinkles are from the Atlantic. It could just be that they don’t recognize the scent of the Dungeness crab as an alert that a predator may be nearby! Regardless, the interactions and responses between species in our oceans are complex and they are definitely always interesting!
To learn about the interesting account of the Common Periwinkle in North America take a look at this link: http://www.exoticsguide.org/littorina_littorea