New Kid On The Rocks (NKOTR)

Littorina littorea - on foot

A periwinkle

What happens when a new kid steps onto the playground? They might not be accepted into the group right away, they might be a bit of a bully and take other kids’ toys, or they might fit right in and join in the fun and games. The same is true for invasive species, that is, species that have been moved into new locations where they weren’t previously found. Generally, the introduction of a new species creates challenges for native species; they rarely fit right in.

A marine snail called the European periwinkle (Littorina littorea) was introduced to the Atlantic coast of North America and now spreads from Labrador to New Jersey. When the periwinkle showed up, it took over space that was previously used by a native species, the mud snail. Up to 70% of the space that mud snails would use is now taken up by periwinkles. Periwinkles also cause trouble by removing sediment while they graze. Sediment is a habitat favoured by marine organisms such as polychaete worms and mud crabs; these organisms suffer when their habitat is removed by periwinkles. However, the same grazing behaviour by periwinkles increases space available for barnacles and encrusting algae to grow. With these three examples, the take-home message is that the addition of a new species (or rather, a new kid on the rocks), alters the community and habitat that it is introduced to.


The future competitors. A black turban snail (left) and a periwinkle (right)

Recently, these same periwinkles were spotted on the Pacific coast of North America, but they haven’t taken over quite yet. So far, only adult individuals have been seen, which means that there probably hasn’t been any successful periwinkle reproduction yet. So, if you’re anything like me, you might be thinking to yourself, what might happen if the periwinkle population grows and it becomes a bigger part of the intertidal community in BC? In an attempt to answer that question, I looked to the black turban snail (Chlorostoma funebralis). The black turban snail is a native to BC waters and it is about the same size at the periwinkle, with similar feeding habits. And so, periwinkles will probably need to use similar resources as black turban snails, which will result in competition. The only trouble with this scenario is that periwinkles haven’t been seen in the same habitat as black turban snails, but with its introduction to Vancouver BC, we can imagine a time in the near future in which they are both living in the same community.


The experimental set-up. Snails were left in bottles to graze on algae for 48 hours.

Competition from introduced periwinkles could decrease the success of native black turban snails. To explore this, I looked at the amount of algae that each snail consumes when they are in water of different salinities. It was important to manipulate salinity because there is often heavy rainfall on the coast of BC that decreases the salinity of the water for a day or so, and these changes in salinity can affect the feeding rates of the snails.

Unfortunately, the experiment failed (which happens sometimes), so I am unable to tell you how fierce the competition might be. I was able to learn, from my other experiments, that periwinkles and black turban snails handle salinity stress in similar ways, so changes in salinity probably won’t give one snail the competitive edge over the other. At this point, the threat of a periwinkle invasion exists, but its effects on native communities in BC remains unknown.


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