Littorina's Lifestyles

Littorina sp., commonly known as the periwinkle snail, are abundant in the Northern Hemisphere’s temperate and subarctic regions at latitudes of roughly 80° N to 20° S (Reid, 1996). The ideal habitat provides a balance of both air and water exposure, to prevent desiccation or drowning (Griffith, 1975). For this reason, they are uncommon in the low intertidal zone where there is limited air exposure, and are predominantly found in rock pools and rocky shores in the middle and high intertidal zones instead (Moore, 1937). Large rocks in Littorina sp.’s habitat allow it to comfortably stay out of its predators’ reach (Reid, 1996). In Littorina sp.’s natural habitat, the middle and high intertidal zones, there is a lot of variation in the
moisture levels. The middle intertidal zone is alternately exposed and submerged by tides during the day, with moisture levels ranging from completely submerged substrate during high tide to slightly damp substrate during low tide. As for the high intertidal zone, due to its elevation, there is little moisture found as the tide rarely reaches this zone. Additionally, based on measurements taken at Tower Beach, the high intertidal zone experiences a much greater light intensity than the middle zone, which results in evaporation of moisture that may have remained from the tide.
We are investigating Littorina sp.’s behaviour of retracting its body into its shell and forming a tight seal between its body and the environment to deal with varying levels of moisture.
The columellar muscle is attached to its foot and is responsible for movement and retraction of its body (Chase, 2002). Littorina sp. seal the openings of their shells with a thin piece of shell on the bottom of their feet called operculum and by secreting mucus which dries and form a thin film (Wilson, 1929). This behaviour is crucial as moisture availability directly impacts all aspects of the Littorina sp.’s survival and wellbeing. For example, Littorina sp.’s ability to form a seal between its body and the environment allows it to prevent desiccation when the tide is low and causes prolonged air exposure to the substrate. Desiccation is highly problematic drying conditions on Littorina sp. causes the impairment of movement and ability to attach to substrate as a result of the structure of the snail’s foot being compromised (Clarke et al., 2000). Impaired movement leaves Littorina sp. unable to collect food sources, and more vulnerable to predation. Littorina sp.’s retracting behaviour increases its survivability, allowing it to continue to grow and
reproduce.
However, Littorina sp.’s retracting behaviour changes depending on the availability of moisture in its environment.
For example, we observed at Tower Beach that Littorina sp. completely sealed their shells in areas where water was not as plentiful. This observation is consistent with the findings of Wilson et al. (1929) who noticed that groups of Littorina sp., all with their shell openings closed, would collectively cling to the sides of boulders as close as possible to the damp substrate. This suggests that in moisture scarce conditions, Littorina sp. will exhibit their retracting behaviour to conserve water, and group together to decrease their surface area to minimize evaporation. Additionally, it was observed in an experiment conducted by Chapman et al. (1996) that Littorina sp. were more active and dispersed when their substrates were wet, giving them the opportunity to search for food in suitable conditions. This finding suggests that Littorina sp.s do not require their adaptive behaviour of remaining stationary and forming a tight seal between its body and the environment in conditions where moisture is readily available, and that they will instead take the opportunity to disperse and
forage.
The objective of our experiment is to determine how much time Littorina sp. spends retracted inside its shell depending on the availability of moisture in its environment. We predict that Littorina sp. will spend little/no time inside its shell in an environment with an abundance of moisture as it needs will be met, and that it will spend more time inside its shell where there is a lack of moisture, in attempt to stay hydrated.