Question:
Do Littorina snails move significantly due to tidal cycles?
Methods:
The experiment was conducted in two trials during October and November of 2008 in Nahant, MA, USA. The intertidal zone here is predominantly Ascophyllum based along with Fucus species. There is an extremely large population of Littorina sp. in this location, mainly L. obtusada, L. littorea, and L. saxatilis. The experiment was conducted in two trials during October and November of 2008. There were two phases to the experiment, Phase 1 involved the tagging of snails and Phase 2 consisted of survey for the marked snails. For Phase 1, a 1m2 quadrat was randomly placed within the middle intertidal zone. 30 Littorina snails were then marked using metallic waterproof nail polish. This was done in two batches, pink and blue, at different locations. This process was repeated for the second round of trials. Trial 1 lasted 10 days or 21 tidal cycles and Trial 2 lasted 3 days or 7 tidal cycles. At this point the area surrounding the quadrat was surveyed in a 5m radius for any marked snails.
Results:
Trial 1 lasted 10 days and only 2 snails were found from one group. One was still within the quadrat area and one was located 2.3m away almost directly towards the water. All other 28 were outside the 5m area. None of the 30 were found from the second group inside the 5m area.
Trial 2 lasted 3 days and 3 snails were found, two from one group (A) and one from the other (B). Those from group A were located at 1.6m and 3.4m from the quadrat. The one from group B was .7m from the quadrat. Again all three snails were located in the direction of the water, nearly in a path of least resistance. All other snails were not found in the survey area.
Trial 1 | |||
Group | Tagged | Found | Distance |
A | 30 | 2 | 0m, 2.3m |
B | 30 | 0 | N/A |
Trial 2 | |||
Group | Tagged | Found | Distance |
A | 30 | 2 | 1.6m, 3.4m |
B | 30 | 1 | 0.7m |
Therefore, in Trial 1 nearly 97% of snails vacated the 5m range within 21 tidal cycles. Trial 2 saw this number drop slightly to 95% by 7 tidal cycles. Both trials saw significant movement of the vast majority of snails from their origin.
