What tells periwinkles to climb? You can create several different hypotheses to examine the behavior of these organisms. Periwinkles are very easy to keep in the classroom. You can do some simple experiments with them to illustrate their adaptations to living at the edge.
The periwinkles move up and down objects as the tide changes. To test whether they move because of water covering them or because of some internal clock, you can do the following. Find a tide chart for the area; you can also pick up a local tide table from most fishing tackle shops). Look to see when high and low tides occur. Place the animals in a bowl and observe what they do. Record your observations. This takes some planning in our area because of the type of cycle that we have, so be sure to look at the tables in advance to have the experiments during class time. Sometimes when encountering a new environment, the animals climb. So, it is best to make your observations a day after you first place them into their container. This allows the animals to acclimate (adjust) to their conditions. Place some carrot slivers and some dry fish flavor cat food in the bottom near the winkles. If there is an internal clock related to tide, you should be able to see them climb for "high" tide and come to the bottom to feed during "low" tide. You may have to take a few days to a couple of weeks to get the observations at the different tide times.
If the animals react to water, you should be able to change their behaviors quickly. In the bowl with some periwinkles, tilt the bowl and place about a cup of seawater in it. Slowly right the bowl until the winkles are covered with water. What do they do? Tilt the bowl again to uncover the winkles. Does their behavior change? If it does change, how long does it take for them to move? Be sure to check the tides if your previous experiment showed that they move up and down with the tides.
You can buy a frozen blue crab from the grocery store. Blue crabs (Callinectes sapidus) are major predators of periwinkles. During high tide, they can be seen shaking Spartina to dislodge periwinkles or pushing over the grass to remove the winkles. Remove a leg from the crab carcass and allow it to thaw in a small container of seawater. You are creating "essence of predator" that you can use in the following experiment.
Now that you have observed whether the periwinkles climb with you cover them with water, you can determine if their rate of climbing might be affected by the presence of a predator. The essence of predator that you have created can be used instead of a live predator. This suggests that the periwinkles smell their predators before they see them (Is this a reasonable guess? What do you think?) Add several drops of your crab essence to the test bowl and tilt it to cover the periwinkles with the water. Time them to see if they move faster with the essence in the water than they did with just the water in the previous experiment.
Do periwinkles have a preference for objects that they climb?
Perhaps periwinkles will climb particular objects if given an opportunity?
Periwinkles can be maintained in the lab for several weeks with little special equipment. As with all animals, however, please return them to their native habitats as soon as possible.
Get a clear container and fill it with about 4 cm of beach sand or mixed beach and play sand. Add enough seawater to the container to cover the sand by a cm. Tilt the container so that some of the sand is dry. Place algae covered rocks in the container. If you have a dock, you can suspend tiles or pieces of rock to collect algae so that you can have a fresh supply for the snails on a regular basis.
Periwinkles are grazers, ingesting plant material along with bacteria. Occasionally, they will also eat meat. To maintain the animals in the laboratory, it is necessary to supply rocks covered with algae. They will also eat small slivers of carrot and other vegetables. You can try a variety, but do not leave food in the container for more than a day.
You must have an area in the container that is only partially covered with water. If the container is completely filled, the snails will climb to the top and remain there. After you have the container set up, place the snails into the container at the edge of the water and near the rocks. Some will climb the sides of the container while others may climb on the rocks. Be sure to put a lid on the top of the container so that the snails do not climb out. Once every two to three days, spray the container with spring water to simulate rain. This helps to compensate for evaporation in the container. You can keep the container in an area that gets partial sun exposure, but do not keep in full sunlight. When the animals get too hot, they secrete a mucous plug and do not feed.
Background readings for Littorina experiments
Here are a few references that might be of use. Students in grades 9-12 should be able to read these papers and understand the information.
Chandrasekara and Frid, 1998. A laboratory assessment of the survival and vertical movement of two epibenthic gastropod species, Hydrobia ulvae (Pennant) and Littorina littorea (Linnaeus), after burial in sediment, Journal of Experimental Marine Biology and Ecology 221 (2): 191-207.
Duval, Calzetta, and Rittschof. 1994. Behavioral responses of Littorina irrorata (Say) to water-borne odors. Journal of Chemical Ecology, 20: 3321-3334.
Hamilton, 1982. Behavioral responses to visual stimuli by the snail, Littorina irrorata. Animal Behaviour, 30: 752-760.
Keppel and Scrosati, 2004. Chemically mediated avoidance of Hemigrapsus nudus (Crustacea) by Littorina scutulata (Gastropoda): effects of species coexistence and variable cues. Animal Behaviour, 68: 915-920.
Remy and Dill, 2000. Mortality, behavior and the effects of predators on the intertidal distribution of littorinid gastropods, Journal of Experimental Marine Biology and Ecology 253 (2): 165-191.
Yamada, Navarrete and Needham, 1998. Predation induced changes in behavior and growth rate in three populations of the intertidal snail, Littorina sitkana (Philippi). Journal of Experimental Marine Biology and Ecology 220:213-226.
Next: Fiddler crabs