Figure 1In Fig. 1 the snails were purposely placed on the white quartz substrate to show the contrast between a shell of color 27 ( white ) and some of colors 1 - 10 ( Black to grey ).
Patterns of Color Polymorphism in the Intertidal Snail Littorina sitkana in the Race Rocks Marine Protected Area.
Extended Essay done by: Giovanni Rosso, Lester Pearson College, 1998 .
The complete version of the research is available in the Library at the college.
Abstract:
As with most intertidal gastropods, Littorina sitkana shows remarkable variations in shell color. This occurs both in microhabitats which are exposed or sheltered from wave action. There seemed to be a close link between the shell coloration of the periwinkle and the color of the background substrate. Field work was carried out on the Race Rocks Marine Protected Area in order to investigate patterns of color polymorphism. Evidence from previous studies was used to support interpretations and understand certain behaviors.
The results showed that in the study site there was a very strong relation between the shades of the shells and the colors of the rocks. Light colored shells stayed on light shaded rocks and vice versa. An interesting pattern was noticed with the white morphs. These were rare along the coast
(only 2%), but were present in relatively high numbers in tidepools of white quartz. From previous experience (Ron J.Etter,1988), these morphs seem to have developed as evolutionary response a higher resistance to physiological stress from drastic temperature changes between tides. Some results showed that the white morph is present in an unexpectedly high percentage at the juvenile stage, but then their number decreases dramatically. As in Etter's study more research needs to be made on the role visual predators have in this phenomenon.
Figure 1
In Fig. 1 the snails were purposely placed on the white quartz substrate to show the contrast between a shell of color 27 ( white ) and some of colors 1 - 10 ( Black to grey ).
Figure 2
In Figure 3. Several colors of snail can be seen grazing on the golden diatoms in Pool 4 in the spring of 1998.
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