Limpets move slowly in a world that changes quickly at every moment. During baking sun and little water at low tide twice a day, limpets retreat to the same small beds, which they have scraped away in the rock. To find their resting spots, they follow the path where they have scraped away algae, much like lawn mower tracks. There they wait, tightly sealed from danger, as people like my daughter and I search the world revealed by the retreating tide.
Then, when the tide comes back in and the cool, constantly flowing water covers them once more, they can go back out on their algae-eating quest. They can move a few inches an hour, but I wonder how they know that the waves are going out once again. How do they know when to move back to safety?
I wish that I'd had the great Lone Pine Field Guide, Seashore Northern & Central California, along with me as my daughter and I searched low-tide Monterey a few weeks ago. It offers very clear illustrations and descriptions to distinguish the five or six common limpet species. Now looking only at photos, I believe the limpets pictured above and below are file limpets. They have a low profile, a lack of keyhole in the middle, and fine ribbing.
The keys to any limpet quest (whether for keyhole limpets or file limpets!) are to find a rocky shore and go at low tide. The field guide above suggests a great idea for observation, especially with kids. Compare how large and rounded limpets are that live on the sheltered side of a large rock (such as the bottom or where it overhangs the ground) vs. the side of the rock most facing the waves. Similar to coastal, windswept trees, the limpets that deal with more waves will most likely be flatter and smaller. The limpets I photographed were in the shadow of a very large rock (about half the size of a car) and partially protected by it. The largest one did seem at least 1.75 inches, the maximum listed in the field guide. Doing this type of comparison is a great way to get kids thinking about how waves affect the seashore habitat.
For more on limpets, especially for kids, please see my Limpets page within the tide pool section of this website.
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