Dive Dry with Dr. Bill

#281: The Wavy Top Snail

It's hard to believe that the first Earth Day was 38 years ago on April 22, 1970. I was involved in some of the regional planning for that event, and remember teaching my students at the old Toyon School that day about environmental issues ranging from the depletion of our kelp forests due to sewage pollution, to the use of non-recyclable packaging and our solid waste issues on the island, to the use of Agent Orange as a defoliant in Vietnam. Many of the concerns raised back in those early days of the environmental movement are now coming home to roost as major problems that are finally being faced by our own Avalon and the rest of the country.

Today I focus more on Planet Ocean than the measly 30% that is "earth," but I learned most of the scientific names of our local marine critters back in that same era when I first started diving Catalina and teaching marine biology here. Many of these scientific names have changed since that ancient time, and I must admit I haven't always kept up with these changes. Heck, by the time I learn the new Latin name, there will be a newer Latin name for the same critter... and absolutely nothing about that species has changed other than the names we've given it!

The species I'll write about today is one of them. I initially encountered it on my first dive at Arrow Point back on August 24, 1969. Back then I learned the wavy top snail's scientific name as Astraea undosa. I also encountered it many times during a "salvage dig" at the Isthmus that fall. The SCICo had given us two weeks to complete an archaeological dig there before they broke ground for a new hotel at Two Harbors early in 1970. Our Native Americans ate a lot of these gargantuan escargot so there were piles of them in their middens. Of course I'm still waiting to see that new hotel, but it's nice to know some things don't change.

The wavy top is now known as Lithopoma undosum, but I almost never remember to use that name. This snail is known from Point Conception to Isla Asuncion, Baja California. It is usually found on rocks in kelp beds from the low intertidal to a depth of about 70 feet. The thick calcium carbonate shell is sculpted and has spiral cords near the base. The snail seals it up tight with a thick operculum or trap door to prevent predators from getting to the animal's soft parts. The shell may reach a diameter of 4 1/2 inches. It often has a brown fuzzy covering on the outside which is known as the periostracum. Memorize that word... there will be a test next month... and I'm not referring to a sea urchin test!

According to one of the primary field guides to our region, little is known about this very common snail. Unfortunately this is too often the case with a common species that has little economic value. Scientists often like to study the rare and unique species instead of the common ones, which usually are the ones that exert the greatest influence in our local ecological systems. My marine biologist icon Edward F. "Doc" Ricketts of Cannery Row fame realized this many years ago as he was preparing to write his classic 1939 book Between Pacific Tides which I first used at Harvard and then as one of my textbooks in my classes at Toyon.

In fact my book and Internet research for this column had nothing to say about its munching or mating. We do know that it feeds by scraping algae off rocks and is therefore an herbivore. It must keep its sex life very secretive if no one has written about it... and I have yet to film it. My readers will just have to fantasize about it. One thing I feel fairly comfortable writing... it probably proceeds at a snail's pace!

I have made two interesting observations about the role of this large snail in our kelp forests. The first is that a lot of algae and encrusting invertebrates like to attach to the thick shell, probably thinking it is just a rock. This gives the snail camouflage to add to the thick shell as a defense against predators like the knobby sea star. I have seen our own giant kelp and even the non-native Asian kelp, Sargassum filicinum, attach to the shell. However, these two kelp species may grow substantially, creating a lot of drag for the poor snail. If the giant kelp grows too big, it may actually lift the snail shell off the bottom and send it adrift.

The second observation is a relationship the snail, or at least its shell, has with our local two-spotted octopus. Now I wouldn't be surprised if the octopus often feasts upon this delectable snail. If it can get past the thick shell and operculum, there's a lot of meat for one meal. However, what I see that truly amuses me is many octopuses using the shell of this snail to plug up their holes in the rock reef. The octopus will grab the shell, usually with the tapering part towards its hole, and pull it in until it forms a nice defensive barrier to keep predatory fish away. But then I've also heard reports that the octopus will use an empty beer can to do the same thing. Gives new meaning to "It's Miller time!"

© 2008 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass," "Common Fish and Invertebrates of the Sea of Cortez" or the new "Sharks and Rays of Southern California" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

Wavy top snails on a rock, the shell seen from the side; the operculum or trap door,
and an octopus using a wavy top snail to seal its hole

This document maintained by Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia