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Dive Dry with Dr. Bill

#681: Why Don't You Clam Up?

There was a time not long ago when I was a very deep fellow. No, I'm not referring to the intense philosophical discussions with my classmates during my years at Harvard. Nor am I thinking of the years I spent researching for my PhD at UC Santa Barbara. I could be referring to the deep discussions with other Avalonians while sitting on the serpentine wall.

But actually my "deepness" relates to my diving of not long ago. One day at Sea Fan Grotto dive instructor Tim Mitchell returned from a dive to retrieve the King Neptune's anchor. His face was white as he approached me and he held out his dive computer which read a maximum depth of 197 feet! He said he was narced as could be.

Soon after that I began an experiment that could have ended in disaster. I gradually extended my maximum depth over a period of two months until I reached 200 feet. I was shocked to find that I was not seriously narced at that depth despite a partial pressure of oxygen of nearly 1.50 (vs 0.21 at the surface)! Back then I attributed my relative clear-headedness to the fact I was doing 300-350 dives a year and my body had likely acclimated to high levels of nitrogen.

For about two years I continued diving to such depths, which are easy to reach in Catalina waters due to the often very steep submarine slope. I decided I would use these dives to obtain footage for a proposed episode of my cable TV show on "deep ecology." While diving to these depths, I "discovered" many species I don't see in recreational diving depths (down to 130 ft).

One critter frequently encountered "down under" was a species of pholad or piddock clam. I would see its feeding siphons extending above the muddy bottom, but I had to sneak up slowly to get any decent footage. Even then it would usually withdraw its siphons into the substrate and hide from my prying camera. It just clammed up. I had no hope of digging one out to try to identify which species it was.

Like many clams, piddocks bury into soft substrate to avoid predators. They use their shells and "foot" to wiggle into the sand, mud or silt. Of course by hiding they also limit themselves at the other end of the food chain. They may avoid munchers, but still need something to munch on themselves.

Burrowing clams have solved this eternal dilemma by using a pair of fleshy tubes or siphons. One siphon takes in water, which hopefully contains not only delicious food but also life giving oxygen. After filtering out these two critical components, and releasing waste products into the internal "current," the water flows out through the second siphon.

Reproduction in piddocks and other bivalves is not generally considered very sexy except perhaps by the most obsessed of malacologists (those who study molluscs). Like many other invertebrates it reproduces by broadcast spawning, releasing eggs and sperm into the surrounding water thus taking a chance they will fertilize and develop. Fortunately, although the odds of this are not high they are better than my winning the lottery. After all, it only takes two of the little ones to replace Mom and Dad.

At times I long to return to this deep, darker world but in the last few years I've become quite a shallow fellow. There certainly were a number of very interesting species down there. However, I have granddaughters to consider. Some day I hope to grow up and see them as young adults!

© 2016 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Piddock clams with siphons extended above the bottom (top); siphons being withdrawn as I film and voila... clammed up!

This document maintained by Dr. Bill Bushing.
Material and images © 2015 Star Thrower Educational Multimedia