Dive Dry with Dr. Bill

110: Scallop Stumps Scripps Scientists

Just when you thought you'd seen it all, something unexpected pops up. After not diving while in Florida, I was anxious to get wet here at home. I donned my gear and dove out to the old "swim platform" (actually one of the old boat floats according to Lorraine Sadler who helped bring it into the Park) in the north corner. I don't go there very often in summer because the hoards of open water (OW) beginning SCUBA classes tend to stir up the bottom in that area, making it difficult to see or videotape. On this day I was early enough to avoid the crowds.

I discovered a small octopus resting in its burrow in the sandy bottom and filmed it. As I swam away, I noticed what at first looked like abalone "tentacles" extending from the side of a seaweed-covered rock nearby. Upon closer inspection, I discovered that it was not an abalone, but a giant scallop. And this was a species I had never seen before. Those of us who love to eat scallops recognize members of the group easily. Those of us who buy gas on the mainland are familiar with the scallop shell that serves as the logo for Shell Oil (a brand we don't have in our one gas station town here).

This scallop was almost large enough to be made into a sign for a gas station. It is the size of my extended hand, about 8-9 inches. It was not attached to a rock like the rock scallops most divers in southern California are familiar with. This was an epibenthic scallop. For those of you who don't understand high falutin' scientific lingo, that means an animal that lives on top of the bottom (hmmm, that sounds even more confusing). Like their relatives the clams, mussels and oysters; scallops are "bivalves" meaning they have two shells. Neither of these scallop's shells is attached to the bottom. The lower shell merely rests on the bottom, and the upper shell gets covered with algae and encrusting forms that create a natural camouflage. That is why I thought it was just another rock.

Although some bivalves like clams burrow into the sand, this one apparently didn't. If it did, the upper shell would not develop algal growth because the seaweed couldn't grow under the sand where there is no light. Some scallops are known to escape predators like starfish by flapping their shells (valves) and swimming away. I think this species was far too big and too heavy to escape from a predator that way, however they say bumblebees aren't supposed to fly but they do. Like other bivalves, scallops filter feed by pumping water into the cavity inside the shells and extracting food with modified gills. Given its location I would expect this scallop might need a toothpick to remove all the sand and grit stirred up by the new divers.

Since this giant scallop appeared to be all alone, I worried about its sex life (a topic I haven't brought up recently in case you didn't notice). Remember, life is about more than just munching... mating is equally important for the survival of the species. Without a mate in sight, it could be a very lonely life. Believe me, I know! Then, in researching this article, I discovered that some scallops are hermaphrodites... that is, they possess BOTH male and female organs. Remember the nudibranchs I wrote about earlier? They are hermaphrodites too and use the "Wrigley Doublemint" philosophy when mating- double your pleasure, double your fun! I guess if no mate appears in the Park, this scallop can always succeed by becoming autoerotic. Doesn't sound like much fun to me.

Although starfish are one natural predator on the smaller scallops and rock scallops, it would probably take more strength than most starfish possess to open the valves of this giant. I would assume that by the time they reach this size, there are few predators they have to worry about other than man. I used to love eating other bivalves like mussels and clams. Then Jean-Michel Cousteau cautioned me never to eat animals which filter their food from the water, or filtering organs in animals such as the liver, because they tend to concentrate toxins. Giving up liver was easy... clams and mussels was much harder. However, when scallops are eaten, it is usually the strong adductor muscle that holds the two valves or shells closed rather than the body itself that is consumed. Since the muscle (as opposed to mussel) doesn't concentrate the toxins, scallops and rock scallops are much safer to eat. I had a nice plate of them for dinner in Florida.

I didn't want to collect this unusual scallop since it was the only one I'd ever seen in our waters. I took plenty of video and extracted still images like the ones here to send to experts for possible identification. A friend of mine forwarded the pictures to two experts at Scripps Institution of Oceanography in La Jolla. So far they are stumped as to what this critter might be. So am I. Just goes to show, it can take a lifetime or two to know "everything" within even the most familiar ecosystems. That is part of what keeps me diving as often as I do. In this life, and hopefully the next!

© 2004 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.

Upper shell of giant scallop imitating a seaweed-covered rock, the lower shell free from growth,
the giant scallop and my giant hand for comparison, the tentacle-like fringe of the
animal's body extending out from between the two shells.

This document maintained by Dr. Bill Bushing.
Material © 2004 Star Thrower Educational Multimedia