Star Thrower Educational Multimedia (S.T.E.M.) Dive Dry Column

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Dive Dry with Dr. Bill

#140: A Shrimp of an Abalone

For the past few weeks I've lingered on my experiences diving in the Florida Keys. I think it is finally time to come back to reality. Of course Catalina Island is a pretty good "reality" to return to! Wonder why others often refer to all that hustle and bustle on that "Big Island" we see when the smog clears as the "real" world?

The winter months usually offer some of our best diving. Colder waters and less sunlight usually prevent much plankton growth, and we experience our clearest waters. Conditions have not been great this winter and early spring, due in part to the heavy rains, occasional strong winds and sunny periods which trigger plankton blooms. Diving last weekend was like being in a washing machine. In fact, towards the end of my dives I simply turned on the video camera and let it record my surroundings as the surge spun me around. During days like this, I tend to explore the little finger reefs coming off the Casino groin (breakwater) since they provide some protection from surge and strong currents when they develop.

While combing through the shallows, I discovered a large abalone crawling out in the open well away from the protection of the breakwater rocks. I thought this was pretty strange since it was moving on top of smaller cobbles instead of larger rocks. I decided this was an excellent opportunity to film its underside, and gently turned it over taking precautions not to injure its sensitive skin. Injured abalone can perish easily, and we need every individual we can get to fulfill their primary function of reproducing... so I can once again eat a wild one in my lifetime.

This abalone must have been a member of the Screen Actor's Guild. It performed an impressive series of gyrations in an attempt to turn itself over. This made for great footage of course. I did notice that it had a wound on the side of its massive foot. I wondered what might have caused this. It almost looked like the mark a makeshift "ab iron" might cause if someone tried to remove it. I wondered if this was the reason it was out in the open rather than in some well protected nook or cranny.

I filmed the foot of this magnificent mollusc. It was almost like filming a beautiful model... I kept having these shameful thoughts (of munching, not mating). In this case my mind was distracted by how beautiful this foot would look sliced and breaded on my dinner plate! Of course as an avid conservationist I did not let such thoughts get the better of me. I remained admirably focused on more altruistic thoughts of filming this critter so I could produce underwater films educating others as to the need for its conservation rather than my own self gratification. Besides, I misplaced my abalone mallet decades ago.

As I filmed, an old friend suddenly appeared from under the abalone's mantle. Here was a marine creature I hadn't seen in a decade or more... an abalone shrimp! Years ago I used to find them in the abalone I harvested in the "good old days" before over-harvesting and withering foot syndrome effectively wiped them out. These inch long, dark reddish-purple shrimps live inside the shell of abalone in the cavity beneath the fleshy foot and mantle. They look almost like miniature Maine lobster (and some of my students used to think they were). I was amazed to find almost nothing in my marine biology books or the Internet on this species.

The pioneer West Coast husband and wife marine biologists G. E. and Nettie MacGinitie experimented with these shrimp and their abalone hosts. They placed twenty abalone shrimp in a tank with two live abalone. Initially all of the shrimp sheltered within the shells of the two abalone, but after a while only one shrimp resided in each abalone. I guess they modified that old line from B-westerns... "this shell ain't big enough for the both of us!" In the "wild" it is rare to find more than one shrimp in a single abalone. For that matter it is rare to find an abalone itself!

These shrimp are rarely seen in the open, preferring the protection afforded by the abalone's shell. Apparently its presence does not directly affect the abalone (although occasionally an abalone will lift its shell to let its little "house mate" inside). A species which gains a benefit from another species without harming it is known as a commensal organism. A closely related species, the urchin shrimp, lives underneath the protective spines of red and purple sea urchins. Other species are known to inhabit the burrows of ghost shrimp and echiurid worms. There are even shrimps and crabs that live within the anal cavities of sea cucumbers and other marine life. I assume the rent must be pretty cheap to accept such accommodations! Oops, that's right... the host animal doesn't gain any benefit so all these animals must live rent free!

After I finished filming it, I carefully placed the abalone into a well-hidden rock crevice so it would not end up on someone's dinner plate. Shortly afterwards I found another large abalone in a relatively unprotected area close by and wondered why. The following day I did not see any abalone out in the open, just two other individuals that were safe in their hiding places (and therefore difficult to film). When I reached the area where I had seen the two large abalone the previous day, I found a newly emptied shell sitting on the bottom. I filmed it to record the muscle scar on the shell's interior, and then looked at it more carefully. It appeared to be from the abalone I had filmed the day before. Hmmm? It appeared to have died, possibly due to the prior injury, and been consumed by natural predators, rather than poached by humans since there were no scratch marks on the inside of the shell. One less abalone to contribute to the recovery gene pool.

Carefully overturned abalone; abalone attempting to turn itself back over;
image (and close-up) of abalone shrimp before it scurried under the mantle.