Naturespeak A naturalist's view of the world

October 3, 2009

A Clam in Time Saves Nine

Filed under: Uncategorized — wykes @ 3:49 pm

I was walking the shoreline east of Port Clinton, Ohio last week and saw that the wind had created an extensive wind tide. This  effect, called a seiche (a Norwegian word I believe), involves a bit of bathtub science in which the lake basin acts like a tub of water being tipped by a prolonged western wind. A wall of water is pushed toward Buffalo and the western shore is left waterless. Winds up to 50 mph had exposed at least an 1/8 mile of open sand flats extending from the rock-covered shore to the harbor break walls (see here). The water level dropped by 8 feet in some places along the shallow basin of western Lake Erie. For some the phenomenon posed a temporary irritation but for others it posed a deadly trial. Totally aquatic beasts, such as fish, clams, and water plants are put to the hardest test. Open wind-exposed sand is hardly conducive to maintaining a wet life.

The sand substrate in the near-shore environment offers little even on the best of days. This habitat consists of a continually shifting bottom habitat. Only a few patches of water celery and a few scattered boulders provided any stationary cover. Nutrient rich waters make this place worth whatever effort is expended here. One of the tougher inhabitants of this zone – at least in this particular place – were large native calms (aka mussels) known as Floaters. Contrary to their name, however, they don’t float or even tread water. They pretty much remain in place on the bottom until prompted to move by hunger or boredom.  I came upon quite a few of these creatures out on the flats. All were attempting to dig down into the substrate to avoid the dangerous bout of dryness thrust upon them. Their efforts created winding trails carved into the hardening sand. Each trail ended in a partially entrenched clam (see here & below).

The problem is that mussels don’t move very fast. “Glacial” would be a good way to describe their pacing. When they do move they do so using a large white muscular foot that extends out and swells much like an anchor. The heavy mollusk pulls itself forward to the anchor point and repeats the process. A clam journey is measured in inches rather than feet. (You can see this foot sticking out along the lower right edge of the shell in the view below). Since they have the reaction time of a refrigerated snail, they can’t respond quickly to the lowering water brought about by a seiche. By the time they are thinking “hey, the water is going away- I’d better dig in…,” the water is already gone and they are forced to deal with hard-packed sand.

If they can bury themselves properly, they can survive for quite a while on the water entrapped within the tight lips of their mantle folds. Most of the clams I found were well on their way to security.

Unfortunately, one of the nasty realities in these parts are the colonies of Zebra Mussels that infest nearly every clam (see here and below). Zebras need a hard surface in order to carry out their devious plans to take over the earth. Out in the sand shallows, the protruding portion of the native Floaters provides a dandy place to set up shop. These colonies can get so large that they will literally rob their host of food and eventually kill them. One of the most disastrous long term effects brought about by Zebra Mussels is that they are reducing our native Clam population.

Every Floater I encountered was encrusted with Zebra Mussels. One very large individual (see above) was not yet totally buried so I decided to  scrape away every zebra I could as a small act of kindness. Life is tough enough without this extra added burden. This job was not an easy task given that the mussels were individually attached to the shell and each other via strong byssal anchor threads. Once the job was completed I ended up with a pile of over 100 zebra shells laying on the sand next to their former host (see here).

The zebra-less Floater probably didn’t even realize that she was lighter until long after her life-giving water had returned. This clam did not look at me with soft eyes and say “thanks” as I repositioned it deep in the sand. Since she has no eyes and only a quarter of a brain to render such an emotion, this is no surprise. But maybe, just maybe, this one will survive long enough to produce at least nine more clammlets in the future. This provided me a small measure of comfort out there on that cold Lake Erie sand flat.

1 Comment »

  1. Fascinating. I as just thinking to myself “are those zebra mussels on the clam?” when your next paragraph answered me! Nasty things. Glad you helped at least one clam with its extra burden. Excellent post.

    Comment by Ellen — October 7, 2009 @ 12:52 pm

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