I enjoy all of the positive and lighthearted messages that I receive from
Conch-L, and (I admit) I even enjoy some of the negative comments, if they
are witty. But I am a paleoecologist at heart, and some of my favorite
messages have to do with observations on natural history. It is easier to
amass a large collection of perfect shells than to gather a large mass of
accurate notes on molluscan behavior. No one person can be everywhere and
see everything in a mere lifetime. This is one of the many areas of
malacology where the avocational wing can make a big contribution.
 
Peter Froehlich's notes on Donax variabilis with attached algae make a good
example. Here, he brings our attention to an observation (algae on Donax
variabilis), but is not content simply to report the fact. He confronts
this fact with a well-known bit of lore (Donax moves up and down the beach
during the tidal cycle) to ask a reasonable question: Can Donax still move
effectively after it has been colonized by algae?
 
This is a good, solid question about an abundant species that is widespread
on southeastern U.S. shores. The answer will be of interest to a lot of
Conchlers, and not just the Americans. Unless I am mistaken, it does not
have a simple or immediate answer. Someone will have to investigate the
Donax in its native beaches.
 
The migration question might be hard to track, but a more modest approach
would not be difficult. Those of us who have seen Donax variabilis know
that this bivalve burrows rapidly into sand after being placed on the
surface. OK, the trick is to find a beach that has some specimens coated
with algae and some not. Take individual specimens of Donax (which are
brightly colored in many hues, so it should be easy to distinguish them).
Put them on the sand and time how fast it takes for them to burrow
completely into the sand, beginning with the first sign of movement. Do
this several times with different specimens. It will definitely help if you
have one person to handle the wet clams and another person with clean hands
to measure and record the time.
 
Recommended: If possible, also measure and record the temperature at the
same place (not higher up on the beach, which of course may be much
warmer). It is known that burrowing rates of bivalves tend to be more rapid
at higher temperatures (see Geerat Vermeij's book on the natural history of
shells), but we don't know very much about it. If you measure all of the
specimens under the same conditions, so the temperature is the same for all
of them, then temperature won't affect the results.
 
I hope that one of you Conchlers takes up the challenge to see how athletic
Donax variabilis can be with an algal handicap. Of course, the algae may be
seasonal, and it may be summer before anyone can do this. Peter, what time
of year did you make your original observation? Which island? And was it on
an ordinary beach, or one that was close to a tidal inlet or had other
unusual features?
 
The results could also make an unusual and very intriguing exhibit at a
shell show.
 
Andrew K. Rindsberg
Geological Survey of Alabama