This corresponds closely to what I observed. It was at Cumberland Island
National Seashore in mid-March. The thin hair-like brown algal growth was
visible on the surface of the sand.  This is a clean sand beach with very
shallow slope for those not familiar with the site.  It is located just
north of the Florida/Georgia border.
 
I live in Maine and only get to travel to places like this in conjunction
with biannual conferences which I attend as part of my work so any
additional investigation will have to be done by someone else.  I am
guessing (theorizing if you're a scientist) that the algal growth benefit
the D. variabilis by catching tiny protozoa, ect in the seawater which the
clam's siphon then pulls in (The Leaf Rake Theory) but I don't know and I'm
not sure how you would test a theory like that.
 
Beth DeHaas (My husband is Peter Froehlich but he doesn't collect shells)
[log in to unmask]
 
 
----------
> From: CLloyd6888 <[log in to unmask]>
> To: [log in to unmask]
> Subject: Re: Donax variabilis
> Date: Wednesday, March 04, 1998 5:36 PM
>
> Dear Art,
> I'm sending this message to you since I deleted Peter Froehlich's message
> about Donax variabilis by mistake after reading it.
>
> I have also observed Donax variabilis with some type of growth on them.
It is
> usually seen during the summer months and will involve large populations
of
> Donax found on local beaches here in Northeast Florida.  The Donax that I
saw
> with these growths were all alive.  I'll describe the growth attachments
as
> best I can.  They were allways located at the posterior end of the Donax.
> They were  yellow-brown in color and seemed to be thin hair-like
structures up
> to 1 inch in length.  They were quite thick and spread out in the water
when
> the Donax tries to burrow into the sand.  As a matter of fact, the
growths did
> inhibit the Donax from burrowing effectively.  On many occasions the
Donax
> would be just under the sand with the growth protruding up into the
water.  In
> some Donax populations along our beach at least 50% of the animals would
have
> these seasonal growths.  I had always assumed that it was some sort of
> attached colonial hydroid.  I guess I'll just have to collect some this
summer
> and get out the identification books to find out what type of growth it
is.
> Sincerely,
> Charlotte Lloyd