Andrew Grebneff and Mike Gray both mentioned the shell-collecting
possibilities after beach renourishment. Very interesting to hear what
happens in the offshore pits, Mike. Anyone else have more information on
that? It's hard to come by!

OK, shell collecting. I've never managed to get to a beach right after the
sand is pumped onto it, but I have visited Gulf Shores (Alabama) repeatedly
after renourishment. On the first visit, there were a lot of sharp, broken
shells, and they were oriented at all angles. There were complaints about
tender young feet being cut by shells, so we decided to look into that as
part of the beach renourishment project (that's called using a hammer
because you have a hammer in your toolkit). I identified the main offenders
as:
1. Bivalves with strongly ribbed shells that break along the ribs, e.g.,
Argopecten and Dinocardium, yielding 4-sided fragments.
2. Bivalves with robust, convex shells, e.g., Crassostrea (exhumed from
Pleistocene deposits offshore).
3. Bivalves with robust, flat shells, e.g., Dosinia, yielding triangular
fragments.
4. Gastropods with robust shells, e.g., Oliva.
As you can see, the fragile shells aren't really a problem despite the fact
that they splinter. Dosinia was one of the worst, because it yielded the
sharpest corners. But within a year, the problem had largely solved itself.
Most of the sharp edges were a bit rounded by then, and the waves had
reoriented the relatively flat bivalve fragments to horizontal instead of at
all angles. The snails, not being flat, continued to act like caltrops. But
all of this was pre-Ivan and a new round of renourishment is planned.

If you live on a beach that has never been renourished but where plans to do
so are in the air, why not make it your project to see what shells are there
already? I found that every kilometer of Alabama shoreline has a different
fauna, despite the fact that long stretches of it look much alike.
Apparently this is because the mollusks live offshore and offshore
conditions are not as homogeneous as beach conditions are. Some stretches of
beach consistently yield fossil oysters and bay clams; pen shells; bivalves
that bore in peat or clay; and other forms that are not otherwise common.
Well, you could knock me over with a feather.

So if you list the species of each stretch of beach separately, then you get
some idea of what's going on offshore. But if you wait till after the beach
is renourished, you'll never again see what would have been there naturally.
The clock's ticking.

Cheers,
Andy

Andrew K. Rindsberg
Geological Survey of Alabama

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