Date:  03/27/1998  09:16 am  (Friday)
      From:  Roland Anderson
        To:  conch-L
   Subject:  Shell dissolution
 
Hi Folks,
Paul Monfils asked several questions about my
octopus/bottles/shell project which I'll try to answer here.
A small octopus species, Octopus rubescens, which only gets
to about 200 g, lives in beer bottles here in Puget Sound
(Wash. State, USA). They appear to be foraging on small
mollusks such as Olivella baetica, Alia spp, Odostomia spp,
Eulima spp, et al. on a sand bottom. They take the shells into
their beer bottle dens to eat, and discard the shells in the
bottles. They don't appear to make a midden outside their
dens, as do other species of Octopus (we have the world's
largest species of octopus, Octopus dofleini, which is
sympatric, which leave big messes of crab and mollusk shells
outside their dens). We've found statistically more shells inside
the beer bottle dens of O. rubescens than in unoccupied
bottles. There's a hitch here, Paul, in that the octopuses are
selecting certain beer bottles to occupy, those that are brown,
and those that have a covering of barnacles or sea anemones,
hence the occupied bottles are a different population of bottles
than the unoccupied ones, and hence they have more shells in
them. Octopuses are known to be migratory and may not go
back to the same bottles after foraging expeditions. Hence,
these bottles may be "fast food stands", where the octopuses
eat during the day (they're nocturnal hunters), where they leave
their "Big Mac" wrappers and styrofoam cups = shells.
 
Many of the shells in both occupied and unoccupied bottles
show slight signs of dissolution. I didn't count them if they were
crumbling. These are small shells, less than 1 cm, so I don't
think it would take much to dissolve them, if the processes
were right for dissolution. I have an experiment in progress here
at the Seattle Aquarium where I've put a number of these shells
into a beer bottle in sea water and plan to leave them for at
least 6 months, and will then examine them for deterioration.
 
Many thanks to all who had comments, questions and
suggestions about this project and about shell dissolution. I
think we've all learned a little more about shells and the
processes affecting them.
 
Best regards to all,
 
Roland
Roland C. Anderson, Puget Sound Biologist
The Seattle Aquarium
1483 Alaskan Way
Seattle, WA 98101 USA
206-386-4346
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