Occasionally
in a few places on the sandy beach along the Dutch
coast, one finds strings of shell debris together
with young mussels, about 20 - 30 cm long and
about 5 cm in diameter, strong and flexible glued
together by elastic threads, see the picture.
One may ask how these strings of broken shell
fragments and small mussels have originated and
what keeps it together. I will shortly explain
this phenomenon in this contribution to the magazine.
On
parts of the Dutch coast, where the dunes are
less developed or absent, break-waters are constructed
at regular intervals to prevent coastal damage
by heavy wave action. Only during low tide are
they exposed to the surface for some hours, otherwise
they are submerged and invisible from the beach.
These break-waters are made of basalt blocks which
provide a substrate for countless mussels, attached
to the rock surface by byssus threads. Most of
the time young mussels cover the rock surface
completely. In the crevices between the blocks
shell fragments accumulate and are mixed with
the young mussels as a result of wave action.
In these crevices, shell debris becomes attached
to the mussels by byssus threads produced by the
mussels. The mixture gradually increases in seize
and finally sticks out the crevice. In this stage
it can break away from the crevice by heavy wave
action and is then washed ahore.
Byssus
threads constitute a remarkable bioglue. It is
a filament produced by some species of mollusks
to attach themselves to the substrate. When the
foot of the mussel encounters a small crevise,
it creates a vacuum by forcing out the air. The
byssus, which is made of different proteins, is
spewed into this chamber in liquid form and bubbles
into a foam. By curling its foot into a tube and
pumping the foam, sticky threads are formed about
the seize of a human hair. With the help of another
protein, that is used to varnish the thread, it
turns into an adhesive. The mussel is able to
absorb byssus, enabling himself to move over the
substrate. Research has unveiled the chemical
process of producing byssus and it is expected
that in the future this bioglue may be used to
glue bone fractures and other internal injuries.
