Backyard Biology

Nature stories from my backyard and beyond

Nature Stories

The Oyster Bar

Wednesday, September 1, 2010


You are cordially invited to the Oyster Bar to spend a day with some friends.   Your host for the day will be Crassostrea virginica, the American Oyster.

Please note that the oyster does not assume his duties lightly.  In fact, she would prefer not to assume them at all.*  It is just that once the oyster moves into an area, the value of the property increases and other creatures can’t wait to take up residence.

Directions to the oyster bar are simple.  Just grab your snorkeling equipment and head for the brackish waters of the estuary where it can be found in the intertidal flats out to the shallow waters of the bay.

What?  You don’t want to get wet?  Well, you will just have to settle for a few paparazzi photos of the goings on.  These can be had by closely observing a few oyster shells thrown up on the beach.  You see, not only does the oyster increase the value of the property - the oyster very often is the property.  Many of the animals living on the Oyster Bar live attached to the oyster.  So by inspecting his shells, you can get a good look at her neighbors.

The Oyster Bar is a family neighborhood.  After a wandering youth, many of the oysters return to the Bar to settle down.  The American Oysters release their eggs and sperm into the ocean where the eggs will be fertilized.  The larval oysters - called veligers - are part of the plankton, spending time wandering the ocean’s currents.  When it comes time to settle down, they will cement themselves to any hard object they come in contact with - often another oyster at the Bar.  Look for young oysters - called spat - attached to larger shells.  If the spat don’t survive, then all that will remain is the smooth scar from its earlier attachment.

The oyster spat are only one type of wanderer that might finally settle down to build on the Oyster Bar.  Many others might also leave evidence of their residence on the Oyster Bar.

Occasionally you might find the towering palaces of the barnacles attached to the oyster shell.  But often all that remains is their home’s foundation.  Look for a circular scar with ridges radiating out from its center.

While the barnacles occupy the high-rise dwellings, the single story apartments belong to the lacy crust bryozoans.  Each bryozoan is a tiny creature living in a boxlike apartment close up against its neighbor.  The effect of a bryozoan’s development is that of a crusty piece of lace stuck on the oyster shell.

While the homes of the barnacles and bryozoans are nice tidy affairs, the tube worm dwellings are random haphazard structures.  Their tube-like homes are built in a contorted, winding fashion, often crossing over or spiraling under each other.

Not all residents of the Oyster Bar build on top of the oyster shell.  The boring sponge prefers to mine its home through the oyster shell itself.  It will dissolve tiny holes throughout the shell and may even tunnel through to the inside of the shell.  However, the oyster seems to have no problem adding new shell material, keeping this unwanted visitor from entering its home.  Look for tiny shotgun-like holes that don’t quite make it through the shell.

The oyster is not quite so successful keeping out other unwanted residents of the Oyster Bar.  The oyster mud worm is able to enter through the front door.  Slipping between the oyster’s shells, it will construct a mud tube in which to live.  Being rather particular with whom it shares its house, the oyster will wall off the mud worm’s home with a layer of shell.  Look for a tunnel that extends to the edge of the shell.  

While the mud worm is an unwanted but tolerated guest, no one can crash a party at the Oyster Bar like the oyster drill.  As it’s name suggests, this snail uses its rasplike tongue to drill a small round hole through the oyster’s shell, through which it will devour the occupant.  There goes the neighborhood!  

The upper shell of the dearly departed oyster will break loose from the Oyster Bar and eventually wash up on shore.  Now is our chance to grab this snapshot of life on the Oyster Bar.


*Oysters can switch their sex from male to female and back again throughout their live.