Sunday, November 18, 2012

Counting Oysters in the San Francisco Bay


The Watershed Project offices
Yesterday we visited the Watershed Project in Richmond to help them with their study of oysters in the San Francisco Bay.  

The oysters are making a comeback after a problem that started back in the mid-1800s.  Apparently, during the gold rush, the miners used a method called hydraulic mining.  They pointed a high pressure hose at the hillside and sprayed away all the soil to just reveal the gravel and rocks beneath it.  This left them with a much easier task of separating the valuable rocks from the others.  Widespread use of this technique caused a huge amount of mud and silt to be washed down from the Sierra Mountains into the San Francisco Bay.  This was very bad news for the oysters because they require a hard surface to cling to.  As all the rocks became covered in silt, the oysters died off.

Oysters are filter feeders that can each process up to 20 gallons of water per oyster per day.  In that process, they remove nitrogen-containing compounds and plankton from the water.  This tends to help overall water quality and has an impact all the way up the food chain, so they are vital to the ecosystem.

Bricks from around the bay waiting to be counted
The Watershed Project is hoping to create new habitats to promote oyster colonies to help the overall ecosystem of the San Francisco Bay.  As part of this work, they are studying where oysters are likely grow by placing bricks in the water at various candidate sites around the bay on specially designed stands.  The Oysters like the hard surfaces these bricks provide.  They place the bricks in August and in November (now) they re-collect them to see what has grown.  It was our job (and other volunteers) to help with counting the number of oysters that were on the rocks.
A muddy brick ready to be counted
The bricks had been retrieved and carefully organized by other volunteers so that we could tell exactly which brick came from which location, how it was oriented and its depth in the water.  We then proceeded to count and record each oyster on the front, back, top, bottom and sides separately.  With only three months of growth, many of these oysters were very small (as small as 1 mm), but it was our job to count every one on each brick.  We had to differentiate between oysters, barnacles, limpets and other clingy critters.  Differentiating between these different aquatic bivalve, arthropod and gastropod mollusks was a bit daunting at first, but we quickly got the hang of it.

It was messy detailed work, but somehow very satisfying
Bix and Widdakay hard at work

Bix starts in on a brick
Widdakay measures an oyster


The bricks were muddy and eve a little bit smelly, but that didn't deter us.
We recorded the size of each oyster and the total number of oysters on each face of the brick.
Once the Watershed Project has identified the best sites, they plan to build artificial reefs that can grow oyster communities.  We were also fortunate during our visit to witness the donation of $40,000 to the Watershed Project by PG&E to help them continue this work.

Oh boy!  A novelty sized check!  woohoo! 
Overall, it was a fun and productive morning, and we felt good about helping out an important cause.

For more information, see the Watershed Project.