Friday, July 20, 2012

Part 2: How do People Make Oysters?

UMD HornPoint Laboratories (HPL):  What an operation!  What a facility!  What a weird group of people!  (teasing…)  They started producing baby oysters in 1997.  Last year they produced 650 million spat-on-shell.  In a perfect world with a gentle mother nature, they hope to produce up to 1 billion.  Regardless, HPL is charged with jump-starting the oyster resurgence in Maryland’s Chesapeake.  Currently, our oyster population is at an all time low of 0.03% of historic levels.  The spat-on-shell that comes out of HPL is the seed oyster for our sanctuaries, harvest reserves and burgeoning aquaculture industry.   The Chester has been recipient for decades and most recently received seeded shell for a 2-acre oyster reef spear-headed by the Chesapeake Bay Foundation.

Alright, alright, but how does man make oysters and why is there such a variation in our Marylanders Grow Oyster  (MGO) cages!?  Well, people make oysters by first understanding the science of how oysters reproduce and then they must figure out how they eat.   By inducing female oysters to release eggs and male oysters to release sperm by methodically raising water temperatures, HPL can develop superior gametes from the fittest brood stock—hopefully enhancing the genetic fitness of our native Crassostrea virginica against disease pressure.  Once the gametes meet and form larvae, staff at HPL feed and monitor the microscopic swimmers through various stages of development. So here is how to make oysters:  you have to know how to make algae!  Oyster larvae eat algae, but not just any algae.  Their diet is a well-balanced buffet of different kinds of algae--highly regulated, highly supervised, and highly scientific!

Close monitoring of oyster larvae will reveal the formation of an “eye” or dark speck, that indicates the larvae are ready to set.   Ideally, we want the oysters to “set” on other oyster shells to form a reef, but they will set on anything.    So staff must drain massive tanks filled with millions of larvae before the larvae start attaching themselves to the walls and then……put them in the fridge!  Yup, millions and millions of oyster larvae can be stored right next to last night’s left-overs.    I don’t think there is a shucking knife small enough….

While the larvae are chillin’ out, the staff at HPL readies the setting tanks—located on a state-of-the-art pier that has recently been brought on line.   (Following the logic:  bring the larvae to the water, not the water to the larvae.  Much more cost effective!)  The setting tanks are where the larvae find their new home!   Each tank is filled with aged oyster shell that has been dried and cleaned by the Oyster RecoveryPartnership.  The vast majority of the shell comes from the Chesapeake’s shucking houses but a growing portion is coming from restaurants participating in the Shell Recycling Alliance. (Shameless plug: eat oysters at these restaurants; the shells will go back to the Bay with 10 more oysters attached!)

 Alright, so now we’ve got old oyster shell in water pumped straight from the Choptank River.  When we add eyed larvae looking to set, one precocious little oyster larvae will yell out, “follow me, I know where the prime real estate is!”  And that is when it happens.  Predictably unpredictably, oyster larvae will set in “clusters” on the shell, exhibiting what scientist call a “gregarious setting pattern.”  In other words, they like to grow next to other larvae.  The result is that the spat on shell coming out of the hatchery has a variation in density.  Some shell will have 15 spat attached to it and some shell will have 0 spat set to it.  

When our growers pick up their cages with spat-on-shell randomly distributed, each grower starts off with a different amount of spat to care for.  And then it happens.  Each member has different conditions for caring for our oysters!  It is one of the benefits of the MGO program; oysters come to our member’s home and become a real life aquarium at the end of their piers.  It is also one of the factors influencing the amount of spat on shell that survive the growing season and are planted on a sanctuary.  Each member will have to provide the right amount of care based on his or her water conditions.  That includes suspending the cages at the right depth to avoid lethal blow-out tides in the winter and dunking them periodically to avoid suspended sediments from settling on them to the point of suffocation.  And on top of all of that, we throw in the capriciousness of mother nature!  This past year, we experienced heavy spring rains that came down the mighty Susquehanna and essentially dropped the salinity to 0 at the Bay Bridge for a month or more.  Incredible.  Our spat-on-shell are equally susceptible to the harmful effects of low salinity, but there is little that we can do about that.   Some members that were exposed to the “freshet” coming down the bay experienced very high mortality.  Other growers in Langford Bay didn’t experience much of a difference from last year’s conditions--although there is some discussion that our oysters are a little smaller this year.

The best way to care for our oysters coming out of the hatchery is to follow the recommendations on the MGO website: hang the cages thoughtfully so they are not in the mud, but still underwater during low tides; then dunk them periodically to remove suspended silt--this can be as little as once a month depending on where you are and what time of year its.  But to get the full benefit of the program, don’t be shy about pulling up a cage with a friend or family member to see how the oysters are growing and what critters they have attracted into their mini ecosystem!

Mike Hardesty is Assistant Director of the Chesapeake Semester at Washington College and the MGO-Chester River Coordinator.

1 comment:

  1. Mike,
    What is the major challenge facing oyster survival? Introducing 650 million oysters sounds like quite a lot to me! So where do they all go? And is there any way that we could increase the survival rate?