We’re trying to help Mother Nature back. We’re trying to plant these in places where they can spawn and provide those benefits, and help her get broodstock back, so when conditions are right, she can have this massive spawn.
The Broddus and Margaret Ann Jones Oyster Culture Facility at the University of Maryland Center for Environmental Science's Horn Point Laboratory is one of the largest oyster culture facilities on the East Coast. It produces a variety of oyster larvae for use in oyster research, oyster restoration, and educational projects.
In 1972, Tropical Storm Agnes tore through the region and devastated already vulnerable populations of oysters. Two years later, our researchers began what would become an ongoing effort to restore oysters in Chesapeake Bay.
The researchers quickly outgrew the original facility, eventually moving into the Aquaculture and Restoration Ecology Laboratory in 2003. This newer space is not only larger, but also provides quarantine and controlled environmental facilities.
“Every year since then, we’ve been getting bigger and better,” said Stephanie Alexander, oyster culture facility manager. “We have really nice technology that allows us to do what we’ve never done before. To give you some scale, in 1997 we did about 10 million spat on shell. They were all by hand shell bags. Then we started to get a little more advanced and started to use stainless steel containers, having machinery to do all of the lifting. As of 2016, our best year, we did 1.78 billion spat on shell.”
Oyster Recovery Partnership
In 1993, Donald “Mutt” Meritt joined an oyster roundtable called together to address concerns about the low population and devise possible solutions. A year later, the Oyster Recovery Partnership was established, and with it came an action plan for how the Horn Point oyster culture facility and its partners could begin to rebuild the populations lost over time. Learn more about the partnership and its successes.
“What I’m really proud of is the scientific background that UMCES has, and the facilities we have that wouldn’t be here if it wasn’t for the crisis in oysters. I think we’ve done a really good job of applying new, state-of-the-art techniques for oyster restoration,” Meritt said.
How to raise an oyster
The culture facility encompasses a series of systems, each with its own special purpose to allow staff to control aspects of the oyster’s life cycle and to produce large numbers of oysters for use in the partnership’s programs.
“You can’t have a hatchery for anything unless you can hatch things, and oysters or chickens—whatever you’re trying to hatch—you have to be able to get the eggs in the right stage,” Meritt explained.
An oyster’s life starts the same in the culture facility as in the wild.
Once fertilized, an egg will drift with the water until it develops into a larva. These larvae will live in the water column for the next two to four weeks, swimming in the currents to find food while they mature.
At about the two-week mark, the larvae enter the pediveliger stage. Using an appendage they grow called a foot, the larvae will begin to move around in search of a hard surface (like an oyster shell) to attach themselves using a glue that they secrete. At this point, the larvae undergo complete metamorphosis of internal anatomy and become what is called a spat.
In the oyster culture facility, larvae are kept in 12- by 12-foot tanks in their initial weeks.
“The water in the larval tanks is kept at the proper temperature that’s finely filtered down to one micron because we’re trying to create the perfect environment to grow larval oysters,” Meritt said.
The staff drains its tanks twice a week to keep them clean and regularly filters the water to keep copepods, larval worms, and other organisms that the hatchery doesn’t want to grow from making a home in the tanks. Larvae are retained on a screen as the water pours through. Once empty, staff will scrub the tank, refill it, and return the larvae.
The larvae are fed a specially made batch of algae while they grow in the tanks.
“We grow generally four species of algae that we use to feed the larval oysters, and that’s basically all we feed them. Each algal species has its own set of nutrients. Like everything we eat—potatoes have different nutrients than broccoli and steak—we need to feed them a balanced diet or else they don’t do very well.”
Algae are grown in large glass flasks, and eventually used to inoculate larger mass algae tanks, which grow the vast quantities of algae needed to feed the larvae. The hatchery has an automatic feeding system that staff can monitor using a computer.
This homegrown food is a vital part of the larvae’s—and the culture facility’s—success rate. Newer to the mix in the past 5 to 10 years are diatoms, which are high in lipids and help the larvae through the stressful metamorphosis stage. The more larvae that make it through this stage, the better potential for more oysters later on.
“We would get, on average, about 1 percent, maybe on a good batch 2 percent, of setting efficiency. We’re now averaging over 30 percent, and much of that I attribute to the fact that not only are we giving them a better diet, we’re giving them all the diet that they need,” Meritt said. “In the old hatchery, we had very limited algal production capabilities. The larvae were basically starving or they were getting a very poor diet, and they responded appropriately.”
Larvae only live in the tanks for two to four weeks, and the culture facility staff regularly check on the larvae to make sure they’re removed from the tanks on time.
“If you put larvae that are ready to set back in the larval tank, they’re going to set on the only thing in there to set on—the larval tank—and the only way to get them off of that is to kill them and scrape them off,” Meritt said. “If you put larvae that need a couple of days of development into a setting tank, the conditions of the setting tank aren’t generally conducive and they die. So it’s really important that we put them out at just the right time and the right size.”
To see if they’re ready to set, staff pour the larvae through a set of decreasing sized sieves. The top layers will catch the larvae that are ready for the next stage. The fourth layer will signify the larvae that are close, but not quite ready, and they will go in an intermediate tank for another 24 hours. Any that make it through all four screens will be returned to the larval tanks. For the larvae that are ready, the next stage is the setting process.
The setting process
Near the oyster culture facility at Horn Point Laboratory is a yard filled with piles of oyster shell. Here the Oyster Recovery Partnership, with help from the Maryland Department of Natural Resources, amasses tons of shell that will eventually serve as new homes for the larvae Meritt and his team grow.
Before the shell is ready, however, it must be stored for a year to make sure organic matter rots off the shell. Then the shell is run through a washer and grater before it is divided into several tall but narrow stainless steel cages. The cages ease transport of large volumes of shell from the shell yard to large water tanks on the Horn Point pier on the Choptank River. The Oyster Recovery Partnership puts the cages in the tanks, and the hatchery fills the tanks with water. Then the larvae go in.
“We dump 2 to 4 to 5 million larvae in here, and we give them basically three days in order to go through that settlement and metamorphosis process,” Meritt said.
The water in the tank is static when the larvae go in, but once they’ve had enough time to attach themselves to a shell and go through metamorphosis, culture facility staff activate a pump with river water, which will bring in food for the spat.
The spat typically remain in the setting tanks for a few days before they are deployed to a grow-out site in the Chesapeake Bay. The culture facility signals to the partnership when a tank is ready, and they will load those tanks—usually about 10 per day—to a vessel that will ship them out to a predetermined spot that has been deemed suitable. One tank could yield between a half million and 1.5 million oysters.
The partnership will then clean the tank, reload it with cages of clean shell, and the process starts over with new larvae.