Don Meritt, director of the Horn Point Hatchery, explains how recycled oyster shells are left outside the Cambridge lab for about a year, in order to allow organic matter to decompose naturally before the shells are reused. (Photo: Sarah Polus)
CAMBRIDGE, Md.—One Maryland lab is using science to artificially create, feed and grow oyster larvae—no bigger than a grain of sand—in order to help restore the Chesapeake Bay.
The Horn Point Hatchery, one of the largest oyster hatcheries on the East Coast, wrapped up its most successful season yet, producing a record number of oyster larvae that have successfully set into a shell.
Don Meritt has been working at the Eastern Shore lab since it opened in 1973. Since then, he has managed to rise through the ranks in the oyster program, transitioning from his start as an intern into his current position as director. The scientist now oversees the program, and its oyster re-population strategies, with ease and excitement.
Meritt said overharvesting, overpopulation of the watershed region, habitat destruction, disease, nutrient excess from runoff and sedimentation issues are the major problems affecting oysters’ ability to repopulate naturally.
Although the lab conducts environmental research, its main focus is to “bring back healthy oyster populations to the bay through outreach and production,” Meritt said.
The Horn Point Hatchery is run by the University of Maryland Center for the Environment. The lab works with the Department of Natural Resources and the Chesapeake Bay Foundation, among others. The Oyster Recovery Partnership provides and cleans the shells the hatchery uses.
The hatchery operates year round, but only grows new oyster spat during the summer months. Once the spawning process begins, it operates 24/7, until the water becomes economically unfeasible to heat. The lab finished growing its last batch of oysters in September.
According to Meritt, oysters begin to reproduce at approximately 3 years old, and draw on hints from their environment to begin the process. The hatchery carefully simulates these environmental factors, including proper water temperature and salinity levels, in order to “trick” the oysters into producing sperm or eggs at any time during the lab’s growing season.
In the winter, oysters enter a dormancy-like period where they don’t feed, grow, filter or reproduce. Once the water warms, typically after early June in Maryland, oysters begin spawning—releasing eggs and sperm, over a period that lasts about 20 to 25 weeks.
Oysters are broadcast spawners, meaning that they expel eggs into the water and fertilization occurs outside the animal’s body.
Only one oyster needs to spawn in order to create a successful batch, as other male oysters will release their sperm once they detect foreign sperm in the water, Meritt said. Within 12 to 24 hours, larvae develop shells and the ability to swim around rivers, a state which they remain in for two to four weeks. During this stage, larvae are carried by river currents, making them extremely susceptible to water quality changes.
Once the oysters are a couple of weeks old, they get too big and swimming becomes difficult, so they grow an appendage similar to a foot and use it to look for a suitable shell. This is a crucial period, because they only have a few days to find a habitat before they die.
“Oysters get one shot to determine where they’re going to live for the rest of their lives,” Meritt said. Availability of material suitable to settle down on, good water quality and healthy larvae at the right stage are all factors that have to align for success.
Once they set, the foot uses an adhesive to attach, which allows the larvae to avoid being eaten and transform into an adult oyster.
“At this stage, they’re no bigger than a grain of sand,” Meritt said, explaining the complex operation. In the hatchery, the process is artificially conducted by placing larvae in tanks, where they can settle on clean shells. Once the larvae have successfully attached to shells and transformed into oysters, the Oyster Recovery Partnership plants them in the bay, Meritt said.
The hatchery goes through about 65,000 bushels of shell per year. Most shells come from shucking houses, but about 15,000 bushels come from the oyster shell recovery program, which collects shells from restaurants and consumers.
Before the shells can be utilized, they must be rid of all organic matter. The most cost-efficient method of doing this is leaving the shells outside in piles to decompose naturally- a process that takes a year. Once they’re ready, a shell washer removes any remaining particles.
This intensive process may create a perfect growth environment for oysters, but that means the conditions are ideal for other species to develop as well. The lab uses filter tanks to remove any species that may compete with the oyster’s growth, but this process also removes the oysters’ food source, so food must be artificially produced.
Oysters feed on algae, but on different types and densities throughout their growth stages. The lab produces four different mixtures of algae. Computer monitoring systems automatically feed the correct percentage of algae concoction about six times a day into their tanks.
Despite the complexity of the program and the time and money demands it requires, Meritt believes the lab’s efforts are paying off: “Last year we a produced a record,” of larvae that had successfully attached to shells - 1.25 billion, he said.