Oyster Farming: An inside look at the birth of your favorite shellfish.
Oyster Babies at 3 weeks old. Similar in size to a grain of sand.
Not everyone loves slurping down a sea creature that closely resembles a loogie in texture. For those that do, the allure of a raw oyster bar is hard to beat. Briny, buttery, and sometimes sweet, oysters are the closest thing you can get to tasting the ocean, without actually drinking seawater. But how these shell-clad filter-feeders end up on the beds of crushed ice in restaurants is unknown to most ostreaphiles (read: oyster lovers). It all starts back at the hatchery.
Hannah Pearson (Left), Hatchery manager and Ursula Balmer (right), Farm Manager, walking through rows of farmed oysters at Island Creek Oysters.
As ecosystem engineers, oysters create ecosystems for other species. Their extensive reefs act as storm buffers, create habitat for young fish, and purify 50 gallons of water a day (per oyster, that is). This is why oysters have long been used in restoration projects. Wild oyster reefs have been largely wiped out due to overharvesting, disease and pollution, and most of the oysters we eat today come from farms.
I asked Hannah Pearson, hatchery manager of Island Creek Oysters in Duxbury, Massachusetts what all goes into the rearing of these wondrous little bivalves. It turns out- quite a bit! Every farm is a little different, but for Island Creek Oysters, it begins with a beauty contest.
The most attractive oysters are selected from the bunch to use as breeders (or broodstock). Spreading their quality genes to the next generation is the goal. “We call them handsome devils,” says Pearson, “they are cherry-picked all year long from our farm.” What makes for a handsome devil? A nice deep cup, meaty body, and frilly edges. Island Creek sells oysters live for the half-shell market, so appearances are everything. “From my perspective, I want a nice big gonad and lots of eggs or sperm coming from that,” says Pearson. That’s because come February, these oysters will have one job: spawning.
Hatchery Manager Hannah Pearson holds hundreds of baby oysters in her hands. Not quite big enough to survive on the muddy bottom of the farm, they are kept in a nursery until they are a bit hardier.
Holding a light to the pyrex container shows the tiny white eggs released by one oyster in the hatchery. The eggs will be collected and fertilized to produce swimming larvae.
Oysters naturally spawn in the warm summer months, because the water temperature allows the babies to survive. Summer can be simulated in a hatchery by slowly turning up the heat over the course of weeks. The warming water and a steady diet of microalgae make oysters fill up with eggs and sperm; a process called ‘ripening’. Pearson keeps tabs on this ripening process leading up to the main event. She shucks a few oysters, scraping some of the gonad onto a microscope slide. The sperm are too tiny to see, so she looks for the slightest movement in the sample instead. “You don’t want to make them spawn before they’re ready,” says Pearson.
The farm cultivates huge volumes of micro-algae to feed the oysters in the hatchery. In order to get the oysters ready to spawn, the hatchery team will feed them every four hours.
When the broodstock are ripened up they are placed in groups of 20 to 30 in a shallow black tank to spawn. The white eggs and sperm are more easily spotted against this contrasting backdrop. The biological magic happens when the first male oyster leads the charge; releasing a cloud of sperm into the 80-degree water that the females filter in. Once the first oyster starts spawning, the rest will follow suit. Within about two minutes all of the oysters will be doing it.
Females release hundreds of millions of eggs at a time- but that is nothing compared to the number of sperm spewed by the males. Without careful intervention, the sperm can overwhelm the eggs; multiple sperm will attach to each egg. This “polyspermy” will deform and kill them. The hatchery team stands at the ready to remove each oyster from the tank once it starts to spawn. Relocating oysters to their own pyrex dishes allows them to keep the eggs and sperm separated.
At this point the team can mix the eggs with just enough sperm in buckets. Cells divide in the fertilized eggs until microscopic swimming larvae form. In the wild, larvae would travel with the currents, but in the hatchery they are collected and placed in tanks. Two weeks later they develop a muscular foot. Like toddlers, they begin to crawl around on the bottom of the tanks searching for a suitable place to settle in for good. Raising baby oysters requires tender love and care...and impeccable timing. The job even has a flashy name: larviculture, and it’s incredibly important for farms. Keeping these baby oysters alive and growing is priority number one. Come summertime, the farm will sprinkle 15 million quarter-sized oysters into the Duxbury Bay. This will be their final home for the next two years before being harvested, shucked, and slurped by peckish oyster lovers everywhere.
This article was originally posted on Forbes and is written and provided by Ariella Simke