This is broadcast spawning, when all the oysters in an area release their sperm and eggs into the water column at once. When the time is right, one oyster will release its sperm/eggs into the water column, followed by all the other oysters in the area. The mating process kicks off in the summer once the water has reached a certain temperature. This takes place in spring and the gonad takes roughly two months to form. Environmental cues such as temperature, amount of food, and salinity determine if it's time for the oyster to develop sex organs (gonads). As time goes on, oysters are able to change to females, and even then change back into males, depending on circumstances. The Eastern oyster is protandric, meaning that they are all born male. Oysters begin their life the same way most organisms do, with the fertilization of an egg by a sperm. A single oyster can clean up to 5 L of water per hour, removing organic and inorganic toxins that could otherwise harm the ecosystem. While oysters do expel feces and pseudofaeces, they ultimately leave water cleaner. Every once in a while, the oyster claps its shell together and pushes out most of the water out of its body, along with any waste. The oyster covers them in mucus and stores the pseudofaeces with the actual feces. Pseudofaeces are things like sand or large pieces of food the oyster can’t digest. Besides to actual waste, items called pseudofaeces also collect there. As oysters digest food, waste collects in a cavity inside their shell. Oysters are filter feeders, and take in all different types of particles from the water column.
A single oyster can filter as much as 50 gallons of water in a single day, consuming the excess nutrients as food. Oysters remove the excessive organic particles before they have a chance to cause an algal bloom. This kills fish, crustaceans, and other marine life, disrupting the entire ecosystem. The water can become low in or devoid of oxygen (called hypoxic). When the bloom of algae dies off, its decay consumes oxygen. This is sometimes called an “algal bloom”. The high level of nutrients causes a spike in the amount of algae.
Too many nutrients can trigger a process called “Eutrophication”. Runoff from Human activities like farms, residential lawn care, and inadequate septic systems can introduce too many nutrients into the water.
But too much of these nutrients can be dangerous. Coastal ecosystems rely on nitrogen and phosphorus to support all marine life. Oysters serve an important purpose in removing excess organic matter from the coastal ecosystem. They prefer organic material with nutritional value like plankton. Oysters are selective in the material they take in. They use a small filter (called latero-frontal cilli) to grab onto potential food before releasing water back into their surroundings. They take in water from their surroundings and extract particulate matter from it. If you are interested in volunteering with the Great Bay Oyster Restoration program or other environmental stewardship programs, reach out to the New England Stewardship Network.Oysters are filter feeders.
We helped by volunteering a few hours on a sunny morning to count oyster spats that will be delivered to local homeowners that will monitor their growth. Now about 8 years underway there is a community effort to restore the oyster population. During the 1980s a deadly disease was introduced to the region that destroyed most of the oyster beds. The oysters were key to the health of the estuary. Great Bay had a long tradition of large populations of oysters that helped filter and clean the waters. Curious what an oyster spat is? Well, it's a baby oyster and UNH has teamed up the The Nature Conservancy and volunteer Oyster Conservationist to help repopulate this body of water with oysters. Although a majority of our projects are completed in the Lakes Region, this past July we were able to spend a morning at the UNH Jackson Estuarine Laboratory on the shores of the Great Bay in Durham to help count oyster spats.