Oysters to the Rescue

New York City in the United States has an unusual way of cleaning up its polluted river: oysters.

Between July and December 2021, more than 11 million young oysters were put into the Hudson River. The Hudson River flows along one side of New York and into the Atlantic Ocean.

The oysters are part of a plan to create a healthier ecosystem in the river by increasing the oyster population.

(In this case, “ecosystem” means the species in an area and where they live, and how those things all work together.)

The waters around the mouth of the Hudson River used to be full of oysters. They were harvested for food and for their shells, which were in materials for roads and buildings. But people harvested too many oysters. The city also dumped sewage and harmful chemicals from factories into the water. By 1927, most of the oysters had died, along with many other marine animals.

Now, oysters may help to restore the waters and bring back more marine life.

How do oysters do it?

Oysters act as natural “water purifiers.” They are filter feeders. That means they take in water through their gills and filter out the food in it, such as plankton and algae, which they then eat. A single adult oyster can filter up to 189 litres of water in a day. As they feed, oysters also filter other, harmful things out of the water.

One of these is nitrogen, a chemical found in fertilizers and septic tanks. Sometimes nitrogen gets washed into rivers and oceans when it rains. Too much nitrogen in the water causes large amounts of algae to grow. The algae uses up the oxygen in the water, which can harm other marine life. Oysters and other shellfish filter nitrogen out of the water and use it to grow their shells.

Oysters filter other pollutants out of the water, too. These pass through the oysters and become solid waste which settles on the river bottom where it no long affects the water.

Oysters also build reefs, which are important to the whole ecosystem. Oysters attach themselves to hard surfaces underwater, like rocks or piers. Then more oysters attach themselves on top of those, and more on top of those. As the oysters grow, their shells fuse together to form a reef.

When the new oysters are placed in the Hudson River, they are attached to metal cages and mesh wraps which are submerged in the water. These become the foundations for new reefs, which will get larger as more oysters build on top of them.

Oyster reefs provide homes for plants and animals, which creates more biodiversity for the ecosystem. Reefs also help to protect the shoreline. Large reefs soften the impact of waves coming in from the ocean, and help to reduce flooding and prevent erosion of the coast.

It will take decades before the new reefs being created in the Hudson River grow as big as the reefs that were destroyed long ago, but there are already signs that the ecosystem is getting healthier.

Many marine animals have returned to the area, including crabs, seahorses, various fish, and even wild oysters.

THINK & DISCUSS

Using oysters to clean up pollution is a really creative solution. If you were given the task of cleaning up a river, what are some creative ways you might do that? (Think of as many creative ideas as you can–don’t worry if they’re too “out there” or might not work. Many great solutions were sprung from innovative ideas that seemed laughable at first.)

When the oysters in the waters off New York died, many other marine animals were affected because oysters are a “keystone species.” A keystone species is one that affects the way a whole ecosystem functions and influences which other plants and animals live there. Without these keystone species, some ecosystems would collapse. Can you think of any other keystone species? https://www.environmentbuddy.com/environment/10-examples-of-keystone-species/

Why (and how) do oysters filter water?

Look up these eco-related words from the article and write down their definitions (or define them in your own words): reef, filter, ecosystem, biodiversity, marine, nitrogen, plankton, algae, gills, pollutant, erosion. How many of them did you already know?

DIG DEEPER

Kid-friendly oyster facts: https://myfavouritepastime.com/2018/02/14/what-is-an-oyster/

Videos of oysters filtering water: