Ready for a riddle? They clean water protect coastlines and repopulate the ocean with fish. They also grow without feed or fertilizer, sequester carbon and their remains can be re-used. You can also find them on your plate. Can you guess what they are? If not, get ready for a story of some spectacular shellfish. This oyster and these mussels along with scallops and clams are bivalves – ocean creatures with two attached shells. Fossil records place their age at over 500 million years old, before the dinosaurs and they are found everywhere, from the Arctic to the Antarctic, to the equator. They start out tiny, floating through the water. Oysters and mussels attach themselves to an underwater surface to grow while clams bury themselves in sand. They have no head, no organs, and gills that filter water. They come in all different shapes and sizes, too. They used to be so plentiful that they were given out as free bar snacks but overfishing caused populations to decrease. “About 85% of shellfish reefs worldwide have been lost.” Heidi Alleway did her PhD on the history of oysters and mussels. “We've had this extreme loss of a highly productive habitat from so many places in the world, and people didn't even know that it had happened.” The more we learn about how valuable they are to ecosystems, the more devastating this loss becomes. That’s because they do some incredible stuff and all by hanging out in the water. Wherever they grow, they’re busy cleaning because the majority of bivalves are filter feeders. “They filter water and catch particles in that water. So feed on those particles.” Sergei Katsev researched how mussels are controlling the ecosystem of the Great Lakes in the United States. “If you can imagine a mussel sitting at the bottom of the lake, maybe in 200 meters depth, and you imagine that water column 200 meters above that mussel, that single mussel can cycle that column of water in a couple of hours.” They use whatever particles they need to grow, and excrete the rest in a form that bacteria on the bottom can break down. As you can see on the left, they filter chemicals necessary for plant and animal growth: phosphorous and nitrogen. These chemicals are present in agricultural runoff from fertilizers and can cause toxic algal blooms at high levels. Bivalves also filter more than just chemicals. Pilot projects are using them to clean lakes and oceans of microplastics — tiny plastic particles hard to see and collect. The bivalves absorb the small ones and larger particles are excreted in feces, which can then be taken out of the water. So, we can use these animals to clean up polluted water but in a closed environment they can alter the whole ecosystem. That’s what the researchers discovered in the Great Lakes. The mussels aren’t native to this area and have cleared the water of nutrients too well. “It was quite a realization to figure out that mussels that live at the bottom of the lake have this large effect on the biology of the entire lake.” In the open ocean, it's a different story. Here, mussels and oysters can form reefs able to support whole ecosystems. Oysters are particularly good at this. “Over time, these structures grow bigger and bigger and they are very complex.” Katie Mosher works for the Billion Oyster Project, which aims to restore one billion oysters to NY’s harbor by 2035. As the oyster reefs grow, ocean plants attach to them which attracts small fish and other animals. “They become a nursery and a feeding ground for all different kinds of organisms. So hundreds of other species, fish, crabs, little tiny benthic organisms, will make their home in an oyster reef.” These reefs also support other larger animals. A study on New Zealand mussel reefs found over ten times as many fish near them and seahorses have returned to the oyster reefs in New York harbor. Their benefits also extend beyond the structures themselves. “What those oyster reefs are doing is actually protecting the integrity of the broader ecosystem.” When a powerful wave comes in from the ocean and hits an oyster reef some of the energy is broken up and lost, meaning the waves that pass that reef aren’t as damaging. Near the shore, this protects fragile coastal ecosystems, like sea grasses, which function as nurseries for ocean animals and as carbon sinks. Less wave energy also means less coastal erosion. And these ecosystem benefits can also come from farms if they are sustainably managed. “Having mussels inside any ecosystem is very beneficial.” Bokamoso Lebepe works with mussel farmers in South Africa to make sure their operations are as sustainable as possible. “Those sustainable fishing practices are, for example, trying to ensure that we minimize our interactions and impacts with endangered, threatened and protected species.” Mussels are hung from ropes suspended in the water that animals could become trapped in. But with the ropes properly anchored It’s extremely rare that this happens. “We also try to ensure that the mussel farms themselves do not have a big impact on the benthic habitats that they operate over.” In a closed environment like this bay excrement from the mussels could cover the ocean floor so platforms are rotated to make sure they don’t overwhelm ecosystems. Bivalve farms require no feed and no antibiotics, as they get everything they need from the water. Rope-grown mussels have a carbon footprint of 0.25 kg per kilo. For comparison, beef is around 100 kg per kilo. Out of the water, bivalves go through a process called depuration — they're placed in clean water to remove pollutants dangerous to human health. Microplastics are harder to remove. But even if you don’t eat shellfish, you could be consuming one credit card of microplastic per week. And unlike other methods of food production, waste products from mussels and oysters can be re-used in a circular way. “The farmers that we're working with now, they're working with a third party operator who actually uses the leftover shells to make organic compost out of them.” As building material, the shells also sequester carbon. Bivalves pull it from the water, and use it to grow their shells. Crushed up, the shells can be added to concrete instead of limestone. But the best use for the shells is the simplest. Growing more bivalves! Old shells are often re-used for farming but can also go to restoration projects where they’re left in the water instead of eaten. These projects are springing up around the world, from Australia to NYC. This is where the oyster really shines. “Every year we're collecting oyster shell from New York Harbor restaurants. So we've collected almost two million pounds of shell already.” The shells are cleaned and placed in cages. “These oyster cages are put into shipping containers that we've converted into a way to set oyster larvae onto shell.” Add water from the harbor. Then some larvae and after a week, there are baby oysters. The cages are then moved into the harbor. As the oyster reef grows, it creates an ecosystem while also benefiting people on shore. “We can expect a tonne of fish per hectare of oyster reefs to be added to the marine environment through a restoration process." So while more bivalves generally mean cleaner waters, the positive impact of mussels and oysters can be doubled through circular uses for their shells. And of all of them, oysters are the superheroes. Filtering, sheltering, protecting, and restoring. And in my opinion, they’re the tastiest, too. That’s why we should be doing everything we can to put more of them in our waters. “What I love about doing these vidoes is that you always learn something new. Today, for example, I learned how to shuck an oyster. And in the US, where I’m from, we put our oysters in vodka. If you liked this video, don’t forget to subscribe, we’ve got new ones every Friday. Cheers! ”
