Oyster flatulence and climate science

Baltic shellfish in the shallows
Baltic shellfish are responsible for a significant amount of methane & nitrous oxide emissions
Image: Shutterstock

New research reveals that shellfish farts produce nearly 10 percent of the global-warming gases released by the Baltic Sea

Plans to expand aquatic farming could have a serious knock-on effect on climate change, climate experts have warned.

A study published in Scientific Reports shows that clams, mussels and oysters produce much more methane and nitrous oxide gases in the Baltic Sea than thought, up to ten percent of the total.

Oyster and blue mussel on the seabed
Oyster and blue mussel on the seabed
Image: CWSS/Bostelmann

Researchers have warned that shellfish “May play an important but overlooked role in regulating greenhouse gas production”.

Methane and nitrous oxide gases have a far greater warming potential than carbon dioxide. Shellfish in these ecosystems process the nutrients and release the gases as part of their regular biological processes.

Our results indicate that macrofauna increases benthic methane efflux by a factor of up to eight, potentially accounting for an estimated 9.5% of total emissions from the Baltic Sea.

Bonaglia, S., Brüchert, V., Callac, N. et al. Methane fluxes from coastal sediments are enhanced by macrofauna. Sci Rep 7, 13145 (2017). https://doi.org/10.1038/s41598-017-13263-w

Shellfish flatulence is not the first bodily function to be blamed for having an impact on the climate, the burps and farts of ruminant animals like cows are also a closely-examined source.

Ocean Desk Top Ten (title graphic)

10 facts about oysters…

  1. They’re incredible water filters

Every day, one oyster filters 50 gallons of water. The oyster draws water in over its gills using cilia, or tiny hairs. Plankton and particles in the water are trapped in mucus in the gill, then transported to the oyster’s mouth. This helps to keeps the water clean for other marine life.

2. They create communities

Oysters form beds or reefs that provide important habitat for fish and other creatures, including sea anemones and barnacles, which in turn provide food for bigger fish.

A close-up image of a Gulf Coast oyster bed
A close-up image of a Gulf Coast oyster bed | Image: EPA

3. A young oyster’s fancy is turned in spring

Oysters spawn when water temperatures rise in spring. Females release millions of eggs and males even more sperm and some of these lucky gametes meet in the open water. Fertilised eggs develop into microscopic larvae, drifting on currents and tides for around three weeks. Then, if something else hasn’t eaten them, the larvae attach to a hard surface, most likely other oysters, and transform into a tiny oyster called a spat. In areas where reefs have declined, oyster larvae may never find a place to settle.

4. Calming the storm

Oyster reefs provide an effective natural barrier to storm waves and sea level rise. They absorb as much as 76 to 93 percent of wave energy, which reduces erosion, flooding, and property damage from coastal storms. Oyster reefs are preferable to man-made rip-rap or walls which don’t provide other benefits, such as habitat, and cost a lot to maintain.

5. Irritation leads to beauty

Closely related to the food oysters (family Ostreidae) are the pearl oysters (family Aviculidae). When any small irritant such as a grain of sand gets inside an oyster shell, the animal covers it with nacre, or mother-of-pearl, the substance that forms the inside lining of the shell. Over several years, as more layers are added, a pearl forms. The type, colour and shape of a pearl depend on pigment in the nacre and the shape of the original irritant. Today, most pearls are cultured, or created in farmed oysters. Cultured pearls look just like natural ones but are considered less valuable.

Oyster bed
Oyster bed | Image: NC Division of Marine Fisheries, USA

6. Oyster reefs are under threat worldwide
Oyster reefs are the single most imperilled marine habitat on Earth, with 85 to 90 percent of wild reefs lost. The main culprit is destructive fishing practices, including over-harvesting, according to a report from The Nature Conservancy, along with habitat loss and declining water quality.

7. Reef restoration works
Fortunately, oyster reef restoration efforts are very successful. Some 80 restoration projects are currently underway around the U.S. with as much as 212 percent increases in oyster growth and 850 percent increases in other marine life on the reef.

Marsh grass and oyster beds
Marsh grass and oyster beds
Image: Steve Hillebrand, U.S. Fish and Wildlife Service

8. We can repair things

A variety of techniques work for oyster reef restoration, from shooting oyster shell from high-pressure hoses to placing bags of shells in the water. Some projects have built lines of shell and rock to stabilise the shoreline along with planting sea grass behind the reef to provide additional habitat. In areas without existing structure for “spat set” (a good location for young oysters, a.k.a. spat), seed oysters from hatcheries are used to establish new reefs.

9. Oysters face new pressures

As the oceans absorb more carbon dioxide, it changes the chemistry of the water. The world’s oceans have become 30 percent more acidic since the start of the Industrial Revolution, and that can kill oyster larvae and make it harder for oysters to form shells.

10. Oil is lethal to oysters at all stages of life

Oyster production in the Gulf of Mexico declined each of the four years following the BP oil spill disaster. A report from the National Wildlife Federation, Five Years and Counting, states “…oyster eggs, sperm and larvae were exposed to oil and dispersants during the 2010 oil spill can be lethal to oyster gametes, embryos, larvae, juveniles and adults. They can also have sub-lethal effects, such as reduced reproductive success.”

Unable to move away from such contamination, sedentary oysters are particularly susceptible.

Ocean Desk Make Waves (title graphic)

What can I do to help oysters..?

Support Local Oyster Projects

Unlike most seafood, oysters are a sustainable food and farming them is even good for the environment. Oysters purify the water they’re growing in and both native and farmed oysters absorb nitrogen and CO2 from the atmosphere.

Oyster Punt on the river Fal, Cornwall
Oyster Punt on the river Fal, Cornwall UK
Photo: Terry Tempest

Some methods of obtaining oysters are better than others. Try to use local suppliers, they tend to use more sustainable methods and small-scale harvesting techniques.

The ecology and marine life found in the shallow warm waters are fantastic. We have hauled in many tiny creatures and 99.999999% survive and are immediately returned, but the majority tend to move out of the way when they see the cloud of silt and we only want the oysters that are grounded!

Fal Oyster Company

Stop Eating Wild Oysters

Environmentalists can feel secure in giving decent oyster farmers their business. The trouble with eating oysters comes from slurping down wild specimens, which have been over-harvested and are struggling to survive.

There are not that many places left where wild oysters are sustainably harvested

Mike Beck, lead marine scientist with The Nature Conservancy
Oyster farming
Oyster farming’s sustainability helps to explain the increase in demand the delicacy
Image: Michael O’Meara

Recycle Shells

A simple way to make an impact is to recycle the shells. The same way other food scraps can be composted, empty oyster shells can be used in restoration projects, as they provide a surface for young oysters to settle on and grow. After they’ve formed a hard reef, oysters provide shelter for other marine animals and protect shorelines against erosion. Many restoration projects accept donated shells.

Returning shells back to the sea
Returning shells back to the sea | Image: Joe Raedle/Getty Images

You can also talk to local oyster bars and restaurants and encourage them to recycle their shells. Restaurants go through a lot more shells than a single person, so their donations are very beneficial for restoration projects with a shortage of shells.


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