Summer is a great time to enjoy local shellfish. They are a valuable resource that exists right in the intertidal and are harvested by hand by local diggers. Both soft shell and hard shell clams live deep in the mud, their tell-tale siphon holes giving away their location to those who want to dig them up. Once they come out of the mud, many of these will get consumed fried, as steamers, or in a chowder. But, when you are done with the shells, what do you do with them?
The answer is, as often the case, not a simple one. It might seem logical to toss the shells back into the ocean. And, in some ways, that is a good solution. Ocean acidification is an increasingly familiar term for most people. Increasing Carbon Dioxide levels in the atmosphere have led to higher levels of acidity in the oceans and that isn’t so great for shellfish. Acidity erodes shells and makes them weaker and more vulnerable to predators as well as to infection. It also means there is less available Calcium in the water for shelled animals to use in growing and maintaining their shells. Putting the “used” shells back in the water helps to add back Calcium to the water and also to buffer the acidity level.
But, as I said above, it isn’t as simple as that. Shellfish can carry a variety of bacteria and other pathogens. And, those are often unique to a particular area. That means that, if you eat shellfish from one area and then put the shells back in a different area, you might unintentionally introduce tiny critters that can be harmful. Also, there are all kinds of bacteria that humans harbor so that, when we eat them, we might leave some of those behind in the shells that we discard.
So, what is the best solution? You might think that, if you put them in the trash, they would break down since they are composed of naturally biodegradable materials. But, this isn’t so straightforward either. Often, items that are biodegradable don’t break down so easily when combined with a variety of other types of trash. They don’t get the oxygen and air circulation they need to decompose easily.
Putting them in your compost pile or bin is a better way to give the shells the conditions they need to break down. If you break them up a bit as well, that gives them a head start. It also enriches the nutrients in the compost if you end up using it in your garden. There are several local composting programs that will even pick up bins from residences if you don’t have your own system at home.
Even better than that is to find a shell recycling program. Maine started a small pilot program through the Maine Coastal Program and the Casco Bay Estuary Partnership in 2019. The Ocean to Plate to Ocean program included the collection of oyster shells from restaurants in an effort to reduce ocean acidification. The program faced the same problem that I mentioned above – restaurants offer shellfish, including oysters, from a variety of locations and growers. That means they have to be properly cleaned before they can be returned to the water. The recycling company, EcoMaine, helped out with this part of things. Essentially, the shells have to be dried out for a period of time so that they are naturally disinfected. Then, it is safe to put them back into the water.
Ideally, there would be recycling programs like this in multiple towns along the coast in order to make it easy for people to recycle shells. But, as there are not currently, another option is to disinfect the shells yourself. This is pretty easy if you’ve got some space to spread them out. You can start a kind of “shell garden” where you put the shells after you’ve eaten them and leave them there until you’re ready to scoop them up and return them to the sea. Or, you can leave them there to enrich the soil. They dry out and disinfect easily with plenty of sunlight.
So, enjoy plenty of shellfish this season and find the best solution available to you to help return the Calcium they contain to the ocean in a safe and healthy way.
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