Almost fifty years ago, when Haraldur Sigurdsson first came to the University of Rhode Island from Iceland, he got interested in what makes some clam shells more purple than others.
"I was living in Jamestown in the middle of Narragansett Bay and you get familiar with the quahog right away. And then you start to get curious about, you know, what's the wampum, what's this color? And I asked people, you now, the biologists who were working with me, and they said, oh well, we don't really know. We think it's some sort of contamination or something. We really don't know. Nobody knew. Incredible."
Haraldur as you might be able to tell, is a curious person. He’s 86 now, and he’s spent his life asking questions: making discoveries about things as varied as volcanic history and lake overturns and the meteorite that decimated the dinosaurs. And he just couldn’t believe that his colleagues weren’t at all curious about this purple color and why it was forming. This was important, he thought — not just for cultural reasons, like Wampanoag jewelry making, but also because it might be able to tell us something about this incredible food resource. So he started doing some testing.
"I had instrumentation in my lab that is called the electron micro probe and so I used that to look at the quahog and to look at the purple and the white parts," explained Haraldur.
At first, nothing. When it came to inorganic compounds, the shells — purple and white — were basically identical just calcium carbonates. So Haraldur set the question aside for decades until 2020, when he got access to some new testing equipment.
"Finally, I got to a lab at the University of Rhode Island Kingston campus that had a Raman spectroscopy sensitive to organic materials. And so I ran that, and what do you know? The white didn't show anything, really. But the purple showed a very strong peak for an organic chemical compound which is called polyene, P-O-L-Y-E-N-E."
Polyene is an anti-fungal compound. It’s in all kinds of anti-fungal drugs and once he began learning about it, Haraldur started thinking that the quahogs must produce it for the same reason we use it — to repel the attacks of fungi and other microbes.
"You know, one of the best wampum I've seen is coming out of the inner harbor of Mystic, Connecticut. But that's kind of like an appendix, that's kinda closed off to circulation from the ocean. Stagnant."
In contrast, in areas of open ocean, Haraldur noticed, quahog shells seemed mostly white, with little to no purple.
"And so the quahogs that were producing most of the polyene and getting the purple color were living in areas that were anoxic, low-oxygen, and a lot of nitrogen," he said.
The right amount of nitrogen for shellfish in general and quahogs in particular is a hot topic in fisheries management. Since the introduction of wastewater treatment systems, nitrogen levels in some coastal embayments have dropped. Some people argue this is a good thing and that we need to lower nitrogen levels to avoid harmful algae blooms, which of course no one wants. But, you need some algae for shellfish to eat, so other people have argued that nitrogen levels are now too low to sustain healthy fisheries.
"And the quahog fishermen are screaming, please, turn it on again," said Haraldur.
Haraldur is retired and says he’s not going to pursue this research himself. But he thinks that mapping out where quahogs have more and less purple in their shells is potentially a powerful tool for better understanding the relationship our local quahogs have with the nutrients and microbes in our waters and what they need to thrive.
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Learn more about the Shellfish Hatchery on Martha's Vineyard studying some of the same questions about why some quahogs are more or less purple.
Here's a link to the original Local Food Report that prompted Haraldur to get in touch with his findings.
