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Farmed Scallops vs Wild?


Essie Martin of Hurricane island's Research team recently visited the Isotope Ratio Mass Spectrometer at Bates College and sends this report:


"Like everyone who works on Hurricane Island, I spend a decent amount of time interacting with students. As researchers we are often called upon to answer questions about our aquaculture farm, spat bags, and general scallop facts. One question I get a lot (and a question I ask myself) is if there is a difference between our farmed scallops and the adjacent wild populations. Genetically the scallops are homogenous– we seed our farm with wild spat. But the two grow in different conditions; different depth, different proximity to other scallops, different temperature, etc.… So is there a chemical difference brought on by their divergent growing habitats? What might that indicate? Thanks to a grant from the Davis Conservation Foundation I am pursuing answers to these questions using stable isotopes this season.


Perhaps you’ve heard of radioactive isotopes — the kind used to date dinosaur bones; but most people haven’t heard of stable isotopes. When I first signed up for a stable isotopes class in college, my dad made fun of me, saying I’d just put two big words together to sound impressive. So what are stable isotopes for all you curious minds in the audience? (Yes, even you, Dad.) Isotopes are any atom of an element with an atypical number of neutrons. For example, a normal carbon atom has 12 neutrons, and a carbon isotope has more or less neutrons than the normal 12. Some forms of isotopes are unstable– they will eventually return (“decay”) to the “normal” number of neutrons for their element. For our carbon example, an unstable form of carbon is carbon 14 (a carbon atom with 14 neutrons). Overtime those carbon 14 atoms will decay to carbon 12, and the ratio of carbon 14 to carbon 12 allows us to date artifacts. Other forms of isotopes are stable and can exist indefinitely in their state. Carbon 13 is a stable isotope form of carbon.


Stable isotopes are used in geochemistry to detect source materials (such as food and water), recreate paleo climates, and even in forensics. The way we measure stable isotopes is by taking the ratio of normal atoms of an element to the corresponding target isotope. Depending on the situation we measure different elements. For the purposes of identifying differences between farmed and wild scallops, we chose to use organic isotopes: Nitrogen 15 and Carbon 13. Organic stable isotope analysis can help us differentiate energy fluxes from local primary production, nutrient gradients at depth, and general food sources. This information may help to inform shellfish closures, best farming practices, and possible impacts of ocean acidification and warming on scallop physiology. Nitrogen isotopes may also indicate possible anthropogenic influence close to scallop growth due to signature isotopic composition of human waste and fertilizer. We plan to sample scallops for isotope analysis in the middle of each month from June-October (with an additional sample at the end of August during scallop spawning) from aquaculture nets, aquaculture cages, and adjacent wild beds. We will sample 5 female and 5 male scallops from each source. Thanks to our continued collaboration with Bates College, we will analyze scallop samples on the Bates campus using their Isotope Ratio Mass Spectrometer (IRMS). Stay tuned for results soon! "









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