Where Do They Roam before They Grow Up to Be Scallops? A Graduate Student Peers into Shellfish Larvae's Mysterious Pathway to Adulthood

Article excerpt

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With a cool ocean breeze under a cloud less sky, children weave small sailboats through the channel Larger boats scurry out of Waquoit Bay to fish in Nantucket Sound or spend a day at Martha's Vineyard. People not on the water are hitting tennis balls or relaxing by the beach.

It's a typical summer day at the Menauhant Yacht Club in East Falmouth, Mass. A picture-postcard scene you could find at any yacht club on Cape Cod in July--except for a tangled hose attached to a pump and a littering of filters and bottles spread out on a floating dock. A young woman in pigtails leans over the dock to pull two large orange bags from the water. For the most part, people are too busy to inquire why she's there, but occasionally some do.

Meet the 'Bug Girl'

For the past three years, I've spent my summers sampling Waquoit Bay for larvae of clams, scallops, and oysters. I sample wherever and whenever I can. I've sampled from docks, boats, and kayaks; at boat yards, yacht clubs, and research stations. I've sampled weekly, daily, and even for 48 hours straight. All this sampling has earned me the nickname "Bug Girl" with some of the harbor masters in the bay.

Larvae and other plankton are like the bugs of the sea. Suspended in the water, floating in unseen hordes, larvae are transported by wind and tidal currents until they settle and grow into adults. But this critical stage in the life cycle of shellfish remains largely a mystery. Larvae are small, and their paths are hard to follow. The larvae of bivalved shellfish are nearly impossible to identify, even for an expert. But I hope to overcome these obstacles with my doctoral research in the MIT/WHOI Joint Program.

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Understanding bivalves' larval stages could reveal ways to help reverse the population declines of shellfish. In the town of Mashpee, on the eastern side of the bay, shellfish constable Richard York has a vested interest in my study. He grows millions of adult shellfish to place into the bay each year for a commercial and recreational fishery, but he can't tell if they produce larvae.

To find larvae, which are no bigger than fine grains of sand, I have to filter hundreds of liters of water and count them under a microscope. When people find me working, they often ask me about the water quality. Some want to know if there are fish around, or why there was a blue crab die-off this spring. I don't always know the answers to their questions; I've lived on Cape Cod for only three years. Many of the people I meet have come here their whole lives and know more about the bay than I ever will.

On this particular day at the club, a man and his son pull their boat alongside the dock as I'm rinsing orange mesh bags used to collect larvae. The red-white-and-blue theme of their clothing reminds me that a popular holiday is approaching, which is also reflected by an increase in boat traffic. The man asks me if he can borrow the hose to wash his boat. "May I ask what you are doing?" he says.

"I'm looking for shellfish larvae," I tell him; it's my default response to this common question. I wait to gauge a person's interest before adding more details. This time their interest seems to have been sparked, as the son, who looks to be around 10 or 12, climbs out of the boat to look in my bucket.

"Do you see any?" he asks.

I tell him they are small, and you need a microscope to see them. Under a microscope, larvae appear as transparent semicircles with tissue containing digestive organs and swimming appendages. Just like adult shellfish, the larvae have shells made of aragonite, a calcium-containing mineral. When viewed using a polarization filter, the crystals in the larval shell cause it to reflect bright color patterns. The patterns produced are different for each species and, with the help of a computer and image-recognition software, can be used to distinguish individual species. …

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