Bay Scallops
Island Science

Bay Scallops, Nantucket Gold

• by Dr. Sarah D. Oktay, Managing Director UMass Boston Nantucket Field Station •

Bay Scallops Nantucket is home to the last commercially viable “wild” bay scallop fishery in the U.S. (and essentially world-wide) and preserving this treasure is, in a way, tantamount to preserving Nantucket.  Other fisheries up and down the East Coast have been significantly dependent on augmenting their scallop populations with scallops grown in cages or otherwise introduced into the population.  Although the Town of Nantucket does provide spat scallop that have been grown out from larvae as a way to boost recruitment (number of baby scallops who decided to stick around and grow to adulthood), the population in the harbor is just barely able to procreate enough, barring any disasters, to replenish the stock.  A severe storm, or algae bloom or metabolic deaths or loss of the essential eelgrass habitat due to shading of the water column can put stress on our scallop population. The ebb and tide of the fishery fortunes that can be derived from our coastal waters is dependent on our awareness of how we can adversely affect shellfish populations and essential fish and shellfish habitats.

Let’s back up a bit for those who may not know a lot about our famous native.  A scallop (pronounced locally as scow- LUP) is a marine bivalve mollusk of the family Pectinidae. Scallops are found in all of the world’s oceans.  Many scallops are highly prized as a food source and the brightly colored, fan-shaped shells of some scallops, with their radiating fluted pattern, are valued by shell collectors. From the website, Online Etymology Dictionary, the word “scallop” is derived from the Old French word “escalope” meaning “shell” which couldn’t be more straightforward. Many paintings of Venus, the Roman goddess of love and fertility, included a scallop shell in the painting to identify her.  This is evident in Botticelli’s classically inspired The Birth of Venus (also known as Venus on the half-shell).  Scallops also metaphorically and allegorically pave the way for pilgrims on the Christian pilgrimage route El Camino de Santiago (the Way of St. James). I found the practical and symbolic role of the scallop for those pilgrims fascinating (more at

Bay scallops are comprised of three subspecies over their range. Our native scallop, the northern bay scallop, Argopecten irradians irradians, ranges from Cape Cod, MA to New Jersey where it intergrades between New Jersey and Maryland with the southern bay scallop, A.i. concentricus, which can be found from NJ/MD down the south Atlantic Coast, around Florida, and westward to the Mississippi Delta. The valves of A. i. concentricus are more convex and are thicker and harder than those of A. i. irradians. The third subspecies, the Gulf bay scallop, A. i. amplicostatus, hangs out in the Gulf of Mexico down to just south of the border of Mexico.

Unlike most bivalves, which are oblong or oval, the corrugated shell of the bay scallop is relatively circular. The bay scallop has a strong hinge muscle within the shell but does not have a foot for digging or a siphon for water intake. Along the edge, or mantle, of bay scallop shells are 30 to 40 bright blue eyes. Each eye has a lens, retina, cornea, and optic nerve, enabling it to see movements or shadows and to detect predators. Along the edge of the mantle are tentacles containing cells sensitive to chemicals in the water; these cells help the bay scallop react to its environment. Bay scallops swim by clapping the two sides of their shell together to force water away from the mantle cavity and scoot along pretty comically. When bay scallops are young, they attach themselves to objects such as eelgrass by means of a byssal thread. This helps them avoid bottom-feeding predators, such as conchs and sea stars. As bay scallops grow, they drop to the sediment surface in the vicinity of eelgrass beds and move on to tidal flats or shallow sandy areas to feed at high tide. Scallops are one of the few bivalves that don’t bury themselves; they have a clean side face down in the sand and a “dirty” side facing up that accumulates algae and small barnacles and growths.

Bay scallops (Argopecten irradians irradians (L.)), have a relatively short life span, generally between 18-30 months in the northeastern USA, and it is theorized that only a few scallops survive to participate in a second spawning event. In northern areas like Nantucket, bay scallops can spawn in both the late summer and early fall when the temperature in the water columns drops or rises through the range of 68-72 degrees.  It can be argued that the bay scallops process of having two spawning periods, one in late spring and one in early fall, is a type of “bet hedging” that allows a population to overcome hurricanes, red and rust tides and other natural or not so natural disasters. Annual recruitment of juveniles is highly variable, and thus the abundances and landings of market-sized bay scallops have been highly variable from year to year as we have documented on Nantucket for decades. States up and down the east coast experience the same dangers for recruitment and retention of bay scallops.  In North Carolina, the bay scallop harvest has decreased to essentially no landings because of recruitment failure resulting from a red tide event in 1987, several hurricanes in the 1990’s, and cownose ray predation.  Hopefully with good planning and excellent science, we can avoid that here.

Bay scallops are filter feeders and eat plankton (which could include some inadvertent cannibalism) in the water column.  Siphons bring water over a filtering structure, where food becomes trapped in mucus.  Next, the cilia on the structure move the food toward the mouth. Then, the food is digested in the stomach and digestive gland. Waste is passed on through the intestine and exits via the anus. Like many filters feeders, if there is something dangerous in the water, a scallop is rarely going to be able to avoid that or selectively feed. Sometimes due to a combination of factors, the algae species present can “bloom” or increase rapidly in numbers, tinting the water and causing adverse impacts.  The phenomenon is not that different from the way cancer cells multiply in tissue: something triggers a beneficial growth situation, introducing more food, a change in temperature, or something else metabolically advantageous that causes these organisms to multiply out of control.

The term “red tide” is usually used by lay people to refer to any number of large explosions of algae populations.  Oceanographers and marine biologists use the term “harmful algal blooms” (HABs) to refer to large outbreaks of algae that release toxins that can be concentrated in creatures which ingest algae, or can cause fish kills and other adverse effects.  In New England, and more specifically Massachusetts, red tide was relatively unknown until 1972.  According to the Massachusetts Division of Marine Fisheries (Mass-DMF), during the fall of 1972, Hurricane Carrie slowly passed through the Gulf of Maine during a massive toxic algal bloom in the Bay of Fundy.  The counter-clockwise winds intensified the traditional water current patterns and deposited red tide dinoflagellates known as Alexandrium fundyense/ tamarense, along the Maine, New Hampshire and Massachusetts coasts.  This was the beginning of the red tide menace in the Bay State. (

There are many things that can endanger a scallop population.  Storms that occur the two times a year when scallop larvae are in the water (late spring and early fall) can send scallop larvae out of the bay and into the ocean where greater water depths and less suitable substrate exists to support them. Storms can also stir up silt and sediment that can choke out the gills and filtering apparatus of the scallop.  Winter storms like Nor’easters push seed and adult scallops onto shore.  Nantucketers are especially responsive and almost heartbreakingly willing to gather together on bitter cold mornings after large storm events to scoop up the scallops and return them to the safety and relative warmth of the water.  Even persistent northerlies (winds from the north) can stack scallops like sea foam on the beaches on the southern side of Nantucket Harbor.

Coastal planning efforts, whether in the harbor as part of the Nantucket and Madaket Harbors Plan ( or in state and regional planning efforts for coastal waters, often is concentrated on protecting resources like eelgrass beds while allowing boaters, fishermen, docks and other public and private access to exist. The balance between all these users or stakeholders is key, and protecting natural resources while allowing fair use can be tricky, but extremely gratifying when all the pieces fall into place. The Town of Nantucket is extremely proactive and professional in their stewardship of the bay scallop populations. Our shellfish biologist, Tara Riley and her team of assistants have significantly upgraded the shellfish hatchery, providing super productive and efficient phytoplankton grow rooms to feed the millions of tiny scallop larvae that they grow out into juvenile scallops that can be successfully released. A quick summary of some of their work can be found on their website:  “Due to increased environmental pressures and limited funds, the Town of Nantucket’s Marine and Coastal Resources Department implemented a new program in 2010 to evaluate releasing competent hatchery-reared bay scallop larvae into pre-selected areas in an effort to increase the chance for larval retention and survival during optimal tides and conditions. Currently, the town has gone from releasing 5 million competent larvae in 2010 to releasing 170 million in 2012.” – See more at:

As one of the action items in the Nantucket and Madaket Harbors Action Plan, island fishermen, scientists, and conservation experts worked together to create a overarching document for protecting and enhancing our scallop fishery called the Shellfish Management Plan ( or SMP, link at bottom of article). Many of those SMP volunteers are members of the Nantucket Shellfish Association which advocates for the scallop fishery and healthy habitat and educates the public at their popular Scalloper’s Ball. You can also have fun and learn about our maritime heritage and the scallop fishery at the Maritime Festival held this year on Saturday September 21st and co-sponsored by the Egan Maritime Institute and Remain Nantucket The island community contributes oversight and advice on issues relative to the harbors and fisheries with the volunteer elected Harbor and Shellfish Advisory Board chaired by Peter Brace ( .

During the past few years a more worrisome alga has been showing up in the upper and middle harbor as far west as the field station harbor front in Quaise. This is the infamous rust tide caused by the dinoflagellate (small unarmored 2-8 cell organism with flagellas or little whip like tails, cute but deadly) called Cochlodium polykrikoides. The filter feeding scallops ingest the dinoflagellate in the water column, which although it does not kill the scallop, leads to decreased body mass weights.  Think of it as trying to eat healthy veggies and proteins and only finding watermelon to eat.  In Japan and Korea, this dinoflagellate has been blamed for fish kills and is often called a “red tide” organism. It is different from the Brown tide organism (Aureococcus anophagefferens) which almost completely decimated the bay scallop population in Peconic Bay (Long Island) in 1985. Of course, until you get these critters under a microscope, they all look the same! This summer, even though we had an abundance of spring rain that tends to be the harbinger for harmful algal blooms, the rust tide has not yet shown up in the harbor. It sometimes is more evident in late August as the water heats up and nutrients from septic systems and fertilizers slowly accumulate. The cloudy weather this summer has kept blooms from setting up and as we upgrade our septic systems and fertilize more thoughtfully and responsibly nutrient concentrations will diminish in the water column.

University of Massachusetts Dartmouth’s School of Marine Science doctoral candidate and beloved Nantucket Marine Biology teacher, Val Hall has been working on the dynamics of the scallop spawn and population for several years. She has been collecting data on the range of sizes and age classes of scallops in the harbor and working to determine the significance of the fall spawn scallop (aka, nubs) to the overall health of the bay scallop fishery. She also presented a talk on spat bag deployment and observations and information on rust tide which can be found here:

There is probably no single plant more important to our harbor ecosystem than eelgrass.  We have relatively healthy beds of eelgrass in both harbors and in shallow areas around the island and the islands of Tuckernuck and Muskeget.  The protection of eelgrass habitat is critical in order to have a viable bay scallop fishery.   Eelgrass (Zostera marina L.) is a subtidal marine angiosperm (flowering plant), or “seagrass,” that grows in temperate waters, often forming extensive underwater meadows.  It is not seaweed, but actually an underwater submerged grass that flowers and primarily spreads via rhizomes or roots. Eelgrass beds are highly productive communities, and are ecologically important because they act as a nursery, habitat, and feeding ground for many fish, waterfowl, and invertebrates.  Eelgrass beds, as well as other seagrasses, often have become the center of resource management initiatives to protect them.  Eelgrass meadows build up in the spring and summer, and then decay in the fall and winter.  Eelgrass blades can grow up to 3 or more feet long. They are found in relatively shallow subtidal habitats and rarely are found much deeper then twelve feet.

Buzzards Bay National Estuaries program eelgrass expert, Dr. Joe Costa has been studying and diving and restoring eelgrass in the Cape Cod area for many years.  In addition, the Commonwealth of Massachusetts and Dr. Charlie Costello have been mapping the changes in eelgrass around the state for many years ( with local support from the Nantucket Field Station.  For the past few years field station interns have been doing underwater surveys of the nearshore areas in front of the Field Station and in various locations around Nantucket to evaluate eel grass coverage.

Some key stressors that can knock out an eelgrass bed include the blockage of light due to high sediment levels resulting from land erosion.  High nutrient levels, caused by the excessive use of fertilizers, runoff and sewage outflow indirectly affect grasses by allowing excessive algae to grow both in the water and on the grass blades, further blocking the necessary light.  Boat propellers and impellers have torn rooted vegetation out of bottom sediments and dredging has caused severe scarring of underwater grass beds.  Back in the 1930s, eelgrass beds up and down the Atlantic coast were decimated by a disease called wasting disease.

The UMass Boston Nantucket Field Station and the UMB School for the Environment in collaboration with the Egan Institute will be hosting a renowned bivalve researcher and shellfish aquaculture advocate, Dr. Sandra Shumway, at a public talk Thursday August 15th at 7:00 pm at the Coffin School at 4 Winter Street. Dr. Shumway even has a type of marine phytoplankton named after her! I would love for any creature to be named after me, a not so subtle hint to any biologists reading this article.

“Dr. Shumway’s research spans over 25 years in shellfish biology, filter-feeding, physiological ecology of marine invertebrates. After post-doctoral studies at the University of Otago, New Zealand and the Department of Ecology and Evolution at SUNY Stony Brook, Shumway spent 11 years as a research scientist with the State of Maine Department of Marine Resources and as an adjunct scientist at the Bigelow Laboratory for Ocean Sciences. Shumway pioneered the study of impacts of harmful algae on shellfish and introduced the use of flow cytometry as a means of determining particle selection in filter-feeding invertebrates. Her primary research focus has been on problems directly applicable to industry needs, e.g. distribution of toxins in individual shellfish tissues, detoxification rates, and timing and extent of toxicity between bivalve species with the goal of establishing species-specific closures. Most recently, she has been working in collaboration with scientists from North Carolina State University to determine the potential impacts of Pfiesteria a spp. on shellfish and public health. Most recently, a new species of dinoflagellate, Pfiesteria shumwayae, discovered by Drs. JoAnn Burkholder and Howard Glasgow, was named in her honor.

Dr. Shumway is a strong advocate for the shellfishing industry and regularly attends working group sessions and meetings with fishermen as an invited advisor. In early 2000, she organized and co-chaired the National Shellfish Workshop, a forum sponsored by the Cooperative Research and Information Institute designed to develop a National Shellfish Plan. Dr. Shumway is very active in the National Shellfisheries Association and was the first and, thus far, only woman to serve as President in its 95 year history” (from retrieved August 12 2013).

More information:

Shellfish management plan:

Portions of this article were previously published in Yesterday’s island back in 2011 and can e found in the archives: and

Articles by Date from 2012