Atlantic Surfclams’ Response to a Changing Environment

Atlantic surfclams support an important commercial fishery in the Northeast United States. Landings were valued at nearly $41.7 million in 2022. They also improve water quality by removing excess nutrients from the water when they filter and consume plankton. Our research aims to understand how surfclams respond to changes in their environment. 

Our results will help the commercial surfclam industry, recreational fishermen, and the emerging surfclam aquaculture industry. Growers may use the information to inform site and broodstock selection.

Surfclam fishing grounds are already shifting because of ocean warming. They increasingly overlap with another commercially important species, ocean quahogs. We are investigating surfclam growth under different environmental conditions to understand how environmental changes may affect surfclam production. If surfclams grow more slowly under shifting environmental conditions, it may take longer for them to reach the minimum catch limit for fishing. Over time, widespread shifts in the size, location, and abundance of clams may require fisheries management to adapt. 

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We know from laboratory experiments that ocean acidification causes surfclams to feed less and grow more slowly. Our colleagues have developed models that simulate growth based on the results of lab experiments. Our goal is to determine how well the lab-based growth model predicts the growth of clams in the ocean. Preliminary field observations indicate that surfclam populations may already be adapting to changing environmental conditions. This research combines lab and field work and computer modeling to better understand surfclam biology and ecology. 

This research relates to mandates under the: 

• Magnuson-Stevens Fishery Conservation and Management Act 
• Federal Ocean Acidification Research and Monitoring Act 
• National Aquaculture Act of 1980 

With a team of shellfish biologists and chemists and access to surfclam populations across the region, NOAA Fisheries is best positioned to conduct this research. Our research hatchery also has the technical capabilities to modify carbon chemistry and raise larvae under different conditions.

What is Ocean Acidification?

The ocean absorbs about a quarter of the carbon dioxide released into the atmosphere from human activities. This changes water chemistry by lowering pH, which is called ocean acidification. Surfclams and other bivalves build their shells using calcium carbonate, which may be more difficult in a more acidic ocean. We are studying how ocean acidification may affect ecologically and commercially important bivalve species, including Atlantic surfclams.

What We Do

Our activities include:

• Characterizing the carbonate chemistry of Atlantic surfclam habitats
• Evaluating the role of the environment and genetics on the growth and development of Atlantic surfclams
• Assessing the interaction between food availability and carbonate chemistry on larval survival and gene expression
• Using real world data to validate a model of surfclam growth and reproduction under future ocean acidification conditions

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Validating the Model with Real World Data

NOAA Milford Lab scientists built a model that projects Atlantic surfclam growth based on water temperature and the partial pressure of carbon dioxide. This is a commonly used metric of ocean acidification. This model indicates that ocean acidification will decrease surfclam growth and reproduction by the year 2100, under the Intergovernmental Panel on Climate Change’s high carbon dioxide emission scenario. 

Now we are studying surfclam populations in their natural habitat to see how well real-world observations match these model predictions. We will use data collected in the field to make our growth model for surfclams more accurate.

Role of Genetic Differences

Although the Atlantic surfclam fishery is currently managed as a single species, there are actually two genetically distinct subspecies native to Massachusetts waters. Spisula solidissima solidissima thrives in deeper water offshore and along the northern and eastern coast of Cape Cod. This subspecies grows larger and has a longer lifespan than the southern subspecies, Spisula solidissima similis. The smaller subspecies thrives in areas with riverine influence and is more tolerant of warm water and lower pH conditions. 

In addition, genetically different populations of the northern subspecies Spisula solidissima solidissima live in coastal Massachusetts and New York waters. Preliminary analysis indicates these different populations may also grow differently. We are conducting experiments to determine if genetics plays a role in observed differences in growth and/or environmental suitability.

Study Methods

Study Locations

Transplant experiments are currently in progress with surfclams from Provincetown Bay in Provincetown and off of Gooseberry Island in Westport, Massachusetts. These experiments began in 2024 and will be completed in 2025.

From 2021 to 2023, we monitored environmental conditions in surfclam habitats at five sites on Cape Cod, Massachusetts:

• Barnstable Harbor
• Eel Pond, East Falmouth
• Sea Street Beach, East Dennis
• Cockle Cove, Chatham
• Provincetown Harbor, Provincetown

We conducted transplant experiments at three of these sites from 2022–2023:

• Eel Pond, East Falmouth
• Crowes Pasture Beach, East Dennis
• Provincetown Harbor, Provincetown

Research Questions

• Does temperature or carbonate chemistry of either the seawater or the water within the sediment affect the growth of surfclams?
• Do differences between the subspecies affect the relationship between environmental conditions and growth?
• How well do our lab-based growth models predict surfclam growth rates in the field based on the environmental conditions of their habitat?

Habitat Characterization/Environmental Monitoring

Surfclams spend most of their time burrowed in the seafloor. We sampled seafloor habitats and their associated surfclams monthly from 2021–2023 to find out whether their growth rates correlate with the sediment chemistry where they live. We collected seawater, water within the sediment, and surfclams at each of our five study sites. We collected water within the sediment from depths of: 2, 5, 15, and 20 centimeters. In each seawater sample, we measured:

• Carbonate chemistry (pH, alkalinity, and dissolved inorganic carbon)
• Temperature
• Salinity
• Food available for surfclams (Surfclams filter feed, so the food available to them is organic and inorganic material suspended in the water)

In 2024, we deployed data sondes near surfclam habitats to measure temperature, pH, dissolved oxygen, salinity, and chlorophyll concentration in Provincetown and Westport, Massachusetts, and Shinnecock Inlet, New York. The sondes will take measurements continuously every 15 minutes for 1 year.

Current Surfclam Population Monitoring

We are collecting adult surfclams from each of our 3 field sites once per season to monitor differences in growth and condition of surfclams living in different environments. We use clam rakes to sample clams from our two Massachusetts sites. The clams live in deeper water at our Long Island, New York site, so we use a clam dredging boat to collect adult surfclams there. We are measuring:

• Shell size
• Meat weight
• Gut contents (to understand what the animals ate)
• Gonad development
• Information on the population’s genetics

Transplant Experiments

Our transplant experiments will help define the role of the environment on growth compared with the role of genetic differences between populations and subspecies. From June 2022–2023, we conducted a transplant experiment to evaluate the growth of the northern subspecies in its native habitat compared with a habitat where only the southern subspecies lives. 

During the transplant experiment, we collected and tagged juvenile surf clams, also called seed, and placed them in cages to measure their growth over time. The cages were nylon mesh enclosures we call “clam condos.” During three sampling periods, we measured growth and monitored environmental conditions in each enclosure, including: 

• Carbonate chemistry
• Temperature
• Chlorophyll a
• Food availability

We also conducted biodeposition sampling to measure feeding rate and metabolism.

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We collected and exposed the northern subspecies of surfclams to the habitat of the southern subspecies. We added crushed shell, called “shell hash,” to the sediment in half of the clam condos. We hypothesized the shell hash would increase the pH of the seawater within the condos and increase clam growth.

We are currently conducting a reciprocal transplant experiment that started in September 2024. This experiment will compare the growth of two genetically different Northern surfclam populations that are found in Provincetown and Westport, Massachusetts. We transplanted surfclams from Provincetown to Westport and vice versa. We will monitor their growth over a 9-month period as well as measure the food availability and water quality.

Larval Ocean Acidification Challenges

We plan to bring adult surfclams from Westport and Provincetown, Massachusetts, into the lab to spawn and produce larvae during summer 2025. We will expose the larvae to several different pH and food conditions based on field site measurements and predicted future carbon dioxide concentrations in the ocean. In addition to survival and growth, we will measure the respiration rates of the larvae and differences in gene expression between treatments. 

We will repeat the laboratory spawning during summer 2026 and place the resulting larvae in confined cages in a natural seawater environment to monitor survival of larvae from different surfclam populations.

Collaborators and Partners

• Massachusetts Maritime Academy
• Town of Barnstable
• Town of Dennis
• Town of Chatham
• Town of Falmouth
• Town of Westport
• Provincetown Shellfish Commission
• National Academy of Sciences Research Associateship Program
• Martha's Vineyard Shellfish Group
• Massachusetts Department of Conservation and Recreation

NOAA Ocean Acidification Program provides funding for this project.

Contact Information

Principal Investigators/Project Team

• Matt Poach
• Katyanne Shoemaker
• Genevieve Bernatchez
• Renee Mercaldo-Allen
• Shannon Meseck
• Daniel Hennen
• Matthew Hare
• Kyra DeGroat (2024-2025)
• Emily Roberts (2021-2024)
• Barry Smith (2021-2024)
• Katie McFarland (2021-2024)

Mass Maritime Academy Project Team   

• William Hubbard
• Kristin Osborne
• Shannen Allen (2022-2023)
• Crystal Santos (2022-2023)
• Ben Tuttle (2021-2022)
• Grace Calvert (2021-2022)

Additional Student Involvement

• Emily Lekas (2024), Hollings Undergraduate Scholar, University of Richmond 
• Sammantha Moronta (2024), American Fisheries Society Hutton Scholar
• Jonathan Lim (2024), Science Communications Intern, Stony Brook University
• Martin Gonzalez (2023), EPP/MSI Undergraduate Scholar, University of California Santa Barbara

More Information

Surfclams in a Changing Ocean: Massachusetts Maritime Student Stories

How Will Atlantic Surfclams Fare in a Changing Ocean?

Current Research at Milford Laboratory

Species Directory: Atlantic Surfclam