Susceptibility of Atlantic Surfclams to Ocean Acidification

Atlantic surfclams support an important commercial fishery in the Northeast United States, with landings valued at nearly $30 million in 2019. They also provide environmental benefits, such as removing excess nutrients from the water, and are one of the largest bivalves on the East Coast. We characterize the seafloor habitats of Atlantic surfclams to understand their susceptibility to ocean acidification.

Surfclam fishing grounds are already shifting because of ocean warming, and increasingly overlap with areas in which ocean quahogs, another commercially fished clam, reside. We are investigating how climate change in the ocean may affect the size of surfclams. If surfclams grow more slowly under shifting environmental conditions, it may take longer for clams to reach the minimum catch limit for fishermen. Over time, widespread shifts in the size, location, and abundance of clams may require fisheries management to adapt.

We know from laboratory experiments that ocean acidification causes surfclams to feed less and grow more slowly, and our colleagues have developed models that simulate growth based on the results of these lab experiments. Our goal is to determine how well the lab-based growth model predicts the growth of clams in the ocean. This project combines lab work, computer modeling, and field work to develop a better understanding of surfclam growth.

What is Ocean Acidification?

About a quarter of the human-produced carbon dioxide released into the atmosphere is absorbed by the ocean. This causes changes to water chemistry, such as lowering pH, which is called ocean acidification. We are studying how ocean acidification may affect ecologically and commercially important bivalve species, including Atlantic surfclams.

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What We Do

Our activities include:

• Characterizing the carbonate chemistry of the seawater and sediment where Atlantic surfclams live
• Evaluating the growth of the northern and southern subspecies of Atlantic surfclam to better understand the role of the environment and genetics on the growth of surfclams
•  Clarifying the role of subspecies versus the environment on their growth
• Using real world data to validate a model of surfclam growth and reproduction under future ocean acidification conditions

Validating the Model with Real World Data

Milford Lab scientists built a model that projects Atlantic surfclam growth based on water temperature and the partial pressure of carbon dioxide, a commonly used metric of ocean acidification. This model indicates that ocean acidification will negatively affect 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 refine our growth model for surfclams, making it more accurate. 

Sampling the Porewater

We sample seafloor habitats associated with surfclams monthly to find out whether their growth rate correlates with the chemistry of the sediment in which they burrow. We call the water between sediment grains porewater. Scientists currently know much less about changes to sediment porewater chemistry than they know about the overlying waters, yet surfclams spend most of their time burrowed in the seafloor.

One Surfclam, Two Subspecies

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Although the Atlantic surfclam fishery is managed as a single species, there are actually two genetically distinct subspecies native to Massachusetts waters. Spisula solidissima solidissima thrives in deeper water off the northern 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.

The two subspecies may adapt to different sediment carbonate chemistry conditions in their respective habitats. We will use a transplant experiment to better understand the role of the environment and genetics on the growth of surfclams.

This information will help the commercial surfclam industry, recreational fishermen, and the developing surfclam aquaculture industry.

Student Involvement

Undergraduate students at Massachusetts Maritime Academy are providing field support for this project as they learn about shellfish biology and ocean acidification.

Study Methods

Study Locations

We are monitoring environmental conditions in surfclam habitats at five sites on Cape Cod, Massachusetts:

• Barnstable Harbor 
• Falmouth
• East Dennis 
• Chatham
• Provincetown

We are also conducting transplant experiments at three of these sites:

• Falmouth
• East Dennis 
• Provincetown

Research Questions

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

Habitat Characterization/Environmental Monitoring

We sample habitats and their associated surfclams monthly to find out whether their growth rate correlates with the sediment chemistry where they live. We are collecting seawater, sediment porewater, sediment, and surfclams at each of our study sites. Sediment porewater is collected from depths of: 2 cm, 5 cm, 15 cm, 20 cm. In each seawater sample, we measure: 

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

We also take sediment cores to measure grain size as well as organic and carbonate content. For each sediment sample, we measure: 

• Temperature
• Redox potential
• Percentage of organic matter
• Percentage of carbonates

Transplant Experiment

In spring 2022, we began a transplant experiment to evaluate the growth of the northern subspecies in their native habitat. We also evaluated the habitat dominated by the southern subspecies. Our research will help define the role of the environment on growth compared with the role of genetic differences in populations and subspecies.

We first collected surfclams last spring, marked them, and placed them in cages to measure their growth over time. The cages are 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, and chlorophyll a, a measure of food availability. We also conducted biodeposition experiments to measure feeding and metabolism.

We exposed each subspecies to two different substrates at each site. Half of the cages contained sediment from the site, half contained both site sediment and crushed shell—called “hash.”. We hypothesized that shell hash would raise the pH of the seawater within the sediment of the condo and increase clam growth.

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So far we have found that over the summer of 2022, clams at the Provincetown site grew much faster and had better survival than those at our East Dennis and Falmouth sites. We have sometimes measured differences in the pH between the shell hash and no shell hash treatments, but these differences are not consistent, so we’ll continue to collect more data. While we have not detected a significant effect of shell hash treatment on growth, more clams survived in the plots where shell hash was added at the Falmouth site.

During August 2022 we collected samples for transcriptomics, to look at differences in gene expression between surfclams kept in ambient sediment and those in sediment with crushed shell. Animals use their genome like a recipe book from which they assemble the many molecular machines and materials needed to grow and survive. To make proteins, animals must make copies of the genes in their DNA recipe book, a process known as transcription. These transcribed copies are then made into proteins. When animals are stressed, they often make additional proteins to protect against the new stressor. At the molecular level, this means they make more copies of the genes needed to make these proteins, or in other words increase the expression of certain genes. This work will explore whether surfclam gene expression differs depending on sediment pH. We will determine whether genes known to be associated with physiological stress, metabolism, and/or calcification are expressed more often in lower pH conditions.

Collaborators and Partners:

• Massachusetts Maritime Academy
• Town of Barnstable
• Town of Dennis
• Town of Chatham
• Town of Falmouth
• Provincetown Shellfish Commission
• National Academy of Sciences Research Associateship Program

NOAA Ocean Acidification Program provides funding for this project.

Contact Information

Project/Principal Investigators

• Matt Poach
• Barry Smith
• Renee Mercaldo-Allen
• Shannon Meseck
• Katie McFarland
• Daniel Hennen
• Emily Roberts

Project Team

• Mass Maritime Academy
  • William Hubbard
  • Kristin Osborne
  • Shannen Allen
  • Crystal Santos
  • Annemarie Kunkle
  • Blythe Stephenson
  • Ben Tuttle (2021-2022) 
  • Grace Calvert (2021-2022)

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