Breathing in Climate Change: International Collaboration to Study Sea Scallops in a Changing Environment

In September 2024, my colleague Shannon Meseck and I took a road trip up north to Canada, to visit a research lab in St. Andrews, New Brunswick. The St. Andrews Biological Station is a part of Fisheries and Oceans Canada, the Canadian equivalent to NOAA Fisheries. Though the oldest of Canada's Atlantic research facilities, the lab features state-of-the-art seawater systems with capacity to do climate and aquatic research.

This project was a transboundary collaboration with climate scientist Helen Gurney-Smith to study climate change stressors on Atlantic sea scallop larvae. It was funded by the NOAA Ocean Acidification Program. The larval period, typically the first 3 weeks of a sea scallop's life, is particularly challenging for bivalve shellfish because they are planktonic, or free-floating in the water column. During this period, larvae are subject to heavy predation and are transported through ocean currents. The water they are exposed to is constantly changing with environmental conditions, and pulses of warm and/or low pH water are becoming more common with climate change.

One way we can test how larvae respond to changes in environmental conditions is by measuring their respiration rate. As with all animals, sea scallops breathe oxygen and release carbon dioxide. The oxygen they breathe is dissolved in seawater, and we can measure the drop in the oxygen concentration of that water over time with specialized equipment known as respiration chambers. Changes in respiration rate indicate physiological stress. We hypothesized that respiration rate may change when sea scallop larvae are exposed to non-ideal seawater conditions.

While in Canada, we performed three experiments to answer three questions:

1. How do larvae raised in current conditions respond to sudden changes in pH?
2. How do larvae raised in current conditions respond to sudden changes in temperature?
3. How do larvae acclimated to different pH water respond to heat wave conditions?

Measuring respiration in microscopic larvae is no small feat! We had to use specialized equipment that can measure the oxygen concentration in water from multiple replicates and sample treatments at once. The key is to fill each well with enough water to not stress the larvae, but not so much that it will take days for the larvae to deplete the oxygen. In each glass plate that we used, 24 samples and/or blanks can be run at once, and the volume each sample well holds is less than 1/10 of a milliliter. We carefully added the larvae to the wells and sealed them to prevent any additional air from dissolving into the water. Then we placed the wells onto the electronic oxygen readers which measured how much oxygen was present in each well every 15 seconds for 8-16 hours.

Dr. Gurney-Smith and her technician Erin Miller successfully spawned sea scallops in early September, so we had plenty of 2-week-old microscopic larvae to work with. Picking the animals out in groups of 10 for each well took a lot of effort, however! Each larvae was about ⅕ of a millimeter, or about the width of a human hair. It takes a lot of dexterity and a steady hand to pipette live larvae off of a slide under a dissecting microscope!

To answer our second and third research questions, we needed a way to control the temperature of the entire apparatus, so we used specialized water baths with continuously flowing seawater. We adjusted the seawater to one of three temperatures:

• Current conditions: 57°F (14°C)
• Near-future warm: 66°F (19°C)
• Severe heat-wave: 75°F (24°C)

While the apparatus is designed to go into these water baths, we struggled to control leaks, get the flow rate correct, and maintain heated seawater at a steady temperature. The whole team held our breath during overnight readings, hoping that nothing would leak and destroy the electronic equipment. Thankfully, the system held together well, and we were able to successfully complete all three experiments during our time in Canada.

The next steps of this collaboration are to analyze the data and see how the scallop larvae responded to the different treatments. The temperatures and pH levels we chose for this experiment represent ocean conditions expected in the near and distant future. The results will also serve as a snapshot of how larval sea scallops may respond to sudden changes that are becoming more and more frequent, including marine heatwaves that create a pulse of warm water to which the animals must adjust.

As a part of this international collaboration, some of Dr. Gurney-Smith's team will visit us at the Milford Lab next year to help with our ongoing surfclam ocean acidification work. They will introduce us to technologies they use in the Canadian lab that we can apply to larval Atlantic surfclams here in Milford.

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