Seeking clues to change at the base of the food chain
RI EPSCoR research advances understanding of climate impact
Talk of climate change that resonates most with broad audiences typically hews to the big, noticeable shifts — increasing temperatures, intensifying storms, rising sea levels, and acidification of ocean water.
But before any of those scenarios play out, the foundation of change begins far from eyesight in the microscopic organisms at the base of the marine food chain.
Drifting in the columns of ocean water, subjected to the whim of currents, temperature and weather patterns, phytoplankton — the one-celled marine plants of the ocean — like their counterparts on land, carry out the finely tuned steps of photosynthesis. To grow, phytoplankton tap into the sun’s energy and convert carbon dioxide (CO2) and nutrients into organic matter while releasing oxygen into the water.
This process of generating plant material is called primary production. And, because of the ocean’s enormous size, these tiny organisms together account for as much primary production as all of the trees on land. If scientists can understand the factors that influence the primary production taking place in the ocean, they can better predict the response to climate change.
“The ocean absorbs a lot of CO2, not only through the balancing exchange of the gas between atmosphere and ocean, but also through phytoplankton, which by utilizing the CO2 dissolved in the water, can help draw it out of the atmosphere,” explains Françoise Morison, a newly minted Ph.D. in Oceanography from the University of Rhode Island Graduate School of Oceanography.
The carbon is then incorporated into the plant material, which provides food for other organisms and is the basis of most ocean food webs, Morison says: “Carbon is the currency we use to understand how energy flows in the food web.”
Among those studying the effects of climate change, Morison, a Rhode Island NSF EPSCoR-supported researcher, focuses on just one piece of the intricate process that influences the exchange of carbon and oxygen between ocean and atmosphere. She studies grazing patterns of protistan herbivores (the single-celled organisms that eat phytoplankton), their impact on how much phytoplankton is synthesized (primary production), and the factors that drive the variability of this impact.
“We generate these tiny puzzle pieces and, little by little, we understand more.”
To capture what occurs in the grazing process, Morison and others in her field measure the feeding rates — how much phytoplankton the grazers consume and what may influence how much they eat. The grazers’ role holds significance in the consumption of phytoplankton because some phytoplankton are too small to be eaten by larger organisms. In eating them, the grazers act as an intermediary, becoming prey for the next level of predator that otherwise would not have a food source.
Deceptively important because of the organisms’ microscopic size, this predator-prey relationship holds big implications for ocean health and future climate scenarios, according to Morison.
“How much the phytoplankton grow and become available as prey is important,” she notes. “They represent the base of the food chain in the ocean. If we didn’t have phytoplankton, we wouldn’t have fish. But the more the grazers eat and digest, the more CO2 they release back in the water, and the less CO2 the ocean can remove from the atmosphere.”
Although the object of Morison’s work involves the most minute details of the marine food web, the grazing of these tiny creatures yields a substantial impact. In compiling measurements taken from around the world to date, scientists estimate that grazers consume an average of 65 to 70 percent of all organic matter produced by phytoplankton.
“This is an average,” says Morison of the percentage. “And, it is an important one because as we try more and more to understand the oceans on a global scale and the impact of climate change, we need to use models that are fed these parameters. A model is only as good as the parameters we put in, so we need good estimates.
“However, there are limitations to the estimate of the grazing impact — it is based on the studies that have measured it at specific places and specific times, but there are gaps because it’s difficult to measure everywhere and all the time.”
Morison says scientists need to know how the percentage of organic matter consumed varies from the average rate. If they merely assume that one size fits all and use the average rate as a constant, the estimations may run over or under, which, in turn, would throw off the number figured into carbon budgets.
“For example, if 70 percent is consumed, that means a lot of CO2 is respired into the water column, reducing how much the ocean can absorb,” Morison explains. “At the same time, it fuels more carbon into the food chain. We need to know where the carbon goes in order to make better predictions.”
Building better methods
Questions remain about how these estimates may vary. For example, there could be a spatial variation based on where samples are taken from or seasonal influences from the time of year when the sampling occurs. Understandably, researchers typically conduct their work at sea during less volatile months as inclement weather restricts what they can do.
“My work addresses the variabilities and how we can go about resolving them,” Morison says, explaining why such details hold importance. “If we can improve our capacity to predict how the system may change and what kind of changes we might expect, then we can provide better information, which will hopefully serve to better prepare for climate change and manage resources.”
The standard method of collecting samples for measuring grazing is extremely labor intensive and limits scientists to processing one sample per day.
“We measure at one depth, at one point during the day,” Morison says. “We don’t have a good idea of how this percentage varies vertically, up and down the water column. We cannot presume that one measurement we make at 10 meters is the same as at 60 meters.”
The situation sets up the proverbial Catch-22: If scientists want to account for the variability of the measurements, they have to conduct more measurements; however, they can’t conduct more measurements because the process of doing so is too cumbersome. Morison says part of her research explores a shortened sampling method to inform researchers about the tradeoffs and quantify the consequences of using it.
Her dissertation also looks at the seasonal variability in grazing and considers whether more food availability means more consumption. Although this is usually believed to be true, Morison says, she found consistently low grazing across two seasons in Antarctica, regardless of how much food there was in the water.
This suggests to Morison that although phytoplankton grow faster in the light of springtime weather, the grazers don’t grow as fast, and their consumption fails to keep pace with the increased supply of food. Whereas this is due to year-round low water temperature or a slow feeding response after periods of starvation remains to be determined.
Still, what this finding means, at least in the Antarctic, is that grazers will not act as a check and balance to keep phytoplankton growth under control and prevent blooms. But at the same time, Morison acknowledges, these formulas don’t apply equally across the globe; other oceans in other climates may yield different results. Antarctica holds particular relevance in the quest to gain greater understanding because of the influence of climate change. The region is melting and the dynamics of the ecosystem hinge on the ebb and flow of ice formation.
Little is known about both vertical and seasonal variability, and vast areas of the world’s oceans remain unsampled, so these findings are critical, she says: “We generate these tiny puzzle pieces and, little by little, we understand more.”
For the third section of her dissertation, Morison utilized a piece of RI EPSCoR equipment, called a Flowcam, an instrument combining a camera and a microscope, to assess its ability to describe the variability of the marine community. Typically, this work has to be done with a microscope, which is a tedious and limiting process. In comparison, the capabilities of the Flowcam make for more efficient analysis of a greater number of samples.
Much like a vacuum, the Flowcam pulls the water sample in a stream across the lens and takes pictures at a much higher rate of speed than can be done with a microscope, cropping out plankton particles for identification and comparison of differences in composition of the community and in patterns of abundance. Together with improved sampling methods, Morison says these methods will help advance the body of science.
The work continues
Now a postdoctoral student at URI GSO, continuing to work in the lab of her Ph.D. advisor, Associate Professor Susanne Menden Deuer, Morison aims to publish some of the chapters in her dissertation as she steps into a role with the North Atlantic Aerosols Marine Ecosystems Study (NAAMES).
The NASA-funded project investigates the link between biological activity in the ocean and the formation of aerosols, the particles that come out of oceans and play a key role in the formation of clouds.The data collected will provide feedback on climate change, help develop the big picture, and improve the ability to predict how our climate might evolve and change, according to Morison.
She credits RI EPSCoR for providing research support during the pursuit of her Ph.D. — for one full year and two summers — which allowed her to make new discoveries: “Essentially, our ability to be there as a graduate student really depends on funding. You get some grants from your advisor, but you are always encouraged to find your own funding.”
Graduate students can apply for RI NSF EPSCoR support in the form of fellowships and travel to conferences to present their work for research that aligns with the RI EPSCoR mission. Awards often mean that students do not have to take time off from their research or assume a teaching assistant position, Morison says, which allows for full-time focus on their investigations.
Additionally, having access to RI EPSCoR equipment like the Flowcam played a critical role in Morison’s research. She took the imaging equipment on board for research trips, generating data for an entire chapter of her dissertation.
“The fellowship allowed me to do my research as a grad student in the best possible financial condition,” she notes. “The travel support is also important. I try to attend a conference once a year to present my work and communicate my results, and take advantage of the opportunities to network, get to know what other people are doing. Sometimes, the best ideas come from people in other fields.”
For Morison, who came to her Ph.D. journey later in life than many of her peers and earned her oceanography master’s along the way, the quest for new knowledge and understanding provides for a continuing adventure. The work does not end with the accomplishment of earning a degree.
“I don’t know if you’re ever all done,” she says, laughing.
Story by Amy Dunkle|Photos courtesy of Françoise Morison