Gulf of Maine and Beyond

Changing food webs in the Gulf of Maine and beyond

While there is a clear consensus among scientists regarding changing global climate, many questions remain about the full impact of this change. Scientists understand the basic process, in which greenhouse gas emissions lead to increasing carbon dioxide in the atmosphere, which traps heat and increases global temperatures (global warming). The impact of carbon as it cycles through the atmosphere and dissolves into the ocean, however, is still not fully understood.

The ocean plays a key role in the carbon cycle, and even has the potential to offset greenhouse gases by taking up carbon from the atmosphere (carbon sequestration) through phytoplankton photosynthesis. Phytoplankton are marine plants that are the base of the entire ocean food web and provide half of the oxygen we breathe through photosynthesis. In turn, phytoplankton sequester a quarter to a third of global carbon dioxide emissions from the atmosphere. As they die and sink to the ocean floor, they take this captured carbon with them, helping to keep our planet’s carbon dioxide level in balance.

Dr. Barney Balch and his post doctoral researchers Meredith White, Jason Hopkins, and Catherine Mitchell are working to better understand the movement of carbon as it cycles out of the atmosphere and into the food web. Balch and his team have been running the Gulf of Maine North Atlantic Time Series (GNATS) survey for seventeen years, which makes it one of the longest running transect time series of coastal phytoplankton productivity in the nation. The transects measure ocean chemistry, biology and optical properties to determine the abundance and composition of particulate and dissolved carbon in seawater samples over time. Balch and his team have documented evidence of significant changes in the Gulf of Maine ecosystem. The data show an 80 percent decline in the growth rate of phytoplankton, which indicates lower production of the critical plants at the bottom of the marine food web. Because phytoplankton are food for fish larvae, lower production by these microscopic plants could mean lower numbers of adult fish populations years from now. The researchers predict that the decrease in phytoplankton is due to increasing amounts of dissolved, humic materials leached from the soils into the rivers after rains and ultimately flowing into the Gulf (the analogy is like tea being steeped from a tea bag). This humic material blocks the same colors of light required by plants for photosynthesis from penetrating into the ocean, effectively shading the phytoplankton and preventing their growth. If trends continue, Balch’s team and their fellow investigator, Tom Huntington of the U.S. Geological Service in Augusta predict this form of soil-derived, humic carbon will increase ~30 percent over the next 80 years, potentially causing further problems for the productivity of the marine food web.

Similarly, Dr. Nicole Poulton, Director of the J.J. MacIsaac Facility for Aquatic Cytometry, provides ground truth data for the NASA satellites used by Balch and other scientists to understand the relationship between the color of the ocean as seen from space and the carbon distribution of microbes, including species composition and identification of other particles in the water. Using a flow cytometer aboard a research vessel, she counts the number of microbes in water samples at sea that determines biomass—the total mass of organisms within the sample. Her results help to verify the accuracy of satellite-based data, which is important for measuring and understanding the global carbon cycle.

SCIENTISTS ARE GENERATING DATASETS USED TO ASSESS CURRENT CONDITIONS AND MAKE PREDICTIONS ABOUT FUTURE ECOSYSTEM CHANGES

Dr. Pete Countway is also contributing to our understanding of the dynamics of ocean life by analyzing the seasonal changes in the genetic structure and diversity of microbial communities. He conducted sampling on a weekly basis over a two-year period at a coastal time-series station, a research site established 15 years ago by the Bigelow Laboratory Aquatic Cytometry lab. This project is revealing the extent to which grazing limits the timing and magnitude of specific types of phytoplankton blooms. Countway's work is helping to identify the organisms that feed on some of the smallest marine phytoplankton (< 2-3 microns), which are the first link in many marine food webs. The long-term sampling from the dock in West Boothbay Harbor is creating an increasingly important ‘biological baseline,’ given the current and predicted changes to environmental conditions in the Gulf of Maine.

Using datasets like those generated by Balch, Poulton, and Countway other scientists can make predictions about future ecosystem changes.Dr. Nick Recorduses ocean models and mathematical ecology to understand and predict what is happening in the ocean with a focus on the Gulf of Maine. Record is generating a model that maps where carbon entering the Gulf of Maine ends up—including the amount entering the food web, sinking, or being released back into the atmosphere. He is also modeling the distribution of the tiny copepod Calanus finmarchicus, a primary food source for many species from cod to right whales. Interestingly, the species has persisted and even thrived despite predictions that warming would force it out of the Gulf of Maine and further north. Record also has begun a program to monitor the increasing numbers of jellyfish in coastal Maine by developing a citizen science reporting tool to share sightings information. This research provides a more complete understanding of how carbon dioxide is impacting the Gulf of Maine, as well as how the changing climate is impacting certain species in the Gulf, from Calanus to jellyfish.

While Record focuses on developing a more accurate model of the tiny copepods in the Gulf of Maine ecosystem,Dr. David Fields is studying how young lobsters and copepod populations might be changing as a result of climate change. Fields’ research focuses on the effects of increasing temperature and increasing ocean acidity caused by the high levels of carbon dioxide in the atmosphere. He is currently researching how increasing acidity and temperature affect the copepod, Calanus finmarchicus, and its tiny phytoplankton prey, Emiliania huxleyi, whose cells are made out of chalk plates that are susceptible to increasing acidity. His findings suggest that the ability of Calanus to store fat is hampered by increasing temperature and ocean acidification. This lack of fat storage is important because fish and marine mammals, which rely on Calanus as a food source, need fat to survive the winter; if their food has less fat, then their ability to survive is reduced.

This collection of research taken together gives an integrated understanding of how changing carbon levels and temperature are impacting the Gulf of Maine over time, and it will help us better understand what might lie ahead.