Evidence from 12-Year Study Links Ecosystem Changes in the Gulf of Maine with Climate Change

Evidence from 12-Year Study Links Ecosystem Changes in the Gulf of Maine with Climate Change


East Boothbay, Maine - With half of Maine’s largest rainfall events of the century occurring in the past seven years, researchers at Bigelow Laboratory for Ocean Sciences and the U.S. Geological Survey have documented evidence of significant changes in the Gulf of Maine ecosystem directly tied to increased amounts of rainfall and volumes of river discharge.

A century of climatological data and river flow data, plus results from the Gulf of Maine North Atlantic Time Series (GNATS), provide the strongest connection yet between changing conditions on land affecting coastal ocean productivity.

Published in the Marine Ecology Progress Series (Vol. 450:11-25, 2012), the data show a large shift downward in primary productivity, with a five-fold decline in the growth rate of phytoplankton—­‑the microscopic, single-celled plants that form the foundation of the marine food web and ultimately support the Gulf’s fish and lobster populations. The researchers note that the impact of this decline could take several years to affect the food supply of commercial fish species, however, since the phytoplankton serve as food for larval fish, several years in advance of their harvest as adult fish.

“The Gulf of Maine has been the recipient of extraordinary amounts of runoff from land over the past few years, traceable to changing rainfall patterns over the last century. While the reasons for this dramatic decrease in marine primary production are complex, the ramifications are not particularly complicated,” said Bigelow Senior Research Scientist Dr. Barney Balch, the lead author of the study. Co-authors are Bigelow scientists David Drapeau and Bruce Bowler, and USGS Research Hydrologist Thomas Huntington.

Increased river discharge appears to be preventing deep, North Atlantic water -- which carries silicate and other nutrients essential for phytoplankton growth -- from entering the Gulf of Maine through the Northeast Channel. This is causing significant changes in the Gulf’s biogeochemistry. At the same time, greater runoff from rivers has led to an increase in the amount of detritus and colored dissolved organic matter in the water, reducing the amount of light available for phytoplankton photosynthesis and growth.

“You can’t drop the primary production of an ecosystem by a factor of five and not have an impact on other parts of the marine food web that depend on it, such as fish or lobsters,” Balch said. “Way back in 1924, Henry Bigelow -- Bigelow Laboratory’s namesake -- used the epithet ‘All fish is diatoms,’ which he paraphrased from the biblical passage, ‘All flesh is grass.’  He was making the connection that the productivity of fisheries is related to the microscopic plants on which the fish larvae ultimately feed. The extraordinary decrease in primary production we’ve documented here could become a stark reminder of Bigelow’s insightful words.”

As part of this same study, temperature and salinity data were compared to measurements taken along the same transect beginning 35 years ago by other scientists, including Dr. Charles Yentsch, founding director of Bigelow Laboratory.  The results show statistically significant increases in surface temperature in the Gulf, as well as decreases in salinity.  The increase in sea surface temperature (0.018°C yr−1) is considered a moderate rate of warming and is consistent with global increases in ocean temperature reported by other researchers.  The decrease in salinity (–0.0087 PSS yr−1) is greater than changes observed by others further out in the mid-Atlantic, presumably due to the Gulf’s proximity to freshwater river sources.  Such long-term salinity decreases can be caused by a number of climatological factors, including changes in the Earth’s water cycle and the melting of the polar ice cap.

An internationally known global ocean research center since 1974, Bigelow Laboratory for Ocean Sciences conducts research ranging from microbial oceanography -- examining the biology of the world’s ocean at the molecular level -- to the large-scale ocean processes that affect global environmental conditions.  Funded by the National Aeronautics and Space Administration, GNATS is the longest transect time series in the Gulf of Maine, documenting changes in nutrient concentrations, phytoplankton biomass, and carbon fixation between Portland, Maine and Yarmouth, Nova Scotia since 1998.