September 8, 2013

What are these animals telling us?

Because they are sensitive to change, so-called ‘sentinel species’ can reveal a lot about the ripple effects of pollutants in our environment. And that, scientists say, serves as a warning about our own fragile future.

By North Cairn
Staff Writer

(Continued from page 2)

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Green crabs, like these found off Freeport, are considered a “sentinel species,” which can tell us a lot about the ripple effects of mercury, lead and other pollutants.

Gabe Souza/Staff Photographer

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Sentinel species in Maine

Explore how ocean scientists, ecologists and biologists are studying a wide range of “sentinel species” in Maine with our interactive species guide.

Being able to collate and interpret information that spans a continent and its oceans would represent a big step in a more comprehensive understanding of complex issues such as climate change, ocean acidification and various kinds of pollution.

But at a certain scale, the attempt to observe, collect and monitor information becomes “too big to grasp,” said Erika Latty, associate professor of botany at Unity College. Limiting the scope of the research to a sentinel species can actually enlarge understanding.

Consequently, researchers are paying attention to what befalls many creatures at the bottom – as well as nearer the top – of the food chain for signs of widespread change or ripple effects that might ultimately pose potential risks – or means of rescue – for humans.

One such bottom-of-the-food-chain creature is the marine copepod, Calanus finmarchicus, a tiny crustacean. It’s considered a sentinel species in the Gulf of Maine, because so many other fish and sea animals feed on it.

It is a conduit from single-celled algae to larger fish and marine mammals, said Pershing, at the Gulf of Maine Research Institute. It is an essential bridge in the Gulf of Maine’s productivity, providing more than three-quarters of the diet of forage fish and sustaining much of the food web in the open waters off Maine.

It thus plays a critical role in the health of herring, sand lance, mackerel and the North Atlantic right whale.

Jeff Runge, biological oceanographer of the University of Maine and Gulf of Maine Research Institute, has investigated the copepod’s abundance and distribution patterns to learn more about what makes the species so successful here. Marine researchers, along with fishermen, have observed that numbers of the crustacean vary significantly in inshore versus offshore waters, and from year to year, but scientists do not yet fully understand why. But the vast amount of data that have been collected, going back to the 1960s, Pershing said, may disclose patterns or causes that researchers otherwise might not be able to discern.

“We’re still figuring out how to use that information,” said Pershing. But early indications link water temperatures, salinity and productivity in these populations.

Paralleling this research in the Gulf of Maine, French scientists, using satellite data and climate-ocean models, predict that the warming of surface waters will shift the copepod north of the Gulf of Maine by 2050. No one yet knows whether the species will disappear from the area, as these models predict, or whether they will persist, sustained by cold water currents from the north.

But one thing is certain: Any changes in this creature’s numbers, distribution or health in the ecosystem could impact the entire food web that depends on it.

“Things are seldom changing in a linear manner,” said William “Barney” Balch, a biological oceanographer and senior research scientist at Bigelow Laboratory for Ocean Sciences in East Boothbay.  Balch studies phytoplankton, microscopic photosynthetic organisms that live just below the surface of both salt- and fresh water. In his work, “sentinel species are those that indicate a threshold change.”

Phytoplankton blooms, for example, have raised concern about what effect climate change is having on the traditionally colder waters of the North Atlantic and Arctic.

“When we see blooms of things, usually those are indicating a change in the environment or a pathogen,” Balch said. “And the frequency of blooming has gone up lately.”

As the number and kinds of studied species increases and broaden, “these little individual species begin to reverberate,” said Rinker, the Gorham institute director. Layer upon layer of data produces a more comprehensive picture of how the environment is faring under human pressure, and how humans may be affected tomorrow by what we’re doing today, he said.

The warnings coming from the animals seem clear enough, said Rinker. “All over the world we’ve been warning people: Something dark is coming our way.” Sensing that, he said, makes continued research on individual species ever more critical.

North Cairn can be contacted at 791-6325 or at:

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