Critters in the Connecticut

Celia Chen, Ph.D. and her daughter

In June 2003, Center for Environmental Health Sciences staff introduced a group of aquatic "macro-invertebrates" to local residents who attended the annual Connecticut Riverfest "Big Splash" in Wilder, VT. Along with Dartmouth ecologist Celia Chen, CEHS outreach summer interns Audrey Campbell (Dartmouth '02) and Bethany Fleishman (St Lawrence University ’03) put together an interactive exhibit featuring live insects and several species of minnow collected north of Dartmouth in the Connecticut River. Microscopes provided visitors a face-to-face encounter with crayfish, dragonfly larvae, and the tiny aquatic animal, Daphnia. Visitors were encouraged to try to identify insects. The purpose of the exhibit was to educate the community about the role that aquatic macro-invertebrates, or non-microscopic invertebrate organisms such as aquatic larval insects, mollusks, and crustaceans, play as bio-indicator species.

Aquatic organisms as bio-indicators

Scientists can monitor the general health of an aquatic ecosystem by using organ- isms that are particularly sensitive to environmental contamination. In the Connecticut River, populations of these bioindicator organisms decrease in response to poor water quality, particularly the presence of environmental contaminants and low oxygen content. Many aquatic insect larvae, such as mayflies, caddisflies and stoneflies, as well as Daphnia, are effective bio-indicators. A high number of these sensitive species can indicate a healthy river — one that has a high oxygen content and a low level of pollution. Low numbers of sensitive species and a high number of pollution-tolerant organisms may mean that the water quality is poor. This indicates that fish, other river organisms and ultimately humans may be exposed to pollution as well. Many bio-indicator species are important food sources to fish and waterfowl, so their decreased numbers can have an impact on fish. The importance of these small insects in the food web makes them vital to the health of the river.

Daphnia: sentinel species

The water flea Daphnia, an important part of the food web in lakes and ponds, is considered a "sentinel" species — an indicator of ecosystem health. Dartmouth scientists are identifying molecular biomarkers, minute but measurable physiological changes in these sentinel organisms that indicate a stress such as exposure to a toxic metal. These subtle changes in Daphnia may provide an early warning system indicating potentially toxic effects of polluting chemicals. The goal is to develop specific biomarkers that can indicate organisms are being affected by such toxins as mercury and PCBs. Understanding how small organisms such as Daphnia are exposed to and affected by pollutants will shed light on how humans will be affected.

To view and print a pamphlet that describes common aquatic species, "Critters in the Connecticut," click here. The document will open as a pdf file.

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