Young Scientists Go to the Zoo
Armies of youngsters were making a traditional spring trip to the zoo when I visited one day last week, but around 250 of them were high school students bent on serious scientific investigation. They were there to study macroinvertebrates in an event sponsored by the Bronx River Alliance.
Scientists study macroinvertebrates in streams – insect larvae, aquatic worms, little crustaceans and such — because they provide food for fish and because the type of macroinvertebrates found in a particular river or stream indicates how healthy the water is.
I learned a little about them and got a preview of the event, Macroinvertebrate Day, when I dropped in on a meeting of a Bronx River Alliance Education Team a few weeks ago. There I found teachers delicately probing around in bundles of decaying leaves that had been marinating in a stream upstate. The leaves had been placed in the stream because macroinvertebrates like to eat decomposing matter and would be lured inside the leaf packs.
The teachers gently teased wormlike crane fly larvae and tiny stone fly larvae out of the leaves with little brushes and carefully spooned them into plastic petri dishes where the larvae could wiggle around in some water. One teacher excitedly located a leech. For Macroinvertebrate Day, bundles of leaves would be placed in the Bronx River so the students could follow the same procedure to find out which of the little critters are living in the Bronx.
The number and type of macroinvertebrates in a river are indicators of water quality. When the teachers found crane fly larvae in the leaf pack from the upstate stream it was a good sign because crane flies can’t survive in polluted water. In polluted water, only more resistant species can survive. At the teachers’ meeting I wondered: Will the students find crane flies in leaf packs from the Bronx River?
At Macroinvertebrates Day there were several activities introducing the students to the lives and habits of invertebrates. In a food web activity, students made an actual web by tossing a ball of yarn from student to student. Some of the students represented decaying leaves, some represented crane flies, may flies, stone flies, caddis flies and other macroinvertebrates, some represented fish or birds. Through the web thus created, the facilitating teacher taught about a food chain where plants (decaying leaves) furnish food for small animals (macroinvertebrates) that in turn are eaten by larger ones (fish and birds).
In another activity, students got a picture of how macroinvertebrates indicate water quality. Where there is pollution or loss of habitat, an animal has only three options: It can move, adapt or die (MAD). The activity demonstrated that since macroinvertebrates cannot move out of polluted waters or quickly adapt to them, pollution will kill them off. It led to the conclusion that if macroinvertebrates die off because of pollution, so will all the other creatures that depend on them for food.
After these and other introductory activities, the students were seated at tables where they were given leaf packs where they could hunt for living macroinvertebrates. I was eager to find out which ones the students would find in the leaf packs that had been soaking in the Bronx River. In the dishes I examined, they did not find any crane flies or stone flies or leeches. They found tiny shrimp-like creatures called scuds. Finding scuds indicates that the Bronx River is not the sewer it was for many years, but, though greatly improved, it’s still not in the condition of the cleaner upstate waters.
Later in the day, the students walked along an interpretive trail in the zoo. There they were to keep an eye out for a beaver that has recently been spotted swimming in the Bronx River. Beavers are also a biological indicator because they can’t survive in severely polluted water. I later learned that two groups actually did spot the beaver, near the “twin dams” area. I missed it on Macroinvertebrate Day, but maybe I’ll get back to the zoo another time to take a look.