Life Under Ice

by Pat Jaquith
pat@westvalleynaturalists.org

Cliff Lake ice receding 4.09.17

I’ve never given much thought to what goes on in a pond once it freezes, but this year I have made some discoveries that will have me looking at that environment with new interest.

Water Boatman under the ice Cliff Lake 12.03.21

We’d had cold temperatures, but no snow, and the ice on Cliff Lake was thicker than a pane of glass in early December when I was there. While it was tempting to tap on it to see how strong it was, better judgement prevailed, and I contented myself with taking some pictures of the patterns in the ice. To my surprise, this Water Boatman swam into view! Thus started my new interest.

Water Boatmen are small insects common world-wide, and are considered native to Montana. They feed on algae, microscopic insects, plant detritus and other materials at the bottom of their aquatic home. Fish, ducks and other birds feed on them. As adults, they have wings and fly over the surface of water and even from one watery habitat to another. They are dependent on air to breathe; even under the ice, they can collect a bubble around their body and swim with it for several hours, even to the bottom of the pond

Water Boatman 10.17.18 Cliff Lake, showing front legs and the large rear legs that are used for ‘rowing’
Water Boatman’s eyes are triangular, on either side of face. It may be rowing toward the Diaptomus (the small brown creature with prominent feelers) at right 10.17.18

These photos were taken through the ice on Cliff Lake in December. Daphnias, also called ‘water fleas’ for their jumpy movements, are tiny (1/10inch) cold-blooded freshwater crustaceans that spend most of their daytime at the bottom of the water to avoid predators and come to the top at night to feed on phytoplankton (mostly algae). Their transparent covering makes it possible to see the heart, digestive system, and its (one) dark-colored compound eye. Fish and other water organisms feed on them. Their presence in a body of water is considered a sign of a healthy environment.

The Glassworm, that transparent light gray colored organism above, is monstrous (3/4 inch) compared to the Daphnia, one of its food sources, along with mosquito larvae. They are the larval form of Phantom midges that resemble mosquitoes and are seen in swarms near water.
The four black cylindrical objects in the body are “hydrostatic organs” – like swim bladders that keep them stable in the water. The protrusions from the head are modified antennae used to grasp their prey.

The Diaptomus (the creature that the Water Boatman may be eyeing hungrily in the image above) is about .08 inch long is reported to be rarely seen in winter. An aquatic micro-organism that feeds on bacteria, algae, and other small organisms, it is an important food source for aquatic insects and small fish.

I’m always up for a new adventure in learning about our environment. If you have found something that fascinates you or that you have a question about, I’d love to hear from you!

Leave a Reply

Your email address will not be published.