The Biology of the Stream

Abstract

Many biology instructors overlook the possibilities of a stream, especially a creek or brook, as a teaching aid. They suppose that running water represents a highly specialized environment, that the biology of the stream is too complicated for elementary study, and that the bulk of freshwater life is in the ponds and lakes instead of the streams. In coimiparison with other inland habitats, running water is actually rather broadly generalized, for even the most turbulent mountain torrent has some quiet pools and backwater areas. Adjustments of plants and animals to physical environmiental conditions are often nore obvious in running water than in still water or on land. If there is a streaimi near enough to be readily available for field observation it should not be neglected. The suggestions in this paper come from actual experiences of teachers and pupils fromn kindergarten to university, involving both plains and mountain streams. Any interested teacher can enlarge upon and modify them to fit any particular type of running water habi-' tats available in his own community. A small stream may be an important source of biological material for general observation, laboratory study, aquariuLm stocking or preservation for future use. Attached to stones and sticks in swift currents may be found various green algae and water moss. Water cress abounds in spring-fed brooks. Spirogyra and other filamentous algae, Euglena and similar microorganisms live in quiet pools back of large rocks, fallen logs and other obstructions. Arrowweed or arrow-head, reeds, spatterdock and cattails are to be found in side pools and cutoffs. Pondweeds sometimes occur in slow streams. Duckweed and other floating plants may be found in quiet pools and backwaters. Protozoa of many kinids occur in still pools and ainong attached algae in currents. Rotifers are frequently associated with them. Sponges are found on submerged sticks in clear cool streams. Hydras are common on vegetation growing in clear water in slow streams or pools in sunny places. In suitable locations they may be founLd the year around. Bryozoa are found on stones and logs in clear water, either in pools or in currents. They are not prominent in appearance anld are often overlooked. Planaria and similar flatworms are found attached leech-like to the bottoms of stones in moderate to swift currents. Their color often blends so well with that of the stones that they are easily overlooked. There are two common types of roundworms in streams. The almost microscopic nematodes are very generally distributed in slow muddy-bottom streams; the larger hairworms ( horsehair snakes) are found in clear water in pools or slow currents, generally in or above bottom vegetation. Annelids are also represented by two common types, bristleworms and leeches. The former are abuncdant in muddy bottomus and decaying vegetation; the latter are found in pools, on sticks and rocks in slow streams, and attached to turtles and frogs. Clams are generally buried in mud or sanid in the shallower parts of slow