How Many Organisms

During the warm months of the year, ponds and the near-shore waters of lakes are usually teeming with organisms such as frogs, tadpoles, fish, water bugs, aquatic beetles, snails, and cattails. Hidden beneath the water and not as well known are the organisms that live in the mud and sediment at the bottom of a pond or lake. Tubifex worms, clams, mussels, crayfish, seed shrimp, flatworms, scuds, snails, insect larvae, and insect nymphs are some of the more common bottom-dwelling animals. In addition, many aquatic plants are attached to the bottom, and their root systems and holdfasts wind through the bottom sediments. The place where an organism lives, such as the bottom of a pond, is called its habitat.

A sampling tool such as a bottom scraper can be used to scoop up bottom organisms. Estimates of population density (the number of organisms per unit area) and organism diversity can be obtained by counting the numbers of organisms that are scooped up from a given area of bottom sediment.

Outdoor Biology Instructional Strategies (OBIS) is an outdoor program that offers young people fun and challenging opportunities to investigate ecological relationships in their local environment. OBIS was developed in the 1970s at the Lawrence Hall of Science to help adults (teachers, parents, community leaders) take young people outdoors to experience ecological principles in their local area. We have made several of the original 97 OBIS activities available digitally. These activities, which increase environmental awareness, can be used individually or in combination. These simple experiences then act as a gateway for children and adults to explore and understand their local environment.