It could also be extended to allow time to identify the two different species in the area. Allow another class period for plotting and discussing results. Before the trip, spend some class time talking about ecology and other concepts such as food chains and competition. This should indicate that most of the amphipods are located at the medium-aged kelp wrack. Students use a standard sample size such as one shovel full of sand.
Students count amphipods in the sand and record the data.
Divide the students into groups of three. So that the amphipods are not counted twice, each group will have a student performing the role of counter, recorder, or collector. Students plot data on a graph and discuss the results. See if students can tell the difference by the way they pile the sand. One species piles sand in a line in one direction, while another piles sand all over in a circle.