A student washes a Clarke-Bumpus plankton net at Lake Titicaca, Peru. This sampling apparatus can be towed vertically, horizontally, or diagonally to strain zooplankton and phytoplankton from the water. A meter in the front of the net measures the amount of water that has been filtered so that researchers can calculate the density of the plankton. Lake Titicaca's zooplankton community is dominated by calanoid copepods (Boeckella spp.).