ASK A SCIENTIST
Question: What is the weakest animal in the world but has a big population?
Several weeks ago we discussed the strongest, least plentiful animal which we decided was the tiger. Now I would like to answer your second question, about the weakest animal with a large population.
The lower on the food chain a creature is, the larger its population will be. Therefore the most plentiful animals will be those near the bottom of the food chain. I'm sure you have noticed how many insects there are. Insects are very low on the food chain. Oceans have food chains as well and at the bottom of these are organisms called plankton. Plankton consists of plants and animals that are too weak to swim very well and must drift along in ocean currents. They range in size from microscopic organisms to large jellyfish. The plants are referred to as phytoplankton and the animals as zooplankton. Although some types of zooplankton eat other zooplankton, most eat phytoplankton.
Krill, a shrimp-like invertebrate about six centimeters long, is the most plentiful zooplankton. There is likely a greater mass of Antarctic krill that any other species on earth. It is estimated that there are 100 – 500 million tons of krill in the Southern Ocean. In the Antarctic summer, krill can form swarms of up to 30,000 individuals in one cubic meter of water. Many animals take advantage of this abundant food source. Fish, squid, seals, penguins and other birds are among the many creatures that eat krill.
Perhaps the most surprising animals that depend on krill are whales, or more specifically baleen whales. Instead of teeth, baleen whales have two parallel rows of baleen plates. These plates look like gigantic combs. The whales swim with their mouths open, bringing in a large amount of water filled with krill and other organisms. They then use their tongues to squeeze the water back out through the baleen plates, but anything in the water such as krill is filtered out by the baleen and swallowed.
Only one kind of baleen whale, the bowhead whale, remains in Antarctica year round. Six other species migrate to tropical waters in the winter to give birth and raise their young in warmer water. But there is not much food for them there because tropical water lacks the nutrients that phytoplankton need in order to survive. So the whales return to Antarctica when the ice recedes in the spring and summer. Antarctic waters are very rich in nutrients due to the mixing of cold Antarctic water with warmer waters from further north. Krill are plentiful as a result and the whales are able to eat enough of the small creatures to fatten up for their winter migration.
Ask a Scientist appears Thursdays. Questions are answered by faculty at Binghamton University. Teachers in the greater Binghamton area who wish to participate in the program are asked to write to Ask A Scientist, c/o Binghamton University, Office of Communications and Marketing, PO Box 6000, Binghamton, NY 13902-6000 or e-mail email@example.com. Check out the Ask a Scientist Web site at askascientist.binghamton.edu. To submit a question, download the submission form(.pdf, 460kb).