Fun with Science Club®


			The story of the periwinkle and the wrack. Carrie Straight 05.25.01 Sea living animals use chemicals in the water to help them learn when predators are nearby. Aquatic prey animals send out some chemicals that occur only when a predator attacks them. This is beneficial, because other individuals of the same species can recognize the chemical and know to be on the lookout. Scientists have reported this type of induced response in terrestrial plants, but not in aquatic seaweeds. Gunilla Toth and Henrik Pavia studied a seaweed called knotted wrack (Ascophyllum nodosum) and the animal that eats wrack, flat periwinkle (Littorina obtusata). They placed some knotted wrack into aquaria and put 5 periwinkles per wrack into 10 of the aquaria. Wracks produce a chemical that spreads through the water when periwinkle grazes on it. The researchers took water from the tanks where the periwinkles grazed on the wracks and placed it into tanks that contained only the seaweed. The researchers predicted that by doing this manipulation they could get the wrack receiving the water from the other tanks to respond to the chemicals in the water and start producing a defense chemical (a chemical that the periwinkles don’t like the taste of). The researchers discovered that the seaweed does respond to some chemical cue in the water from the tanks with the periwinkle and the wracks, but they do not know if the chemical cue comes from the periwinkle or the wrack.


			Toth, Gunilla B. and Henrik Pavia. 2000. Water-borne cues induce chemical defense in a marine alga (Ascophyllum nodosum). Proceedings of the National Academy of Science 97(26): 14418-14420.