Shawn Rodgers, age 10, of Bradenton, Florida, for his question:
What is sea lettuce?
Ordinary lettuce is the main ingredient in the salad bowl. Everybody knows that the leafy plants grow on the land. Some of us grow it in our gardens and even in window boxes. But nobody could coax it to grow in the sea. However, thousands of different plants to thrive in the salty sea. And one of them is a lovely seaweed that looks a lot like a leafy lettuce. Naturally, it is called the sea lettuce.
The problem of pollution is leading us to poke our noses into all sorts of places that we never noticed before. The sea, of course, was always interesting and we knew that there were seaweeds. Now we are told that marine plants and animals are harmed when certain pollutants are dumped into rivers and oceans. We become indignant and also curious to learn what harm is being done. After all, it is unfair to let our waste materials ruin living things in the sea. What's more, it also ruins the beauty of our seashores and even threatens the future of life on the land.
As we investigate these marine problems, we meet a lot of new plants and animals that we never knew were there. We learn that there are countless different seaweeds, large and small, and that each species thrives in its own zone of the sea. There are thousands of species and the teeming individuals are uncountable. Of course we knew that our oxygen is provided by the plant world, without charge. But many of us assumed that it came from the earth's green forests and meadows. A small percentage of it does. All the rest of the world's breathable oxygen is provided by the teeming seaweeds and wafted ashore by the breezes. This is why the pollution of ocean waters is a present and future threat to all life on the land.
The sea lettuce and other seaweeds are simple plants with no true roots or stems. Most of them are members of the huge algae clan, whose ancestors teemed in the seas long ages before some of their relatives rooted themselves on the land. Many larger algae prefer shallows, the sunlit waters near the shores. Here, in mild and tropical waters, we find the sea lettuce. This beautiful pale green alga is a wide rippling ribbon with ruffled edges. It may anchor a toe to the bottom while its frilly, four foot streamer waves gracefully to and fro with the sun speckled water.
Its neighbors include algae called sea grasses, feathery sea mosses and a sassy little tuft called a merman's shaving brush. This marine neighborhood is just beyond the tidal zone, in water about 30 feet deep. Here in the swaying currents, the algae soak up the sunlight to manufacture their own food and to contribute to the world's oxygen supply. Some are eaten by hungry fishes. Uncountable numbers of their single¬celled relatives provide the first link in the food chain that supports all life in the sea.
Ages ago, mankind discovered that some seaweeds are good to eat. Cattle thrive on certain seaweed fodder and almost every seaweed species is a rich fertilizer for the soil. Nowadays, at least 100 species are harvested for human food and one of these edible algae is the frilly green sea lettuce.