They look like giant hair curlers stacked in a garage-size triangle. But they're actually prefabricated housing for fish - a new kind of artificial reef now being tested off the coast of Florida.
They're one of several new types of man-made reefs being spawned to make barren stretches of ocean bed more suitable for marine life. And, perhaps, to help commercial fishermen improve their catches, too.
Reefs also are being made now from old bridges and discarded oil rigs. All are part of a renewed thrust in the United States to improve and add to the more than 500 artificial reefs that dot the ocean floor off the country's coastlines.
Artificial reefs - in the past made of old tires, appliances, and even trolley cars tossed into the sea - have long been used to enhance marine life. They act as magnets for small fish, which in turn attract larger fish. Eventually barnacles, crustaceans, and other plants and animals cling to the reefs, creating whole new ecosystems. In some areas, artificial reefs have increased local fish populations more than twofold within a few years.
But now marine scientists are using new materials and methods to make fish habitats that are cheaper, easier to use, more likely to lure fish - and less likely to wash up on someone's beachfront.
One area being explored: prefabricated fish habitats, such as the giant hair curlers. This new generation of fish ''shelters'' is largely borrowed from the Japanese, the world leaders in artifical reef technology. Many of of the new prefabs are larger and more mobile than those used in the past.
Several being tested in Florida are made of rust-free plastic and fiber glass. Unlike bulky concrete reefs, which usually have to be toted to sea on a barge, these are equipped with inflatable air bags, making them easier to whisk around. They are anchored with concrete.
Daniel Sheehy, president of Aquabio Inc., a marine research-and-development company testing the reefs, says they have proved more effective as fish habitats so far than some traditional cement structures. Widespread use of prefab structures, though, remains a few years off. Instead, the chief building blocks for fish shelters in the United States continue to be old scrap materials. They are usually cheaper and more abundant. But many items traditionally used, like appliances and old tires, can end up on beaches after storms.
Thus even here scientists are finding new answers. One of the best may prove to be discarded oil and gas rigs. Platforms in the Gulf of Mexico have long been known to spawn new marine ecosystems (provided there are no oil spills). But once a well is capped, the rigs are usually towed ashore and sold for scrap (by law they have to be removed once out of production).
Parts of two rigs now lie off the Florida coast. The first was tossed overboard in 120 feet of water in 1980; the second was sunk last September. Scientists say they are better fish habitats than many other scrap materials because they are taller and more open.
''Most fish won't go up into dark openings. They need to move in and out with the current,'' says Dr. Heyward Mathews, an oceanographer at St. Petersburg Junior College. ''An oil rig sticks up like a Tinkertoy.''
Some fisheries experts would like to see more rigs used as reefs. There's no lack of supply: Oil companies scrap some 40 rigs a year from the Gulf of Mexico alone. A chief snag, however, is who pays for any damage that might occur from the rigs, say, snagging a fishing net, and who foots the hefty bill to tow them into place? In the Florida experiment, the state has taken responsibility for damages.
To spur more reef building, sport fishermen and some others would like to see tax incentives given to companies that donate old rigs, construction rubble, bridges, and other materials. Still, some environmentalists caution that, without strict supervision, it could become a convenient way to use the ocean as a dumping bin.