The twins used Taimina’s formula for some time, but monotony took its toll. “One day Christine shouts, ‘I’m sick of mathematical perfection!’ and started making her stitches more random, which made the pieces look a lot more organic,” says Margaret. “Nothing in nature is ever perfect.”

In 2005, the pair started training a core group of 15—mostly conservationists who learned to crochet­—and a hobby blossomed into activism. Then it became something of an obsession: “These little fluffy things have taken over our lives; it’s like something out of ‘The Trouble with Tribbles’!” jokes Margaret. “We’ve got probably 3,000 models now.” The smaller, one-inch pieces can be completed in as little as 30 minutes, but larger models take substantially longer. (Christine has been working on one for three years.)

Both the art and preservation worlds have taken notice of the project, with institutions like Pittsburgh’s Andy Warhol Museum and the Chicago Cultural Center hosting exhibitions. A reef made of textile coral sewn by Windy City activists will be on display at the World Financial Center show, as will one crocheted by a group of 100 New Yorkers (some seasoned crafters, others new to the trade) and a yarn-and-trash model called the Toxic Reef. “People ask if this is art-and-crafts or science or consciousness-raising or a feminist statement. It’s all of that—that’s the beauty,” says Margaret.

Also on view in the Winter Garden is Helle Jorgensen’s Rubbish Vortex, a crocheted-plastic-bag representation of the Great Pacific Garbage Patch—a floating garbage dump that’s been accumulating man-made detritus in the middle of the Pacific Ocean since the 1950s. (It’s currently twice the size of Texas.) “Coral reefs are under stress—we’ve got to get the message of conservation out there,” says American Museum of Natural History marine biologist Kate Holmes, who will join Margaret at a lecture at the AMNH on Tuesday 8. “The crochet project takes a new and interesting twist by looking at the mathematics of coral. It’s another entrance point…and it allows us to involve craftspeople who might not be into conservation.”

Margaret is confident that with two New York shows and an upcoming exhibit in London, her and her sister’s efforts are resonating with an increasingly eco-conscious public. “The crocheted reef will have a long lifespan,” she predicts. “But let’s hope not longer than the reefs themselves.”

The Hyperbolic Crochet Coral Reef is on display at the World Financial Center Mon 7–Aug 31, 2008.