ASK AUDUBON

By Carolyn Shea

Which has more biodiversity, a coral reef or an artificial reef?

-Grant Wahlig, St. Louis, Missouri

When they built the first recorded artificial reefs two centuries ago, the Japanese uncovered a secret of the seas: If you sink it, they will come. Under the right conditions, a foreign object dropped into the ocean acts like a biotic magnet, attracting all manner of aquatic life. Like submerged condos, constructed reefs provide the scaffolding upon which marine organisms can colonize, and find food, shelter, and a place to spawn.

Jonathan Carlson

Some research suggests that artificial reefs harbor at least as much biodiversity as their natural counterparts, which are among the richest ecosystems on earth. Over the past two decades, manmade reefs have been deployed around the globe--with increasing frequency and varying results--to enhance fishing and scuba diving, protect shorelines, mitigate damage to natural reefs, even improve surfing conditions. More than 1,700 such "deployments" dot the waters off Florida alone. But these prefab habitats are not without controversy. Created by a hodgepodge of items, from rock and specially designed concrete structures to so-called "materials of opportunity"--scuttled ships, oil rigs, highway rubble, tires--they often come under fire for being little more than ocean landfills (see "Sea Urchins Ride the A Train," page 20). Depending on their composition, they can drift, erode, and pollute. It remains to be seen whether they can survive the multiple onslaughts, from overfishing to coastal development to global warming, that have compromised most natural reefs. "Nature is generally very resilient," says Paul Boyle, deputy director of the Wildlife Conservation Society's New York Aquarium, "if we stop the insults."

Why don't sharks get cancer?

-Norman Stoddard, St. Louis, Missouri

Sharks do get cancer, contrary to popular opinion and a best-selling book (improperly titled Sharks Don't Get Cancer) that sparked a feeding frenzy for their cartilage, the part of their anatomy reputed to fight the disease. Research has documented dozens of tumors in sharks (and in their kin, the skates and rays), including those of their cartilage. Some scientists hypothesize that the tissue may inhibit the growth of human tumors, although this remains clinically unproven. Apart from misleading the sick, claims that sharks hold out a cure have had devastating effects on the fish themselves. According to the World Wildlife Fund, 100 million are killed annually to support a worldwide trade in shark products, including pills made from pulverized cartilage. During the past 400 million years, sharks have evolved into apex predators--they occupy the top of the pelagic food chain. Without them, the links unravel. Ecologists suspect that intensified shark fishing in Australia led to collapses of the spiny lobster industry because octopuses, no longer eaten by the sharks, were able to prey unchecked on the lobsters. Says Gary Ostrander, a biologist at Johns Hopkins University, who was part of a team that found tumors in sharks, "You may not like them, but there's going to be a huge shift in the balance of the ecosystem if they're removed from it. We just don't know the outcome."

What good is poison ivy anyway?

-Brendan Klee, South Orange, New Jersey

Anyone who has scratched his or her way to recovery from an encounter with Toxicodendron radicans can be excused for giving the most obvious response: "None!" The bane of legions of allergic individuals, this widespread plant leaves many a soul apprehensive about ever having an out-of-doors experience again. Brushing against the least of its parts (or burning them) unleashes a resin spiked with urushiol, the nasty agent responsible for inducing itchy inflammations, oozing blisters, and sometimes anaphylactic shock.

Jonathan Carlson

Alongside its cousins, poison sumac and poison oak, poison ivy ranks as a leading cause of contact dermatitis in the United States, giving rise to 2 million reported cases a year. This toxic trio also lies at the root of most workers' compensation claims and a heck of a lot of calamine lotion sales. Despite its bad rep and ill effects--on humans and some primates but apparently not on other animals--poison ivy does have redeeming value. Many birds eat its berries. Deer browse on its leaves. Bees pollinate its flowers. Several Indian tribes enlisted poison ivy as a poultice; others made arrow poison from its sap, which has also been manufactured into indelible ink. The Dutch use it to reduce dike erosion. It has even graced floral arrangements and been cultivated as an ornamental-presumably by the immune. "Not to say people should grow it," cautions Steven Clemants of the Brooklyn Botanic Garden. "Unless, of course, they have neighbors they don't like."