Most people visit Venice with basic essentials like a camera, a guidebook and smart togs for a romantic night out—plus maybe Wellington boots in the likely event the piazzas are flooded. But now visitors to the City of Love should also consider packing scuba gear. Ongoing work to construct artificial reefs and floodgates to keep Venice from turning into a modern-day Atlantis has produced an unlikely side effect: a fast-growing, underwater paradise with 250 species of flora and fauna, rivaling even the most teeming Caribbean dive spots.
This reef isn't coral; it is made of concrete and rubble, affording abundant nooks and flat surfaces for plants and crustaceans to grow. They in turn lure more fish to feed, benefiting the local fishing industry and creating an unusually vibrant and varied ecosystem for these waters. "We are surprised by the rapidity and strength of these new colonies," says Andrea Rismondo, a marine biologist who coauthored a study for the Society for the Ecology of the Lagoon and Coast. "It is amazing that we are seeing this sort of diversity and opportunity for diving in the north Adriatic."
In addition to providing a new scuba-diving venue, the Venice lagoon's accidental reef offers a valuable opportunity to study biodiversity as it develops. Rismondo says that invasive algae and foreign fish are doing battle against native species. And even fish commonly found in this area are reproducing more quickly and living longer. Not only that, thanks in large part to global warming, nonharmful species commonly found only in warmer waters are doing well in the ecosystem created by the artificial flood barriers and jetties. For the first time, the world's largest bivalve mollusk, the Pinna nobilis, normally found only in the Mediterranean Sea, is thriving in the Adriatic. The mollusk survives only in good-quality water—a clear indicator of the health of the sea in this area, despite the potential for pollution from the ongoing construction. Also now present in this part of the Adriatic: the giant medusa, a 60-centimeter jellyfish never before seen in these waters. Commercial species are also multiplying, from edible oysters to a new, permanent biomass of nearly 600,000 kilograms of mussels—more than double what existed less than a decade ago.
But the news isn't all good for Venice's marine biology. With the massive population explosion of friendly fish and fauna, there is also a proliferation of dangerous species. Rismondo says alien algae have taken over the natural seabed and spread into the lagoon—both the areas that run through the city of Venice and those in the outlying areas tourists rarely see. Their long, brownish strands are visible in the canals and often get tangled in the vaporetto boat engines. City authorities now dredge up nearly 1 million metric tons of the stuff each year from the canals to prevent it from rotting in the shallow water. Manila clams and Pacific oysters have also invaded the area in recent years.
Most of the foreign species are introduced accidentally when commercial ships empty their ballast water into the harbor. But because of the ample underwater life, they quickly take over. The native species eventually either learn to coexist with them or surrender and die out. Already several species like the Dyspanopeus sayi crab have all but disappeared from the lagoon and sea, smothered by foreign algae. "This is not the first time that human construction has provided a refuge for wild creatures," says Fulco Pratesi, head of World Wildlife Fund Italy. "Oil platforms often become a sort of paradise for anemones and oysters after a few years of use."
Still, similar reefs built on Italy's other coasts have not produced the same explosion of underwater life. The lagoon may be unique because most of the sea around it has been manipulated for centuries, creating a very unnatural environment, says Rismondo. Breakwater jetties were first built between the Adriatic Sea and the Venice lagoon in the 18th century in an attempt to smooth the effects of the tides and keep the sea from inundating the islands on which Venice is built. Those efforts have always kept Venice safe, if only marginally. But in recent years, rising seas, more-frequent storms and the physical sinking of Venice's landmass have all put the city at greater risk. Even with the floodgates, most studies predict that Venice won't stay above water for more than another 100 years. "The idea that the Venice lagoon is being manipulated only recently is absurd," says Rismondo. "In reality, Venice has been manipulated for centuries." If the latest efforts can't save Venice from sinking into the sea, scuba diving may eventually become the best way to see the city.