North Carolina's Offshore Shipwrecks Have Surprising New Tenants-Tropical Fish

North Carolina isn’t known as a hotspot for tropical fish, but a new study suggests scuba divers should give the waters off the state’s coast a second look. A new study published in the journal Nature Communications Biology finds that shipwrecks and other structures serving as artificial reefs in deeper waters provide habitat for tropical fish in the northern reaches of the range, and may give these species some refuge as climate change alters reefs to the south.

Scuba-diving research ecologists from NOAA and Duke University conducted species counts at 30 natural and artificial reefs off the coast of North Carolina four times a year between 2013 and 2015. They found that the number and diversity of both tropical and subtropical fish was greater deep in the artificial reefs. At the naturally-occurring reefs, which are typically found in shallow water, temperate species were common.

It’s the depth of the artificial reefs that matters, says Avery Paxton, a marine ecologist at NOAA and Duke University Marine Laboratory, in a press release.

“We didn’t see these patterns on artificial reefs at shallow or intermediate depths, we only saw them on deep reefs, located between 80 to 115 feet below the surface, where water temperatures often experience less seasonal change,” says Paxton.

Why the fish are attracted to these deep artificial reefs is hard to say at the moment. “It could be that the zooplankton and smaller fish these species eat are more plentiful on artificial reefs,” study co-author J. Christopher Taylor, a NOAA marine ecologist, says in the release. “Or it could be that human-made reefs’ complex structures give the fish more nooks and crannies where they can evade predators. We’re still trying to figure it out.”

Whatever the case, the finding could have big implications for how conservationists prepare for climate change. Many studies have found that as ocean temperatures tick up, fish are moving towards the poles, with tropical fish beginning to colonize temperate waters. That trend is expected to continue as climate changes. The artificial reefs in North Carolina and other places could act as refuges or stepping stones for tropical species as they move northward.

Carrie Arnold at National Geographic reports that artificial reefs are actually quite common. Since the 1800s, people have dumped junk in the ocean to create structures for fishing. More recently, humans have deployed structures intentionally to create artificial reefs, including old cars and outdated military equipment — after scrubbing them of any potentially harmful chemicals, of course.

In fact, North Carolina has a program dedicated to creating artificial reefs that has 42 artificial reefs in the ocean and 22 in estuaries. Besides those reefs, North Carolina’s coast is known as “The Graveyard of the Atlantic,” with around 2,000 shipwrecks strung along its coast. Many of those wrecks serve as artificial reefs as well. Just last month, another study showed that those shipwreck-reefs are important to sand tiger sharks, an endangered species that might use the wrecks during its annual migration.

But building artificial reefs is becoming more sophisticated than just scuttling an old ship. Some researchers are experimenting with plastic and silicon reefs that mimic some of the coral species that are disappearing due to ocean temperatures in places like the Mediterranean to give some of the fish species that rely on them a place to survive. Studies like this one could help researchers decide where exactly to deploy new reef technologies.