After storm, ocean floor reconfigured

When Hurricane Irma rolled across the Florida Keys this fall, it wasn’t just the motels and marinas, Tom Thumbs, stilt houses, and shell shacks strung along the island chain that got slammed.

Underwater, the storm pushed around massive amounts of sand, uncovering ancient reefs and burying some closer to its path. Some channels got filled, others reconfigured. Buoys that marked navigation or provided moorings for boaters got ripped free — some 800 alone in the Florida Keys National Marine Sanctuary will need to be surveyed. Debris, from boats to fence posts to propellersnagging utility lines, created new underwater hazards.

Navigation, never easy among the mud banks and seagrass flats or maze of islands, took on new challenges.

Now the Sanctuary that stretches from the north end of Biscayne Bay to the Dry Tortugas is teaming with the boating industry to undertake the daunting task of mapping the changes. Beginning Jan. 19 through February, the sanctuary is asking boaters to report changes to Navionics, an Italian company that produces navigational charts. Navionics also helped chart changes in the northeast after Superstorm Sandy.

“We cannot get all the information we need by ourselves. So we need to work with partners,” said Florida Keys National Marine Sanctuary Superintendent Sarah Fangman, who oversees a staff of less than three dozen, including a six-man buoy team responsible for about 2,800 square miles.

For mariners, changes after a storm are par for the course, but Irma was a Category 4 storm that made landfall, and the first to hit the Keys with such fury since Donna crossed Marathon with 140 mph winds in 1960. Hurricane-force winds stretched 160 miles. Tropical storm winds reached 440 miles. After Irma crossed Cudjoe Key, before and after satellite photos showed a dramatic bright halo of water clouded with sand all along the coastline, from the Treasure Coast to Cape Coral.

Much of the damage underwater reflected the damage above ground, with the worst impacts near Big Pine in the Lower Keys, and to a lesser degree, Marathon to Key Largo, Fangman said. Areas around Key West and Boca Chica suffered less damage, along with Key Largo to the north.

Damage to marine life, and especially the imperiled reef tract, which has shrunk to half its original size and battled disease and warming waters in recent years, is still being assessed. The sanctuary is working with Everglades National Park,