ANCHORAGE, Alaska – Alaska’s rare coral gardens will be protected under a new federal rule setting large areas of the sea floor off-limits to bottom trawling.

The new rule protects 370,000 square miles of ocean floor from bottom trawling, making it the largest protected marine habitat in the United States. The rule takes effect July 28.

Under the rule, more than 320,000 square miles in the Aleutian Islands – or an area approximately the size of Texas and Colorado combined – will be protected from bottom trawling. The other 50,000 square miles are in the Gulf of Alaska.

The ocean floor being protected includes six small areas, totaling just 126 square miles, where federal scientists in 2002 discovered coral gardens scattered along the Aleutian chain.

The cold water coral gardens, similar to those found in the tropics, have been observed nowhere else, according to the National Oceanic and Atmospheric Administration.

“This is the first time something like this has been found so far north,” Jon Kurland, NOAA’s assistant regional administrator for habitat conservation, said Thursday. “What was very unusual here was having so many different species growing together in one space, almost like a garden.”

Once disturbed by fishing gear, the cold water corals are slow to recover.

The rule, adopted by NOAA Fisheries, stems from a lawsuit filed by environmental groups in 2000, said Jim Ayers, vice president of Oceana, the main plaintiff. The discovery of the coral gardens strengthened their case, he said.

“Here is this beautiful animal performing this incredible function on the sea floor that takes hundreds of years to grow and develop and can be destroyed instantly by these bottom trawls,” Ayers said.

In the Gulf of Alaska, 10 areas along the continental shelf will be closed to bottom trawling to protect hard ocean bottom that may be important to rockfish.

Five small areas in Southeast Alaska also will be closed to bottom contact with fishing gear to protect dense thickets of red tree corals. Another 15 areas offshore will be closed to bottom fishing to protect seamounts, which are underwater peaks that provide important habitat to animals living at varying depths.

While describing the rule as “tremendous,” Ayers said 40 percent to 50 percent of coral areas in Alaska are still open to bottom trawling.

Environmentalists had long warned that coral beds, sponge gardens and seamounts will be ruined without more protection from bottom trawlers. The trawlers, many of them out of Seattle, scrape the ocean floor with weighted nets in search of species including Pacific cod, Atka mackerel, black rockfish and some flatfish.

Bottom trawling is already off-limits over more than 100,000 square miles in the Gulf of Alaska and Bering Sea.

The rules were not expected to do major harm to the commercial fishing industry because most of Alaska’s billion-dollar bottom-fish harvest occurs on the continental shelf spanning the Bering Sea.

However, the rule will have a large impact on the bottom trawlers that works the Aleutians, said Dave Benton, executive director of the Marine Conservation Alliance, which represents about 80 percent of groundfish and shellfish harvesting in Alaska.

Trawlers in the Gulf of Alaska will be far less affected, he said.

The alliance worked with NOAA and the North Pacific Fishery Management Council to distinguish the areas that needed to be protected, Benton said. Skippers got out their maps and provided information on where they fished and where they knew there were corals.

Benton said the fleet, for the most part, was already steering clear of the corals.

“We recognize it will cause the fleet some difficulties,” Benton said. “On the other hand, we recognize you have to protect important habitat.”