KANEOHE, Hawaii — Hawaii officials on Thursday proposed a series of steps to fight coral bleaching that’s threatening the state’s reefs, including new marine protected areas, limits on fishing, and controlling polluted runoff.

Hawaii’s ocean temperatures have been rising, causing corals to expel algae they rely on for food. Vast stretches of reef have turned white over the past two summers, increasing the risk that the coral will get sick and die. Some already have.

Coral reefs provide habitat for fish and other marine life, scientists say, and severe or concurrent years of bleaching can kill coral reefs.

Bruce Anderson, the state Division of Aquatic Resources administrator, said addressing polluted runoff is difficult, noting it would cost millions of dollars to create artificial wetlands that would help control runoff.

Another idea is to ban lay gill nets that fishermen leave in the water. Anderson said these types of nets are harmful because they kill all the fish caught in them, not just the species targeted by the fisherman.

The state will hold public meetings on its proposals before any are adopted.

Warmer ocean temperatures bleached coral in Kaneohe Bay off Oahu in 2014. Last year, they bleached corals off the west coast of the Big Island and off Maui.