We have all seen the devastation wrought in coastal Louisiana — marshes that remain so contaminated with oil three years on that they can’t support insect life, never mind sea creatures. Fortunately, marshes in coastal Alabama, Mississippi, Texas and Florida mostly escaped damage from the spill, protected by barrier islands and luck. Those marshes have continued their work powering the entire coastal ecosystem by nurturing the young of nearly everything that swims in the gulf. In fact, these marshes are the single biggest reason the gulf has rebounded as well as it has from the spill.

But the marshes are in decline across the gulf. They have been for decades, the result of levee construction, the channelization of rivers, dredging, erosion and development. It is estimated that more than 50 percent have already been lost. Louisiana has been the most severely affected — the state’s coast has lost 1,900 square miles in the last 80 years — and even more will be lost, which makes the marshes in the surrounding states all the more important.

These marshes are our most valuable, and most vulnerable, coastal habitat. They can disappear beneath the developers’ backhoes in the blink of an eye. The recession derailed a lot of planned coastal development, much of it in the marshland fringing the gulf’s estuaries. As the economy ramps back up, those plans will be rekindled. Marshes will be turned into boat slips and condos, unless we protect them.

The Restore Act windfall represents a critical chance to grab up and safeguard some of the remaining marshes and coastal wetlands. If we don’t use a nickel of every Restore Act dollar to buy coastal lands, it’s a sure bet somebody will find another jail that needs a sea wall. Or, as happened in Alabama, a governor will propose building an $85 million hotel and conference center in a state park with money already provided by BP.