<p>Oil from the Gulf of Mexico spill is making a "real mess" out of sensitive salt marshes, such as this state-owned reserve pictured July 3, 2010, near Grand Bay, Alabama, one scientist says.</p> <p>That's because the oil may slowly poison marshes that are critical nurseries for the majority of the Gulf's marine life, including shrimp and commercial fish, according to William Finch, a senior fellow with the Washington, D.C.-based nonprofit the Ocean Foundation.</p> <p>What's more, marsh ecosystems have less resistance to oil, which—once it's carried inland with the tide—tends to stick around longer in the low-lying wetlands, said Finch, a longtime Alabama conservationist.</p> <p>"You're not going to see sudden death in this marsh—you're going to see things so screwed up that the marsh will die over the next year or two."</p> <p class="MsoNormal">—<i>Christine Dell'Amore </i></p>