<p>Marine biologist Paul Horsman of Greenpeace tramps through oil-clogged marshes on the east bank of the Mississippi River in <a id="sxrx" title="Louisiana" href="http://travel.nationalgeographic.com/travel/countries/?q=louisiana">Louisiana</a> on Monday.</p><p>After weeks of staying mostly at sea, the <a id="eyou" title="Gulf oil spill" href="http://news.nationalgeographic.com/news/gulf-oil-spill-news/">Gulf oil spill</a> is now washing up on the state's coasts—likely a devastating development, scientists say. (See <a id="w0g1" title="pictures of ten animals at risk due to the Gulf oil spill" href="http://www.tiehh.ttu.edu/ronald_kendall.html">pictures of ten animals at risk due to the Gulf oil spill</a>.)</p><p>As the nurseries for much of the sea life in the Gulf of Mexico, coastal marshes are vital to the ecosystem and the U.S. seafood industry, according to Texas Tech University ecotoxicologist <a id="b4g1" title="Ron Kendall" href="http://www.tiehh.ttu.edu/ronald_kendall.html">Ron Kendall</a>.</p><p>It's much harder to remove the oil from coastal marshes, since some management techniques—such as controlled burns—are more challenging in those environments, Kendall said on May 12.</p><p>"Once it gets in there," he said, "we're not getting it out."</p><p>—<em>Christine Dell'Amore</em></p>