Coral Reef Conservation Reauthorization Act of 2018 This bill addresses the conservation and sustainability of coral reef ecosystems, including by reauthorizing and expanding the Coral Reef Conservation Act of 2000; authorizing the Department of the Interior to conduct activities to conserve coral reefs and coral reef ecosystems within national parks, national wildlife refuges, national monuments, and other federal land under its jurisdiction; authorizing Interior to offer financial assistance grants for coral reef conservation projects; establishing the Coral Reef Ecosystem Studies Program; directing the Department of Commerce to develop national guidelines for man-made structures that are suitable as artificial reef habitat for coral and other associated marine species; and ensuring that Commerce places an emphasis on stock assessments for fisheries associated with coral reefs.