Three new cembranoid diterpenes, knightine (1), 11(R)-hydroxy-12(20)-en-knightal (2), and 11(R)-hydroxy-12(20)-en-knightol acetate (3), were isolated as minor constituents of the Caribbean gorgonian Eunicea knighti, along with the known cembranoids 4-8. The stereostructures of the new compounds were determined by detailed spectroscopic analyses and a combination of chemical transformations and modified Mosher's methods. All isolated cembranoids were tested against fouling using a quorum-sensing inhibition (QSI) assay and a biofilm inhibition test. Compounds 2, 3, and 6 disrupted QS systems at lower concentrations than kojic acid and Cu(2)O, and in most cases cembranoids 1-8 showed bacterial biofilm inhibition at lower concentrations than kojic acid.