Abstract: A tissue extract containing a low molecular weight, non-proteinaceous compound selected from the group consisting of (A) methanol-soluble compounds obtainable from Leptogorgia virgulata with R.sub.f values in reverse-phase, thin layer, silica gel chromatography of (1) 0.42, 0.54, and 0.62; (2) 0.35, 0.50, and 0.58; (3) 0.37, 0.47, and 0.58; or (4) 0.31, 0.43, and 0.54, respectively, in 1:1:1 methanol:ethyl acetate:water, 2:1:1 methanol:ethyl acetate:water, and 1:2:1 methanol:ethyl acetate:water, or (B) methanol-soluble compounds obtainable from Renilla reinformis with R.sub.f values in thin layer, silica gel chromatography of (1) 0:44, 0.37, and 0.53; (2) 0.52, 0.42, and 0.60; (3) 0.56, 0.43, and 0.63; or (4) 0.32, 0.26, and 0.37, respectively, in 9:1 chloroform:acetonitrile, 9:1 methylene chloride:acetonitrile, and 4:1 methylene chloride:acetonitrile and compositions containing the same, which is useful as antifouling compositions, is disclosed.