Laboratory-reared barnacle larvae Balanus amphitrite were used in settlement assays to isolate and partially purify barnacle settlement inhibitors from extracts of sea pansies, Renilla reniformis. Settlement inhibitors are specific low molecular weight substances. Active
substances absorb in the UV and cannot be stained with phosphomolybdate. They have relative mobilities on silica in 9:1 methylene chloride/acetonitrile of 0.3 to 0.55. The region with a mobility of 0.55 has an EC50 of 0.5 mg of original material/ml and is the most potent. Relative
mobilities of inhibitory substances on reversed phase thin layer chromatography developed with 3:1 acetonitrile/H2O range from 0.45 to 0.65. Substances with mobilities between 0.45 and 0.55 contain the major inhibitory activity. This active material has an EC50 of <2.5
μ/ml. Settlement inhibitors from R. reniformis are different than settlement inhibitors from whip corals Leptogorgia virgulata (Rittschof et al., 1985) in chromatographic properties. Potency (mg original basis) of inhibitors from sea pansies is 10-fold higher than potencies
of inhibitors from whip corals.
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