Improved Plate Assay for Antifouling Substances Using Blue Mussel Mytilus edulis galloprovincialis

An improved plate assay for screening antifoulants against blue mussels, Mytilus edulis galloprovincialis, was designed based on an assay contrived by Ina and colleagues. To obtain more reliable results, the number of test mussels for one sample was increased from 4 to 10. Cardboard pieces used as test plates were cut into rectangular shapes to separate the test sample and the blank zone, which are of the same area. Activity was expressed numerically. In this improved method, several inhibitors of byssus thread formation were isolated by using a smaller amount of sample per area than in the original method. Previously our laboratory developed a foot-stimulating bioassay for the same purpose. This method requires only a small amount of sample and is therefore useful for isolating antifouling substances from natural sources, including marine organisms. However, the inhibition of byssus thread formation cannot be directly evaluated in the foot-stimulating method. The improved plate assay and the foot-stimulating method were examined and compared using a secosterol from the sponge Dysidea granulosa and CuSO(4).