Suppression of Laminaria sporelings by allelochemicals from coralline red algae

We investigated whether allelochemicals that could suppress other algae were released from the coralline red algae, Corallina pilulifera and Pneophyllum zostericolum, Bialgal cultures were composed of either of the two coralline species and Laminaria sporelings in a millicell-CM insert. Higher culture temperatures tended to increase suppressive activities of both coralline algae against female gametophyte maturation and normal sporophyte formation of Laminaria. Even if dissolved iron, which is known to be required for the gametophyte maturation, was amply supplied to PES medium, the suppressive activity was still recognized. In bialgal cultures, when C. pilulifera and L. japonica sporelings were horizontally placed, the suppressive activity decreased compared to those vertically placed. Suppressive effects against the female gametophyte maturation in the conditioned medium of C. pilulifera was apparently lower than those in bialgal cultures. These results led us to assume that allelochemicals released from the coralline algae suppressed development of Laminaria sporelings and that they were volatile and/or labile substances. Three kinds of volatile halomethanes known to be released from C. pilulifera: bromoform, dibromochloromethane, and dibromomethane, were examined for suppressive effects on the development of L. angustata sporelings. Bromoform at a concentration as low as 3 ppm apparently reduced the normal sporphyte formation. Dibromochloromethane and dibromomethane showed weaker toxicities; both halomethanes contain less bromine atoms than bromoform. However, since we could detect only extremely low concentrations of bromoform in the cultures of C. pilulifera, we came to the conclusion that the actual allelochemicals in the bialgal cultures could not be the above halomethanes.