EXUDATES FROM GRACILARIA-CHILENSIS STIMULATE SETTLEMENT OF EPIPHYTIC ULVOIDS

Differences in susceptibility to epiphytes among algal species have be en explained traditionary on the basis of various defense and escape m echanisms. Gracilaria chilensis exhibits inter-strain differences to s usceptibility to epiphytes but such differences seem more related to s timulation of propagule attachment rather than to defense or escape me chanisms. Culture medium previously used to grow Gracilaria stimulates recruitment of Ulva and Enteromorpha compared to settlement (recruitm ent) in non-used growth medium. Elimination of bacteria from the cultu re media does not reduce the stimulatory effect. Chemical analysis of the culture medium indicates the presence of a mixture of polysacchari des consisting mainly of sulphated galactans, similar to those present in the water soluble fraction of agar produced by Gracilaria. Additio ns of various concentrations of soluble fraction of agar extracted fro m dry thalli of Gracilaria chilensis to SWM-3 culture medium results i n statistically significant increases in the density of settled spores of E. compressa and U. rigida.