ABUNDANCE, EFFECTS AND MANAGEMENT OF EPIPHYTISM IN INTERTIDAL CULTURES OF GRACILARIA (RHODOPHYTA) IN SOUTHERN CHILE

The control of algal epiphytes is a major technical problem for the expanding Gracilaria culture activity in southern Chile. Both harvestable biomass of Gracilaria and epiphytes show marked seasonal variation. In the spring months, epiphytism by Giffordia sp. can be very high (up to 300% of the Gracilaria biomass), the epiphyte forming a dense algal turf over its host. During the summer, Ceramiales are the dominant epiphytes, but abundance is significantly lower (P < 0.01) compared with Giffordia. Epiphytism can significantly (P < 0.05) affect Gracilaria production, and harvesting during a period of high Giffordia infestation can significantly increase (P < 0.05) the negative effect of the epiphytes. The use of higher algal biomass has no significant effect on the abundance of Giffordia. A Gracilaria inoculum obtained from a subtidal culture center was more susceptible (P < 0.05) to epiphytism than an inoculum from an intertidal area. In addition, the use of sand-filled polyethylene tubes to plant Gracilaria beds can promote the fixation of Giffordia in some cases.