Evaluation of repopulation techniques for the giant kelp Macrocystis pyrifera (Laminariales)

In Chile, the brown alga Macrocystis pyrifera has been subject to strong harvesting pressure, resulting in severe reduction of natural beds, and a threat to the sustainability of the resource. Repopulation is a possible means for the recovery of overexploited natural populations of M. pyrifera. In this study, we determined density (ind. cm(-2)), length (mm) and biomass (g) of M. pyrifera sporophytes sown on three types of substrata (ceramic plates, pot scrubbers, clam shells). In laboratory experiments, sporophytes on ceramic plates were significantly longer than those on pot scrubbers or shells after 60 days, and their density was also higher. Juvenile sporophytes seeded on the three substrata were transferred to the sea and placed either inside or outside a M. pyrifera forest. At the end of the experiment in the sea under the kelp forest, highest biomass and length were obtained on the clam shell substrates, but the density did not show significant differences between the substrates. However, outside the kelp forest, no significant differences in kelp density or length were observed between the three substrates tested; but the biomass was significantly higher on the clam shells than on the other two substrata. We conclude that the installation of kelp seeded substratum units may be an option for recovery of exploited M. pyrifera forests.