Substantial amounts of Macrocystis and Lessonia are traditionally harvested and exported from Chile as raw material for alginate. Because of intense mari culture of abalone (Haliotis ssp.), herbivorous mol luscs that feed on brown kelps, pressure on local populations of Macrocystis and Lessonia has in creased to critical levels within the past 5 years, strongly supporting e¡orts to produce algae maricul tured biomass. Here, we present our results on the de velopment of new techniques for large scale kelp mariculture in Chile. We have abandoned the tradi tional technique of direct spore seeding onto inocula tion lines. Instead, we used gametophyte cultures that were manipulated to enter gametogenesis and to produce synchronous batches of 10 4 10 5 embryos.Juvenile sporophytes were cultured under perma nent aeration and agitation, £oating unattached in contamination free glass bottles up to 10 L, plexiglass cylinders and 800 L greenhouse tanks. When hold fast initials were formed at a size of 8 cm, the sporo phytes were spliced into Nylon rope fragments and transferred to the sea. Twelve months after initiation of gametogenesis in the laboratory, Macrocystis pyrifera attained14 m length and 80 kg fresh weight m À1 line in the sea. For Lessonia trabeculata 6 months after gametogenesis initiation, 0.25 kg fresh weight m À1was attained in the sea.

Two species of giant kelp inhabit the coast of Chile: Macrocystis integrifolia and M. pyrifera, representing important economic resources. As part of our efforts to domesticate these kelps for mariculture, and to obtain superior cultivars, we studied their biological relationship. Hybridization experiments with clonal gametophyte cultures showed reciprocal cross-fertility and produced fertile hybrid sporophytes with intermediate morphological characters. This hybridization potential in the laboratory contrasts with the persistence of two morphologically welldefined sister taxa in natural habitats on the Pacific coast of South America. We conclude that M. integrifolia and M. pyrifera are conspecific and speculate that unknown mechanisms support the coexistence of two morphologically distinct taxa on the subspecific level.

Macrocystis is an important marine resource in Chile, with severe problems of over-exploitation. Our study describes genetic materials and techniques for a further improvement of laboratory-based mariculture. For a systematic hybridization program we have selected one pair (cultivar) of gametophytes with favorable somatic and reproductive characteristics from each of seven localities in southern Chile. Sporophytes from all 49 crosses were grown for 10 weeks to seedling size. We report here that sporophytes from sympatric parents (intra-cultivar matings) grow to different length, depending on the locality and, importantly, that sporophytes from several inter-cultivar crossings show superior growth, suggesting heterosis with symmetric or asymmetric reciprocity. The genetic materials and techniques described here, together with our newly developed standardized seedling production protocols now available, constitute a significant step towards domestication of Macrocystis in analogy to terrestrial agriculture.

The kelps Macrocystis pyrifera (integrifolia morph) and Lessonia berteroana (northern lineage of Lessonia nigrescens) are intensely harvested in Atacama, northern Chile, for abalone forage and alginate production. Local situations call for simple restoration techniques for over-exploited kelp beds. We excised holdfast portions from parental specimens, including parts of stipes and phylloids. Untreated adult thalli and unmanipulated specimens served as controls. Fragments of both species were attached to boulders or rock platforms with elastic bands or cyanoacrylate glue. Transplanted fragments quickly formed new haptera, colonized new substrata, and reached reproductive maturity. Macrocystis regenerates increased in total length and holdfast diameter in one or both directions of the rhizome, forming a pair of stipes, followed by rhizome and haptera development. In Lessonia, tissue of non-injured zones took over new holdfast growth. Success of this propagation method varied with season and substrata. Both species proceeded to complete regeneration of holdfasts. However, holdfasts of older Macrocystis thalli partly decomposed, resulting in two apparently identical individuals. Advantages of these propagation methods are discussed in ecological and restoration contexts.

Recent progress in Macrocystis mariculture is based on clonal stock cultures of gametophyte parents. Batches of up to 10 5 genetically identical sporophyte seedlings can be produced at any time in the laboratory and explanted in the field for production of biomass. Sexual crosses of selected Macrocystis pyrifera gametophyte parents of different geographic origin along the coast of Chile showed heterosis and produced sporophyte batches with superior growth performance. Starting from zygotes, after 10 weeks in the laboratory and 5 months in the sea, our best hybrid genotypes grew up to 11 kg fresh weight per frond, which corresponds to 66 kg m 1 of line in a commercial mariculture installation. In contrast, average yields of 14.4 and 22 kg m 1 are reported in the literature for traditional methods. Additional experiments, including inter-specific crosses M. pyrifera × M. integrifolia and their performance in different climate zones of Chile, confirm that heterosis is a powerful tool for crop improvement in Macrocystis. It opens the possibility to construct tailor-made heterosis genotypes with maximum productivity and/or other desired properties for any given locality.