ALGINATE COMPOSITION OF LESSONIA-TRABECULATA (PHAEOPHYTA, LAMINARIALES) GROWING IN EXPOSED AND SHELTERED HABITATS

Lessonia trabeculata forms extensive kelp beds in Chilean subtidal environments. It commonly occurs in wave exposed habitats, and occasionally in sheltered habitats. Different hydrodynamic regimes produce morphologically and physiologically distinct plants. This study investigated alginate composition in Lessonia trabeculata growing in two habitats which differed in intensity of water movement. Blades of sporophytes at an exposed beach (El Frances) were significantly narrower and thicker (P < 0.05) than those from a protected bay (La Herradura). Alginates from blades at the exposed site showed a significantly lower M/G ratio (P < 0.05) and a higher percentage of guluronic blocks than those from the protected site. Stipes and holdfasts showed insignificant differences in M/G ratio and in block composition between the two sites. A transplant experiment showed that the blades of sporophytes from El Frances transplanted to La Herradura Bay were significantly higher in M/G ratio and content of MM blocks. In sporophytes transplanted from La Herradura to El Frances the M/G ratio decreased significantly (P < 0.05) and showed an increase in content of GG blocks. Differences in M/G ratio and block composition between populations of Lessonia trabeculata appear to arise as an adaptative response to hydrodynamic activity of the habitat, realized through modifications in alginic acid biosynthesis.