First estimates of productivity in Lessonia trabeculata and Lessonia nigrescens (Phaeophyceae, Laminariales) from the southeast Pacific

Lessonia is the main Laminariales found along the southeast Pacific coast. Lessonia nigrescens Bory de Saint‐Vincent in the intertidal and Lessonia trabeculata Villouta et Santelices in the subtidal, are the most important habitat constructors in rocky coastal communities in northern and central Chile. In both species, the seasonal production and erosion of distal tissue were estimated in biomass units using the Area of Constant Biomass Model that combined the individual blade elongation, obtained with the traditional hole‐punching method, with the blade length and biomass distribution along the blade. In austral late spring (December 96) and autumn (May 97), blade production and erosion were transformed to the level of population from standing stock measurements (number and biomass of blades and plants per substrate area), considering that previous blade weight analysis showed the highest and lowest values at these times, as well as the population parameter extremes that were expected to occur. Both species displayed a seasonal pattern, with a production increase in later winter and spring and decrease towards the end of summer that coincided with higher distal tissue erosion. At the level of individual blades, Lessonia trabeculata showed higher mean production (0.026 g dw d^?1) and erosion (0.01 g dw d^?1) than L. nigrescens (production 0.01 g dw d^?1 and loss 0.002 g dw d^?1). The standing stocks, with respect to density and biomass, were similar in spring and autumn for both populations. Nevertheless, the net productivity (production minus erosion) of the intertidal L. nigrescens showed greater values due to the greater density of blades (2112 ± 1360 (SE) blades m^?2) compared with the subtidal L. trabeculata (527 ± 151 (SE) blades m^?2). Spring net productivities of 42 g dw m^?2d^?1 (254 g ww m^?2d^?1; 11.46 gC m^?2d^?1) for L. nigrescens and 11 g dw m^?2 d^?1 (64 g ww m^?2 d^?1; 2.46 gC m^?2d^?1) for L. trabeculata were estimated. A preliminary model of production and biomass fate for Lessonia populations is proposed.