Abstract

The brown macroalga Lessonia berteroana, a foundation species in northern Chilean kelp forests, may be exposed to hypersaline conditions associated with desalination brine discharges in the absence of biologically based regulatory thresholds, for which no national regulations currently exist. This study assessed under controlled laboratory conditions, the sensitivity of early life stages of kelp L. berteroana to a hypersalinity stress (34-61 practical salinity units, PSU) up to 96 h of exposure through multiple physiological and reproductive endpoints: spore release, photosynthetic performance (F-v/F-m, rETR(max), alpha, E-k), pigment content, and ROS accumulation. The EC50 was estimated for Chl-a (38.7 PSU), Chl-c (40.9 PSU), spore release (42.1 PSU), ROS production (47.9 PSU), and rETR(max) (59.6 PSU). Three response zones were identified: (i) tolerance up to 37.6 PSU, with stable photosynthetic efficiency and reproduction; (ii) a sub-lethal zone (41.1-47.9 PSU), characterized by a pigment decline, reduced spore release, and moderate ROS accumulation; and (iii) severe stress >54.7 PSU, marked by pigment degradation, photoinhibition, exponential ROS production, and reproductive collapse. These findings provide biologically grounded evidence identifying a preliminary ecotoxicological response range for early stages of L. berteroana, providing critical evidence to guide the evaluation and regulation of brine discharge impacts and support the conservation of this species in northern Chilean coastal ecosystems, where this species plays a foundational role in sustaining biodiversity and ecosystem services.