Influence of environmental seasonality and marine pollution on the phenology of the kelp Lessonia spicata (Phaeophyceae)

This study examines the phenological response of Lessonia spicata to environmental variability and anthropogenic stress. Two central Chilean sites with contrasting pollution levels were selected: Horcón (high impact) and Quintay (low impact). Sori were collected in spring 2023 and autumn 2024 to assess reproductive effort, followed by a 28-day culture period. Weekly observations recorded spore settlement, germination, sex ratio, fecundity, reproductive success, and sporophyte density. The results indicate that the reproductive effort reached a maximum in autumn at both sites (> 50%), with season having a significant effect; the lowest values were recorded in Quintay during spring (< 30%). Early development varied by site and season, with sustained growth in Quintay cultures and early gametophyte loss in the Horcón autumn cultures. Sex ratio varied significantly between sites but not seasons. By day 21, Horcón autumn cultures showed complete loss of gametophytes, while Quintay maintained a stable ~ 50% ratio. Fecundity also displayed a significant site-season interaction, showing a maximum in Horcón during autumn (> 90%). Sporophyte formation followed the same tendency, reaching 100% in Horcón by days 21 and 28. This apparent success likely resulted from early bleaching that eliminated most gametophytes, allowing only viable individuals to be fertilized, potentially inflating success estimates. Sporophyte density was significantly lower in autumn, especially in Horcón where necrosis and degradation were evident. Our results suggest that anthropogenic contamination affects L. spicata phenology and may compromise long-term persistence. Pollution, in combination with seasonal dynamics and environmental drivers, such as temperature and nutrient variability, could potentially influence the timing and success of key life cycle stages.