Understanding macroalgal dynamics for informed decision-making in the restoration of a Mexican Caribbean reef

Introduction: Caribbean coral reefs have undergone long-term shifts toward macroalgal dominance, potentially constraining coral recovery and restoration outcomes. At Wave of Change (WOC) Reef, an active restoration site in the Mexican Caribbean, previous monitoring has documented high macroalgal cover, yet its intra-annual dynamics and environmental drivers remain poorly understood. Objectives: To (1) determine whether macroalgal cover follows a recognizable intra-annual pattern or responds primarily to episodic events; (2) evaluate whether the functional composition of the benthic algal assemblage, described in terms of growth forms, remains stable or shifts over time; and (3) identify the environmental drivers that best explain macroalgal variability. Methods: Fortnightly photographic benthic surveys were conducted from August 2024 to August 2025 along seven permanent 10-m transects, with 70 photoquadrats (1 m²) collected per sampling event. High-resolution photoquadrats were analyzed using the ReefCloud AI platform. Environmental variables included in situ temperature and underwater illuminance obtained from HOBO loggers, while additional environmental data (Secchi disk transparency, PAR, chlorophyll a, salinity, nitrate, phosphate, and pH) were obtained from the SIMAR database. Temporal patterns and relationships were assessed using non-parametric analyses, redundancy analysis, and beta regression models. Results: Upright macroalgae and algal turfs showed marked temporal variability and alternated in dominance, whereas crustose coralline algae remained consistently low. Dictyota and Halimeda dominated the upright macroalgal assemblage, representing 41.26 % and 22.78 % of its relative composition, respectively. Nitrate was the only significant environmental predictor of benthic algal composition, explaining 21.6 % of the variance and showing contrasting associations with upright macroalgae (negative) and algal turfs (positive). Conclusions: High-resolution benthic monitoring provides an ecological context for interpreting coral restoration trajectories beyond coral performance alone. Integrating AI-assisted benthic assessments into restoration programs can strengthen long-term evaluation and adaptive management at WOC Reef and other restoration sites in the Mexican Caribbean.