Halogen and oxyanion variability in marine algae: A study in the St. Martin’s Island, Bangladesh

Halogens and oxyanions play essential roles in marine biogeochemical cycles, yet studies on their distribution in algae remain extremely limited. This work provides the first baseline profile of these ions in the macro- and microalgae of St. Martin’s Island, Bangladesh. Eight species representing Chlorophyta, Phaeophyta, Rhodophyta, and Cyanophyta were collected during the post-monsoon period, when algal abundance is highest. Anion measurements were carried out using Ion chromatography. Chloride and sulfate were consistently present across all species, with chloride ranging from 3.83 mg · g⁻¹ to 23.94 mg · g⁻¹ and reaching its highest level in Ceramium fastigiatum, while sulfate ranged from 2.88 mg · g⁻¹ to 21.35 mg · g⁻¹ and peaked in Padina tenuis. Fluoride was generally below detection except in Lyngbya confervoides (0.10 mg · g⁻¹) and two red macroalgae, including Hypnea boergesenii (3.83 mg · g⁻¹). Nitrate accumulation varied among species, with L. confervoides showing the lowest level (0.06 mg · g⁻¹) and Cladophora echinus the highest (0.32 mg · g⁻¹). As an exploratory dataset, the study documents only the post-monsoon ion patterns and does not capture seasonal or fine-scale spatial variability. Even within this scope, the findings fill a critical regional gap and offer an initial biochemical reference for future ecological assessments and environmental monitoring programs around St. Martin’s Island.