Environmental context. The present study examines arsenic species in kelp and associated grazing animals of an Ecklonia radiata food chain. The study focusses on the changes in proportions of arsenoribosides obtained from E. radiata and mechanisms are proposed to explain the transformations of arsenoribosides observed in the organisms that graze on it.

Abstract. Total arsenic and arsenic species in the tissues of three growth stages of the macroalgae Ecklonia radiata and within organisms that feed on it are reported. Arsenic concentrations in E. radiata tissues varied from 40 to 153 μg g^–1. Growth stage did not influence arsenic concentrations or arsenic species. E. radiata contained glycerol arsenoriboside (1–8.5%), phosphate arsenoriboside (10–22%) and sulfonate arsenoriboside (73–91%). Arsenic concentrations varied significantly among animal species and between tissues (5–123 μg g^–1). Animals contained variable quantities of arsenobetaine (14–83%). Haliotis rubra tissues contained high concentrations of glycerol trimethylarsonioriboside (0.7–22%) and the fish Odax cyanomelas contained large quantities of phosphate arsenoriboside (25–64%) with little arsenobetaine (1.5–15%).

Arsenoribosides consumed from macroalgae are substantially converted or differentially accumulated as glycerol and phosphate arsenoribosides in animal tissues. In all animals, phosphate arsenoriboside would appear to be conserved or synthesised de novo. In gastropods, glycerol trimethylarsonioriboside and thio arsenic species are formed in the digestive system. Thus, the intermediate arsenic species that form a plausible pathway for the formation of arsenobetaine from dimethylarsenoribosides are present.