To investigate the release and degradation of arsenolipids present in the marine brown macroalga Ecklonia radiata, tissues were collected in various stages of decomposition from intertidal environments, while tissues were also decomposed in laboratory-based microcosms prepared using combinations of autoclaved and natural (non-autoclaved) seawater and sand. Field collected macroalgae samples contained 20–120 μg g−1 total As of which 1–10% were arsenolipids comprising mainly an arsenic hydrocarbon (AsHC; 3–13% of total arsenolipids) and four di-acyl arsenic phospholipids (AsPLs; 86–95%). Additionally, a mono-acyl AsPL was found in all water-column decomposing samples. Arsenolipid concentrations in live tissues were similar to those in tissues decomposing in the water-column (1.3–2.9 μg g−1 dry mass), which were both up to four times higher than those in decomposing tissues collected from intertidal environments (0.7–1.3 μg g−1 dry mass). In the microcosm experiments, the arsenolipid content of E. radiata decreased substantially as decomposition proceeded. In the majority of microcosms, more than 75% of the arsenolipids present initially disappeared within 5 days with only the AsHC persisting until day 60 (the length of the experiment). This study demonstrates that the habitat in which decomposition occurs influences the release and degradation of arsenolipids with the greatest losses occurring when tissues decompose in intertidal environments. Microbial diversity, biomass, and overall activity are thus likely to play important roles in the persistence of arsenolipids in decomposing algae.