Anoxia is regularly listed as a major consequence of harmful algal blooms (HABs), in the form of high biomass blooms often referred to as red tides. However, the linkage of these blooms to anoxia and consequent mortalities within ecosystems is poorly documented and in many cases anecdotal. Their local and transient character is likely to have contributed to our poor understanding of these events. Objectives: • Define HAB related hypoxia/anoxia [as opposed to other low oxygen phenomena in coastal waters]. • Assess the scale of the problem [incidence/frequency/distribution/impact] of low oxygen events attributed to HABs [and identified trends]. Also assess the impacts on marine life of low oxygen versus HAB derived toxins. • Identify drivers of HAB related hypoxia/anoxia [susceptible marine systems, dominant species, role of eutrophication and climate change]. • Identify processes that mediate bloom-to-post-bloom transitions important in determining the biogeochemical fate of the bloom and the consequent onset of hypoxia/anoxia. • Investigate models [and model requirements] to better understand and predict HAB related hypoxia/anoxia.