Several species of harmful algal blooms cause mass mortalities of shellfish in aquaculture farms, including cosmopolitan ichthyotoxic dinoflagellates and raphidophytes. Others are responsible for the contamination of shellfish, notably bivalves with potent toxins that are detrimental to human health, following ingestion. In the latter case, bivalve fishery beds and aquaculture farms remain closed to harvesting for sustained periods of time, lasting months at a time, leading to serious economic losses. Here, the decadal occurrence as well as the impacts of HAB in terms of shellfish mortalities and contamination have been analysed for the Asia-Pacific region, from the period of 1980-2020, for the most recurrent HAB species. The analysed data was driven of the IOC-UNESCO global database, HAEDAT, to identify the most recurrent HAB species and the most impacted bivalve species and geographical regions. GIS was used to represent the decadal geographical distribution of the HAB events and associated effects on bivalve aquaculture.