The perceived increase in global harmful algal blooms (HABs) is investigated using data from the Harmful Algae Event Database (HAEDAT) and Ocean Biodiversity Information System (OBIS) from 1985-2018. The study finds no uniform global trend in HAB frequency and distribution after adjusting for regional monitoring effort variations. Regional trends varied due to differences in bloom species, type, and impacts. Intensified monitoring, linked to aquaculture expansion, is suggested as the primary reason for the perceived increase, highlighting the need for regionally and species-specific trend analyses.

Gustaaf M. Hallegraeff, Donald M. Anderson, Catherine Belin, Marie-Yasmine Dechraoui Bottein, Eileen Bresnan, Mireille Chinain, Henrik Enevoldsen, Mitsunori Iwataki, Bengt Karlson, Cynthia H. McKenzie, Inés Sunesen, Grant C. Pitcher, Pieter Provoost, Anthony Richardson, Laura Schweibold, Patricia A. Tester, Vera L. Trainer, Aletta T. Yñiguez, Adriana Zingone