Fisheries Resources Institute 1 article published in JoVE Environment A Standardized Procedure for Monitoring Harmful Algal Blooms in Chile by Metabarcoding Analysis Kyoko Yarimizu1, So Fujiyoshi1, Mikihiko Kawai2, Jacquelinne J. Acuña3, Joaquin-Ignacio Rilling3, Marco Campos3, Jonnathan Vilugrón4, Henry Cameron5, Karen Vergara6, Gonzalo Gajardo6, Oscar Espinoza-González4, Leonardo Guzmán4, Satoshi Nagai7, Carlos Riquelme5, Milko A. Jorquera3, Fumito Maruyama1 1Office of Research and Academia-Government-Community Collaboration, Hiroshima University, 2Graduate School of Human and Environmental Studies, Kyoto University, 3Scientific and Biotechnological Bioresource Nucleus, Universidad de La Frontera, 4Centro de Estudios de Algas Nocivas, Instituto de Fomento Pesquero, 5Ciencias del Mar y Recursos Biologicos, Universidad de Antofagasta, 6Departamento de Ciencias Biológicas y Biodiversidad, Universidad de Los Lagos, 7Japan Fisheries Research and Education Agency, Fisheries Resources Institute This protocol introduces steps of metabarcoding analysis, targeting 16S rRNA and 18S rRNA genes, for monitoring harmful algal blooms and their associated microbiome in seawater samples. It is a powerful molecular-based tool but requires several procedures, which are visually explained here step-by-step.