Key Questions and Recent Research Advances on Harmful Algal Blooms in Stratified Systems

This chapter synthesizes progress achieved in the understanding of the dynamics of harmful algal blooms (HABs) under the auspices of the GEOHAB Core Research Project HABs in Stratified Systems. A variety of aquatic environments are considered, where small-scale hydrographic features may be encountered in stratified water columns. A special emphasis is put on subsurface thin-layer structures, which, thanks to advances in fine-resolution sampling and observation methods, have dramatically changed our comprehension of HAB events. The importance of small-scale physical–biological interactions as well as chemically driven relationships between HAB species and components of the food web are also key topics addressed. Research priorities are identified and the potential offered by new approaches and advanced instrumentation is discussed.