Introduction

Earth is currently experiencing rapid changes in climate, associated with anthropogenic activities, which have the potential to have significant effects on aquatic ecosystems. The 9th International Workshop of the Group for Aquatic Primary Productivity (GAP9) assessed the effects of environmental factors on physiological performance and primary productivity of micro- and macroalgae. This Introduction summarizes the activities and main findings of the 4 workgroups of GAP9 as published in this Theme Section of Aquatic Biology.