Ecosystem-based management is one of the strategies to protect the coastal areas. One of the key elements is phytoplankton community composition since it represents a good indicator of anthropogenic pressures. This identifies the seasonal patterns of phytoplankton, and its alterations by the stress factors induced by human activities are highly valuable. This research represents the first attempt to study that 476 km of western Mediterranean coastal belongs to the Valencian Community (Spain) based on the phytoplankton composition approach. The water samples during a 5-year period (6757 water samples) were taken to determine its phytoplankton group's dynamics and its relationship with anthropogenic stressors by means of a series of plots and statistical analyses. Diatoms are the group that most contribute to the whole community composition with two periods of maximum abundance. The Prasinophyceae and Cryptophyceae show unimodal patterns varying its maximum values depending on the season. The picocyanobacteria group exhibited the clearest and best-defined pattern. Other groups have no clear seasonal pattern and become abundant in areas of higher anthropogenic pressure. Graphical abstract Figure A contains poor quality of text in image. Otherwise, please provide replacement figure file.A new graphical abstract, with higher quality is attached.