The West Antarctic Peninsula (WAP) is a climatically-sensitive region where periods of strong warming have caused significant changes in marine ecosystem and food web processes. Tight coupling between phytoplankton and higher trophic levels implies that the coastal WAP is a bottom-up controlled system, where changes in phytoplankton dynamics may largely impact other food web components. Here, we analyzed the interdecadal time series of year-round chlorophyll-a (Chl) collected from three stations along the coastal WAP, Carlini Station at Potter Cove (PC) on King George Island, Palmer Station on Anvers Island, and Rothera Station on Adelaide Island. There were trends toward increased phytoplankton biomass at Carlini Station (PC) and Palmer Station, while phytoplankton biomass declined significantly at Rothera Station over the studied period. The impacts of two relevant climate modes to the WAP, the El Niño-Southern Oscillation and the Southern Annular Mode, on winter and spring phytoplankton biomass appear to be different among three sampling stations, suggesting a possibly more important role of local-scale forcing than large-scale forcing on phytoplankton dynamics at each station. The interannual variability of seasonal bloom progression derived from considering all three stations together captured ecologically meaningful, seasonally co-occurring bloom patterns which were primarily constrained by water-column stability strength. Our findings highlight a coupled link between phytoplankton and physical and climate dynamics along the coastal WAP, understanding of which is crucial in predicting overall WAP food web responses to climate change and variability.