A Long-term Phytoplankton Monitoring Program for Central Puget Sound using Particle Imaging

Puget Sound is a large and highly productive estuarine system that is vulnerable to climate change and anthropogenic impacts from a growing population. King County operates an exceptionally comprehensive, long-running monitoring program designed to assess water quality in the Puget Sound Central Basin. Data are collected year-round for a suite of physical, chemical, and biological parameters. Phyoplankton monitoring using traditional methods was added to the program in 2008 to address a significant biological data gap at the lower trophic level. Since acquisition of a FlowCAM particle imaging system in 2014 the program is generating a more extensive and robust dataset for Puget Sound phytoplankton. This data is critical to assess how changes from climate and other stressors linked to anthropogenic activity may impact Puget Sound’s biodiversity and trophic structure. Twice-monthly samples from eight Central Basin locations are analyzed year round by FlowCAM. Fifty-nine taxonomic categories are characterized using relevant descriptors of assemblage composition, such as particle size (5–300 µm), abundance, and biovolume. Our dataset also includes zooplankton composition and abundance at select stations. Data analysis has focused on environmental parameters (temperature, salinity, nutrients) and weather/climate patterns as drivers of phytoplankton community composition, with special attention to the occurrence of potentially harmful taxa. Besides evident seasonal cycles, multivariate data analysis has revealed distinct geographic clusters among stations and characteristic taxa assemblages that help interpret the dynamics of Puget Sound algal blooms in relation to environmental and biological drivers