Phytoplankton are a group of microscopic organisms consisting of single-celled or colonial algae. They form the base of marine food webs as the dominant photosynthetic producers (similar to plants on land) and influence water chemistry and nutrient dynamics. Major groups of phytoplankton in marine waters include diatoms, dinoflagellates, and nanoflagellates. Diatoms are relatively large and are adapted to high-nutrient environments. They can multiply rapidly at certain times of the year, such as in early spring in Puget Sound. Diatoms are a major food source for a wide variety of zooplankton, including larger species that are important prey for fish. Dinoflagellates and nanoflagellates, in contrast, generally flourish under lower nutrient conditions and are generally too small to be a good food source for the larger zooplankton. The progression from diatom-dominated communities in the spring to more diverse communities of smaller, motile (flagellated) types of phytoplankton in the summer is a general pattern that is frequently observed in coastal marine waters.

The diversity in responses to environmental conditions and unique roles played by different types of phytoplankton mean that the composition of the phytoplankton community, not just how much phytoplankton is growing, is key information for understanding marine food webs. King County’s phytoplankton monitoring program aims to collect such community composition data throughout the year in the Central Basin of Puget Sound, alongside the commonly measured metric of phytoplankton growth, chlorophyll.

King County’s phytoplankton monitoring program began in 2008 with a semi-quantitative microscopy method of analysis, which assessed the relative abundance of different types of phytoplankton. In 2014, sample analysis with a particle imaging analyzer (FlowCAM^®) was added to the program. This method partially automates identification and quantifies both abundance and size of all phytoplankton present in a sample. The semi-quantitative method was retired at the end of 2014 and superseded by qualitative microscopy. This method provides higher resolution identification to complement the FlowCAM’s quantitative method. For a history of the sampling program view the following table.

King County collects phytoplankton samples offshore at eight sites in Puget Sound, twice monthly from Feb-Nov and once monthly from Dec-Jan. These locations are also sampled for water quality parameters such as salinity, temperature, nutrients, chlorophyll, and dissolved oxygen, as well as zooplankton at three sites (see summary here).

Data from the phytoplankton monitoring program are available here. Please contact MarineWQ@kingcounty.gov with any questions about the program. Phytoplankton images are available here, and publications and presentations are available here.