Zooplankton are small organisms that are generally carried with the flow of water currents. The diversity within this group in Puget Sound marine waters encompasses copepods, euphausiids (krill), cnidarians and ctenophores (jellies), amphipods, larval stages of benthic invertebrates such as crabs and oysters, larval fish, and more. These diverse taxa play a variety of unique roles in the marine ecosystem. Zooplankton are consumers of tiny plant-like organisms (phytoplankton) that form the base of the marine food web, as well as other zooplankton. In turn, zooplankton (particularly the larger species), are important prey for juvenile salmon and small forage fish.

Due to their diversity and key position in the marine food web, zooplankton communities reflect the integration of many ecosystem characteristics over seasonal and annual timescales. These ecosystem characteristics include oceanographic and estuarine circulation, phytoplankton community composition and productivity, physical and chemical conditions, and predation. For these reasons, the zooplankton community composition data collected for this program are a valuable measure of biological response to environmental change.

King County’s zooplankton monitoring program, which began in 2014, is a collaboration with Dr. Julie Keister at the University of Washington (UW) and contributes data to the Salish Sea Marine Survival Project (SSMSP) headed by Long Live the Kings. King County collects zooplankton samples at four locations in Puget Sound twice monthly February-November and once monthly December-January. Samples for phytoplankton as well as water quality parameters such as salinity, nutrients, chlorophyll, and dissolved oxygen are collected at the same time as zooplankton samples.

King County samples for zooplankton using two types of nets, which each capture different components of the zooplankton community. To capture smaller zooplankton such as copepods, which typically dominate zooplankton biomass, a fine-mesh (200 micrometers, μm) ring net is deployed to a maximum depth of 200 meters (m) and then raised to sample the entire water column. To capture larger zooplankton, which may swim fast enough to escape the slower vertically-towed net, a double “bongo” net with larger mesh (335 μm) is towed obliquely (at an angle) down to a depth of 30 m and then back to the surface.

Samples undergo detailed analysis by expert taxonomists in Dr. Julie Keister’s laboratory at UW. Zooplankton are identified to species and life-cycle stage where possible and are measured for biomass estimates.

View a copy King County’s zooplankton monitoring program sampling and analysis plan.

Data from the zooplankton monitoring program are available here. Please contact MarineWQ@kingcounty.gov with any questions about the program.