Thriving Species and Food Web
Zooplankton Index
Vital Sign Indicator
Index Value (index value)

No targets are currently set for this indicator.

Julie Keister
Contributing Partners
Last Updated
5/10/2023 5:51:03 PM
Map of the Puget Sound Zooplankton Monitoring Program zooplankton stations grouped by Northern Washington (NWA – gold circles) and Puget Sound (PS – purple triangles).

The Zooplankton Index is a concise way to visualize the variability in biomass for select taxonomic groups in Northern Washington and Puget Sound regions. This indicator shows the change in annual average biomass of each zooplankton group, calculated from z-scores. Z-scores depict how far the biomass differs from the annual mean. Values closer to zero are near average, while values farther from zero show a greater difference from the average in any particular year. While these values do not indicate “good” or “bad” outcomes for zooplankton, they are useful in determining how these communities change over spatio-temporal scales.

Vital Sign Indicator Chart

Zooplankton Index reports as z-scores from 2014-2022 for various taxa groups at two regions, Northern Washington (NWA) and Puget Sound (PS). Colors indicate whether the annual average biomass is 1-3 standard deviations (SD) above (positive) or below (negative) the mean. Values are relative within the calculated means of each region and taxon.

The Zooplankton Index is a concise way to visualize the variability in biomass for select taxonomic groups in Northern Washington and Puget Sound regions. While these values do not indicate “good” or “bad” outcomes for zooplankton, they are useful in determining the degree of change these communities encounter over spatio-temporal scales.

Key Vital Sign Indicator Results
  • In Northern Washington waters, total zooplankton biomass (all zooplankton) was well above average in 2015 and 2019, and moderately below average in 2017 and 2021.
  • In Puget Sound, total biomass was also very high in 2015, but remained above average through 2017, and was only moderately high in 2019. Conversely, 2020 and 2021 were low biomass years in Puget Sound with 2018 and 2022 being unremarkable.
  • Small crustaceans generally showed the same pattern as total biomass. 
  • Large crustaceans were markedly higher than the annual mean in 2015 in both regions and were otherwise above the mean only in 2014.
  • Gelatinous zooplankton biomass was highest in 2014 for both regions, yet dramatically declined during and after the 2015-2016 Pacific marine heatwave. While gelatinous zooplankton (consisting here of jellyfish and comb jellies) have long been touted as harbingers of poor ecosystem health, they are proving to be important in diets of pink and chum salmon.
  • Most taxa were more variable across years in Northern Washington than in Puget Sound.
Monitoring Program

Puget Sound Zooplankton Monitoring Program

Data Source

Puget Sound Zooplankton Monitoring Program Dataset

The Puget Sound Zooplankton Monitoring Program (started as the Salish Sea Marine Survival Project from 2014-2020) provides an extensive, ongoing dataset documenting metrics of zooplankton from 15 stations in the southern Salish Sea throughout Northern Washington (NWA) and Puget Sound (PS) (see map above). The data reported in the three Zooplankton Vital Sign indicators are compiled from 200-µm mesh vertical net tows, which are collected bi-weekly year-round, with lower frequency (monthly) in the winter. The nets are towed through the full water column, from within 5 m from the bottom, or to a maximum of 200 m, to the surface. Samples are preserved in 5% formalin and are processed by expert taxonomists at the University of Washington, with certain taxa identified to species level. Data are then statistically analyzed to develop indicators of environmental variability.

Critical Definitions

Taxa of interest

All Zooplankton (total zooplankton biomass) includes all taxa collected, except for Noctiluca (dinoflagellates), eggs, copepod nauplii, and any unidentifiable organisms, as these are extremely small and inconsistently caught in the nets or damaged beyond recognition.

Crustaceans compose the majority of zooplankton biomass in the Salish Sea. This broad taxonomic group consists of several major taxa (copepods, amphipods, krill, shrimp, crabs, etc.), and is separated into size classes (large crustaceans >2.5 mm and small crustaceans <2.5 mm) relevant to forage fish and juvenile salmon diets, including Chinook and coho salmon.

Gelatinous zooplankton consist of cnidarians (e.g., jellyfish) and ctenophores (e.g., comb jellies). These soft invertebrates may have indirect, yet important, linkages to water quality and ecosystem health, and are important prey for pink and chum salmon.

Crab larvae are of high interest in fisheries management, especially several Cancridae species, including Dungeness crab (Metacarcinus magister).

Interpretation of Results
  • There is a caution against making assumptions on the overall welfare of the community simply through this indicator, as a ratio cannot capture synchronous changes (e.g., increases in both highly nutritious crustacean vs gelatinous zooplankton, lower zooplankton values due to grazing or an amplified food web, etc.).
  • Targets have not yet been defined for these indicators. When evaluating trends in the indicators, it is important to note that high biomass of any group would indicate high prey availability for their predators. However, because there is a complex food web in the Salish Sea where sustained predation will decrease biomass, low biomass does not necessarily indicate that the system is in an unhealthier state than when biomass is high.

No datasets uploaded.

Reporting Guidance
Reporting Instructions

No Subcategories for this Puget Sound Indicator.