Functioning Habitat
Beaches and Marine Vegetation
Floating kelp bed area
Vital Sign Indicator
Acre (acres)

No targets are currently set for this indicator.

Danielle Claar
Contributing Partners
Last Updated
5/22/2023 10:00:07 AM
Long-term trends in floating kelp bed area at locations are denoted by points, categorized as: increasing, decreasing, no trend, total loss, no floating kelp, or limited data. The sub-basin status assessment integrates results at locations and other information sources into an overall classification. The time span varies by dataset, with 2021 the most recent year for all datasets.

This indicator assesses long-term trends in the extent of canopy-forming kelp forests at sampling locations throughout Washington State by tracking the area of kelp beds on the water surface. Results at each location are synthesized with other information into an overall assessment of floating kelp status within 11 sub-basins defined by oceanography.

Vital Sign Indicator Chart

The proportion of locations in each long-trend category within each sub-basin. Sub-basins are sorted geographically, from coastal sub-basins (left) to the innermost basin (right). Hood Canal is not included because there are no sampling locations there. This figure visualizes the same location results as the map, in bar chart form. (SCO - Southern Coast; NCO - Northern Coast; WST - Western Strait of Juan de Fuca; EST - Eastern Strait of Juan de Fuca; SJI - San Juan Islands; NPS - North Puget Sound; SWH - Saratoga & Whidbey Basins; ADM - Admiralty Inlet; CPS - Central Puget Sound; SPS - South Puget Sound)

Like terrestrial forests, kelp forests form extensive living structures that provide an array of valuable ecosystem goods and services. These highly productive habitats support diverse species, ranging from small invertebrates to commercially important fish. Additionally, three categories of animals listed under the Endangered Species Act (ESA) depend on kelp habitats: rockfish, salmon, and Southern Resident killer whales.

Kelp has cultural importance to indigenous peoples of the Pacific Northwest. It supports traditional food sources, and plays an important role in art, spirituality, and symbolism.

Concern about kelp losses is widespread, both globally and locally (summarized in Calloway et al., 2020). In recent years, studies have shown that dramatic losses predominate in some areas of Washington State while other areas appear stable. The impacts of declines on the many species that depend on kelp are not understood. In 2020, The Puget Sound Kelp Conservation and Recovery Plan (Kelp Plan) outlined a research and management framework for coordinated action to improve understanding of trends, while also implementing recovery and protection (Calloway et al. 2020).

The floating kelp indicator is produced through a unique partnership of organizations that value kelp. The group has formed an alliance for ongoing work, The Kelp Forest Monitoring Alliance of Washington State (KelpForestsWA). Indicator information is tracked on the Puget Sound Partnership’s Vital Signs website, and is used by Kelp Plan implementers and other organizations.

Key Vital Sign Indicator Results

This is the first report for this indicator, and it was made possible by a unique collaboration among a diverse group of organizations and individuals, including state agencies, Tribes, community science, and NGOs. The results of this indicator will inform kelp management and restoration across Washington State.

  • Along the northern outer coast and Strait of Juan de Fuca, floating kelp populations are stable in the long-term, with high interannual variability. The majority of locations show no long-term trend or increases over decades. One exception is the eastern Strait of Juan de Fuca near Protection Island, where substantial losses have occurred along some shorelines.
  • Declines have been documented in Central and South Puget Sound, with total loss at a number of sites. Over a century time scale and longer, historical ecology studies indicate that floating kelp has disappeared from approximately 80% of the shorelines where it was observed.
  • There is concern that floating kelp has declined in the San Juan Islands, based on indigenous scientific knowledge and other reports. However, data limitations and a short temporal record limit our understanding.
  • Total loss of floating kelp has been observed along some shorelines at the entrance to Possession Sound, which leads to concern about the state of floating kelp in Saratoga and Whidbey sub-basin. However, data gaps prevent sub-basin assessment.
  • In Admiralty Inlet and North Puget Sound, spatial and temporal data gaps preclude assessment. Monitoring results at a limited number of locations did not raise major concerns. 
  • Although approximately one-half to one-third of floating kelp locations in Washington are classified as stable, the impact of multiple stressors such as climate change, heatwaves, nutrient imbalances, and urbanization warrant caution and prompt additional research.
  • The integrated sub-basin status assessment can inform scientific and management priorities for sub-basins. Where floating kelp is stable, conservation is a priority. Where substantial declines are documented, stressor abatement and restoration are priorities. In areas with insufficient data, more monitoring is needed.
Monitoring Program

The floating kelp indicator is produced through a unique alliance of organizations that value kelp, known as The Kelp Forest Monitoring Alliance of Washington State (KelpForestsWA).

Data Source

The Kelp Forest Monitoring Alliance of Washington State (KelpForestsWA)

Samish Indian Nation

Northwest Straits Commission

Washington Department of Natural Resources

The indicator assesses long-term trends in the extent of canopy-forming kelp forests at 171 sampling locations in Washington State. Trends are assessed by tracking changes in the bed area of kelp floating on the water surface through a number of monitoring methods. The general approach is summarized here (see the monitoring protocols for details).

In Washington State, two kelp species form extensive buoyant canopies that float on the water surface, bull kelp (Nereocystis luetkeana) and giant kelp (Macrocystis pyrifera). Bull kelp is widespread, while giant kelp is restricted to the outer coast and the Western Strait of Juan de Fuca.

The floating kelp bed area indicator is distinct from many other Puget Sound Vital Sign indicators because the project team represents a broad-based alliance of organizations and communities that value kelp. A core consideration throughout the development of the floating kelp bed area indicator was to weave together multiple ways of knowing beyond quantitative scientific datasets. Two principles drive this approach. First, diverse engagement helps to ensure that conservation efforts reflect social values (Uffman-Kirsch et al., 2020). Second, projects with widespread engagement are more likely to result in positive conservation outcomes (LeFlore et al., 2021). Data sources include:

  • Samish Indian Nation – classification of aerial imagery and Indigenous Scientific Knowledge.
  • Northwest Straits Commission – volunteer kayak surveys conducted by Marine Resource Committees.
  • The Washington State Department of Natural Resources (DNR) – classification of aerial imagery and kayak surveys.

To meet the identified needs to assess trends in floating kelp, the monitoring project has been phased to quickly provide basic information to managers and scientists while also defining a framework for incremental enhancement over time.

Methods to delineate floating kelp vary slightly among groups within the monitoring alliance. Survey techniques include small boat surveys and aerial imagery collection and classification. Data collection is restricted to summer months when floating kelp forests are at their greatest seasonal extent. To maximize kelp detection, surveys are conducted during periods of low tide, slack currents, and calm weather.

The primary statewide metric is floating kelp bed area. The bed is defined as the area encompassing kelp tissues floating on the water surface and small gaps between adjacent individuals. This metric was selected because it has the most extensive available data, both temporally and spatially. The distance threshold for grouping adjacent individuals into beds varies with individual monitoring protocols, ranging from 8 to 20 m. The program also tracks other parameters at a subset of sites, including canopy area (i.e., the area of floating individuals on the water’s surface, excluding the gaps between individuals). All available parameters are considered during trend assessment.

Long-term trends are reported by location, divided into two categories: ‘sites’ are surveyed by kayak (~1 km) and ‘zones’ are surveyed with aerial imagery (~5-10 km). The size of monitoring locations varies with the extent of shallow subtidal habitat and also with monitoring methods – generally aerial photography captures larger zones (generally 5-10 km of shoreline) while kayaks are deployed at smaller sites (see “Critical Definitions” for location definitions). For the indicator, we assess long-term trends of bed area at each sampling location by integrating information from both kayak surveys at sites and aerial imagery surveys for zones.

Long-term trends are assessed at each location (site and zone) using simple linear regression. Regression analysis is performed over the entire data record available for a given location. Because the indicator is based on synthesis of available data, both the length and timing of data records vary among locations. At least 5 years of floating kelp bed area data (either 5 continuous years or a dataset that spans 5 years) is regressed against year (a p-value < 0.05 suggests a significant trend). Regression outputs are reviewed by an expert and over-ruled (i.e., changed) if the data violates statistical assumptions (e.g., linearity) or if the result fails to consider known kelp dynamics at particular locations or time periods (e.g., total loss). Generally, locations with a significant positive trend are assigned ‘increasing’, significant negative trend assigned ‘declining’, and no significant trend assigned ‘no trend’ (see Table 1 for trend categories). ‘Total loss’ is assigned when a location has previously documented floating kelp beds, but floating kelp was absent from that location in the most recently surveyed year.

Results at monitored locations are synthesized with other information (e.g., historical data, indigenous scientific knowledge, community science) to produce an integrated status assessment within each of 11 sub-basins that comprehensively span Puget Sound and the open coast (see Table 1 for status categories). Ideally, status would be evaluated relative to a defined baseline or target. Since neither a baseline nor a target exist for floating kelp, the status categories weave together information about change over time, condition, and information completeness for each sub-basin. 

Floating kelp status for each sub-basin considers multiple lines of evidence: long-term trend data at locations (described above), Indigenous Scientific Knowledge, historic shoreline extent of kelp based on nautical charts, expert and citizen science observations, agency reports, peer-reviewed scientific literature, and other grey literature. Dataset synthesis considers the magnitude of change, the signal-to-noise ratio, the time scale of the change, and other uncertainties or assumptions.

Critical Definitions

Location: the smallest spatial unit for floating kelp extent trend assessment with two types:

  • Sites - individually identified areas, with a general size of ~1 km of shoreline. Surveyed by kayak.
  • Zones - spanning ~5 – 10 km of shoreline, with boundaries placed at geomorphic features such as headlands. Surveyed using aerial photography. Zones are defined for all shorelines in the southern and northern coast, western and eastern Strait of Juan de Fuca, the San Juan Islands and DNR Aquatic Reserves.

Location trend categories:

  • Increasing – positive (statistically significant) change in area over time
  • No trend – no statistically significant change in area over time
  • Decreasing – negative (statistically significant) change in area over time
  • Total loss – floating kelp was present in the data record but absent in the most recent year
  • Limited data – quantitative data is available but is not sufficient to perform regression or assess long-term changes using alternative methods
  • No floating kelp – all surveys show absence of floating kelp
  • No data – no surveys available

Sub-basin: the largest spatial unit for status assessment, based on large-scale oceanographic features that are associated with environmental conditions. Eleven sub-basins are delineated within Washington’s waters.

Sub-basin status categories:

  • Stable – no long-term change in extent over time.
  • Concern of losses – data sources suggest losses, but quantitative data lack sufficient spatial or temporal detail (low signal-to-noise ratio).
  • Substantial documented decline – data sources demonstrate major losses (high signal-to-noise ratio).
  • Insufficient information – data sources do not provide sufficient spatial or temporal certainty to classify the sub-basin as stable, concern, or decline.
  • No floating kelp – all available data sources show floating kelp has been absent historically and is currently absent.

Indigenous scientific knowledge – Indigenous science is about the knowledge of the environment and knowledge of the ecosystem that Indigenous Peoples have. It is the knowledge of survival since time immemorial and includes multiple systems of knowledge(s) such as the knowledge of plants, the weather, animal behavior and patterns, birds, and water among others. (definition from Indigenous science –

Interpretation of Results

Abundance and Distribution of Floating Kelp in Washington State

Information on broad patterns in floating kelp abundance and distribution could inform science and management actions. However, efforts to estimate abundance are limited by major data gaps, as well as large natural year-to-year variability in floating kelp. (For example, the maximum extent of beds is 3.6 times the minimum extent in areas with multi-decadal monitoring data).

To provide context for science and management, we constructed an order of magnitude estimate of current floating kelp abundance in each sub-basin, based on monitoring data and other inventories (Figure 1). The Western and Eastern Strait of Juan de Fuca each have approximately one-third of the total area of floating kelp beds. The north coast, San Juan Islands, and North Puget Sound contain between 5 and 20%. Admiralty Inlet and Saratoga/Whidbey sub-basins each contain 1 to 5%. Central and South Puget Sound each contain approximately 1% of the total resource. Floating kelp has not been recorded in Hood Canal or along the south coast. The results in Figure 1 constitute our best order-of-magnitude estimate of current distribution. It does not reflect historical distribution or extent, which we expect was greater in many areas. We will refine this preliminary estimate over time with additional data.

Figure 1. The area of nearshore habitat (between -15 m and -1 m depth, Mean Lower Low Water) and percent of total statewide floating kelp bed area by sub-basin. Nearshore habitat area is estimated using diverse bathymetry sources. The floating kelp area estimates represent order of magnitude extrapolations based on existing survey data and expert knowledge (described in the monitoring protocol).


As expected, floating kelp beds are generally more extensive closer to the open ocean, in areas of high current and rocky substrate. However, floating kelp distribution does not track closely with the total amount of nearshore habitat (the area between -15 m and -1 m depth, relative to Mean Lower Low Water). This is because many sub-basins have substantial areas that do not support floating kelp, such as sand flats, which lack hard substrate for floating kelp holdfast attachment.

An interactive map explores results at sampling locations and sub-basins in detail (webmap).


Temporal and Spatial Extent of Floating Kelp Monitoring Data

A total of 171 monitoring locations are included in the indicator dataset. The time span of the data record at locations varies widely (Figure 2). The most extensive temporal record exists along the Strait of Juan de Fuca and open coast, with more than 30 years of annual fixed wing aerial monitoring. Most locations in other regions have 10 years or fewer of data. After integrating all available data sources, four (out of 11) sub-basins did not have sufficient data to complete a definitive status assessment (Admiralty Inlet, North Puget Sound, The San Juan Islands, and Saratoga/Whidbey Basin).

Figure 2. The number of years surveyed and count of monitoring locations (sites or zones) included in the floating kelp indicator. Hood Canal is not included, because floating kelp has not been documented in this sub-basin, nor has repeat surveying been conducted.


The spatial extent of monitoring data varies widely by sub-basin (Table 1). A large proportion of the shoreline within sub-basins along the coast and strait have annual monitoring data. The north coast (NCO), south coast (SCO), and Western and Eastern Strait of Juan de Fuca (WST and EST) have 75-100% coverage. The San Juan Islands (SJI) have comprehensive coverage, but the time span is limited and there are uncertainties due to methodology. In Central Puget Sound (CPS) and South Puget Sound (SPS), monitoring results from a limited number of locations are augmented by extensive long-term studies. In the other sub-basins, a tiny portion of the shoreline has monitoring data. In these areas, assessment was driven by additional data sources (noted in presentation of results).


Table 1. Number of sampling locations and percent of total nearshore habitat (between -15 m and -1 m, MLLW depth) monitored for floating kelp, summarized by sub-basin.
Sub-basin Number of locations monitored Percent of nearshore extent monitored Considerations
Admiralty Inlet (ADM) 2 <1% Sampling locations span low percentage of sub-basin and limited time period.
Central Puget Sound (CPS) 9 2% Sampling locations span low percentage of sub-basin and limited time period. Comprehensive studies have identified floating kelp extent and long-term changes.
Eastern Strait of Juan de Fuca (EST) 37 80% More than 30 years of annual data for majority of sub-basin. Historical study provides century-scale comparison.
Hood Canal (HDC) 0 0% No floating kelp observations known in the sub-basin (south of Lofall).
Northern Coast (NCO) 20 100% More than 30 years of annual data for majority of sub-basin.
North Puget Sound (NPS) 8 3% Sampling locations span extremely low percentage of sub-basin and extremely limited time period.
Southern Coast (SCO) 17 75% No floating kelp observed along the southern portion of open coast. Data absent in embayments, but generally not potential floating kelp habitat.
San Juan Islands (SJI) 47 100% Comprehensive monitoring using aerial photography. However, limited time span in most areas (< 3 years). Strong currents and narrow beds challenge aerial photography methods.
South Puget Sound (SPS) 6 <1% Sampling locations span low percentage of sub-basin and limited time period. Comprehensive studies have identified floating kelp extent and long-term changes.
Saratoga / Whidbey Basin (SWH) 3 2% Sampling locations span extremely low percentage of sub-basin and extremely limited time period.
Western Strait of Juan de Fuca (WST) 23 100% More than 30 years of annual data for majority of sub-basin. Historical study provides century-scale comparison.


Multiple natural and human factors known to impact kelp could be contributing to observed patterns. Floating kelps experience a high degree of natural variability in abundance on inter-annual and decadal scales. This variability is often linked to fluctuations in water temperature via large-scale climate oscillations (Pfister et al. 2018). Other stressors include water turbidity, sedimentation, algal epiphytes, water column nutrients, and grazers (Hollarsmith et al., 2022). Sea urchins are known for their ability to completely denude kelp beds in other regions; however, this phenomenon has not been observed in Washington State. Other grazers, such as kelp crabs (Pugettia producta) and Lacuna spp. snails may exert stronger grazing pressure, especially in areas with moderate waves and currents. Sea star wasting disease (SSWD) may have decreased natural predation levels on some grazers. 

A general pattern has been observed in Washington State: concern about floating kelp losses increases with distance from the coast into Puget Sound. Along this gradient, both natural and human stressors increase. However, causes of floating kelp losses are likely site specific, and vary among locations and sub-basins.

Increasing water temperatures and climate change are major emerging concerns. In many regions within the northeast Pacific, including Washington State, floating kelp populations dropped around 2014 during a marine heat wave. Floating kelp recovery in Washington State was spatially complex. Along the outer coast and Strait of Juan de Fuca, total floating kelp extent rebounded in 2015. In contrast, recovery was delayed until 2017 at Cherry Point in North Puget Sound. At some sites in inner basins, total losses were observed and beds have not recovered (such a Mukilteo in Saratoga Passage and Devils Head in South Puget Sound).

In some areas in recent years, environmental conditions (such as temperature and nutrient concentrations) approached thresholds associated with decreased physiological performance and reproductive success. Long-term data on these parameters is lacking, so it is not known whether they have changed over time.

This is only the first iteration of the statewide assessment of floating kelp, produced with existing data in order to address pressing needs for greater understanding of status and trends. We believe that the assessment reliably identifies broad patterns in floating kelp abundance and distribution. It also creates a model for integrating diverse information sources in a holistic approach to synthesize floating kelp data. Future monitoring will be devoted to further developing our understanding and linking findings to research, restoration, and conservation actions. Where floating kelp is stable, conservation is a priority. Where substantial declines are documented, stressor abatement and restoration are priorities. In areas with insufficient data, more monitoring is needed

The Project Team identified priorities for enhancement of the monitoring program (discussed in the monitoring program design report). Future enhancements will require additional funding; highlights include:

Fill gaps in ongoing monitoring through expanding existing programs and incorporating other external datasets, especially in sub-basins identified to have limited data in the status assessment.

Implement methodological improvements and expand kelp parameters and metrics through upgrading monitoring methods to incorporate new technology. Also, describe a greater range of kelp parameters and metrics. Proposed expansions could be tested first at a subset of sites.

Determine resources available for annual monitoring and identify core annual monitoring areas. If comprehensive annual monitoring is not feasible, the study area will need to be sub-divided into core areas surveyed annually and other areas surveyed less frequently, as is done by the DNR Submerged Vegetation Monitoring Program.  

Integrate existing historical datasets to increase the time span of the monitoring record. Expanding the temporal baseline will increase understanding of changes over time. The sub-basin status assessment identifies major data gaps.

Enhance geographic assessment area delineation. Complete and refine zone delineations, prioritizing areas with new incoming data. Refine the hierarchical system over time.

Explore linkages to environmental data. Physical and biological datasets will help to inform interpretation of monitoring results, i.e. declines or increases of floating kelp area. Consider testing synthesis of existing data and new data collection at a subset of sites.

WA Floating Kelp Indicator Project website

Interactive webmap

Statewide summary report

Monitoring program design and data assessment protocols report


Partner websites:

Samish Indian Nation

Northwest Straits Commission

Washington Department of Natural Resources



Calloway M, Oster D, Berry H, Mumford T, Naar N, Peabody B, Hart L, Tonnes D, Copps S, Selleck J, Allen B, Toft J (2020) Puget Sound kelp conservation and recovery plan. Prepared for NOAA-NMFS, Seattle, WA. 52 pages plus appendices. Available at:

Hollarsmith JA, Andrews K, Naar N, Starko S, Calloway M, Obaza A, Buckner E, Tonnes D, Selleck J, Therriault TW (2022) Toward a conceptual framework for managing and conserving marine habitats: A case study of kelp forests in the Salish Sea. Ecology and Evolution 12(1):e8510.

LeFlore M, Bunn D, Sebastian P, Gaydos JK (2021) Improving the probability that small-scale science will benefit conservation. Conservation Science and Practice 4(1): e571.

Pfister CA, Berry HD, Mumford T. The dynamics of kelp forests in the Northeast Pacific Ocean and the relationship with environmental drivers (2018) Journal of Ecology 106(4):1520-33.

Uffman-Kirsch LB, Richardson BJ, van Putten EI (2020) A new paradigm for social license as a path to marine sustainability. Frontiers in Marine Science 7: 1–6.


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