This dataset includes sea star abundance data collected as part of the study described below. See the "Related Datasets" section for size structure data. Mass mortality from disease epidemics can challenge the resistance and resilience of populations and communities. Assessing the impacts of such events and their consequences is crucially dependent on long-term datasets In 2013-16, sea star wasting disease (SSWD) caused population-wide crashes of the archetypal keystone species, the sea star Pisaster ochraceus, along the North American west coast. We used two long-term datasets to assess the resilience of Pisaster populations to this perturbation in Oregon: a 16-year time series (2007-2023) of annual predation rate at 7 sites, and a 23-year time series (2001-2024) of density and size of Pisaster at 8 sites. In spring 2015, a novel and massive Pisaster recruitment event occurred at all sites, averaging 3.00 ± 0.57 recruits m-2 (± SE), an 8,100% increase compared to pre-SSWD. Elevated but spatiotemporally variable recruitment has persisted over the subsequent decade. Before SSWD, population size structure was relatively stable, consisting mostly of large adults with virtually no recruitment. After the outbreak, density, average size, and biomass density declined at nearly all sites, while SSWD persisted at low levels, averaging ~4% symptomatic per year. As of the current period (2021-2024), density and biomass density had recovered at all sites and often overshot prior levels, but average body size recovered at only 3 of 7 sites. However, the 2014 crash and the post-2014 recruitment events apparently destabilized the populations; density remains more variable among years at all but two sites. 

Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Data Files
• Supplemental Files
• Related Publications
• Related Datasets
• Parameters
• Project Information
• Program Information
• Funding

This time series was funded in conjunction with the Long Term Research in Environmental Biology [LTREB] program including the LTREB project listed on this page (Award DEB-2050017) and prior awards (Award DEB-1050694,DEB-1554702).

SSWD = Sea star wasting disease

Our studies took place at eight sites along the Oregon coast spanning ~260 km from 44.5N to 42.75N latitude (Fig. 1, Table S1 of Gravem and Menge (2025)). All are predominantly rocky shores with relatively gentle slopes and have typical patterns of zonation, with a high-intertidal zone dominated by barnacles and fucoid algae, a mid-intertidal zone dominated by mussels, and a low-intertidal zone with a diverse assemblage of macrophytes and sessile invertebrates.

Belt Transects

Because of the importance of Pisaster in influencing community structure through its consumption of mussels and other prey, in 2000-2001 we initiated a program of ~twice-annual belt transects to quantify sea star size structure and density at each site. Surveys generally occurred in spring (April or May) and summer (July, August, or September), but in some years surveys were more or less frequent. Belt transects were replicated (n = 5) in 2 x 5 or 2 x 10 m rectangular areas (plots or belts) sampled below the bottom edge of mussel beds in the same location each year, with plot size enlarged to 2 x10m at years or sites when Pisaster abundance was low. Belt replicates were spaced throughout the defined study site to capture the density of Pisaster just below mussel beds. In each belt, researchers carefully searched for and collected all sea stars present and then wet weighed and measured arm lengths (madreporite to tip of opposite arm). Sea stars were often abundant, so when we reached the threshold of 200 animals in site and sample date, we finished that transect, then discontinued weighing and measuring in subsequent transects. Instead, we counted the remaining sea stars in these transects to capture densities. When sea stars were sparse, we surveyed additional transects (up to 10 total) to assess size structure of 200 animals where possible, but these additional transects were not used for density calculations since they were not replicated over time. After measurements, all sea stars were returned to their respective belt plots. Overall, we performed 440 surveys over 24 years at these 8 sites, which included 1,582 transects and measurements of 143,241 individual sea stars.

We calculated density as the count in each plot divided by plot area, which we calculated separately for each life stage for measured animals (see below). We calculated average size in each transect as the average wet weight. Since time constraints, the SSWD pandemic, or field scale failure sometimes forced us to measure only arm lengths but not weights, we developed an equation for estimating weights based on lengths as [wet weight in grams = 0.417 * (arm length in cm)^2.574]. We calculated biomass density as the total weight of animals per meter² in each transect. This is a potentially more accurate measure of ecological importance since Pisaster can vary several orders of magnitude in size and since potential predation rates and top-down control of mussels can increase dramatically as sea stars grow.

Sea Star Wasting Surveys and Disease Phases

In 2014-2015, when the pandemic was at outbreak levels in Oregon, we quantified disease occurrence using frequent (biweekly to monthly) surveys at each site. For disease frequency surveys, we searched a large area (100s of m²) within the study site for all sea stars. We recorded if the animal was apparently healthy or not, and if not, recorded the symptom(s), including lesions, deflation, arm loss, arm twisting, losing grip and disintegration. We calculated percent diseased as the percent of the total animals that exhibited any SSWD symptom. After 2015, disease occurrence mostly was quantified in the belt transects supplemented by periodic wider surveys as above. Since we had never observed a prior outbreak of SSWD nor instances of disease symptoms, we assumed pre-SSWD percent diseased was 0.

Using our disease frequency and demographic data, we divided the SSWD outbreak into 4 phases, with Pre-SSWD (or Pre-wasting) as before 2014, During outbreak as 2014 when symptoms peaked, Post-SSWD (or Post-wasting) as 2015-2020 when small outbreaks continued to occur and adult populations were clearly still low, and Current as 2021-2024 when adult populations had begun to recover at several sites (though small outbreaks continued to occur). 

Categorization of Life Stages

We categorized different life stages of Pisaster into recruits (which we sometimes split into young-of-year recruits and older recruits), juveniles, and adults. Post-larval individuals (several weeks or months old) were not targeted by our surveys. We defined ‘young-of-year (YOY) recruits’ ranging in size from 0.01 to 1 g wet weight and 3 to 14 mm arm length.  We define older recruits as individuals of 1 to 5 g wet weight, ~1.4 to 2.6 cm in arm length, and based on our size structure histograms are ~2-3 years old. We defined juveniles as individuals 5 to 80 g and ~2.6 to 7.7 cm arm length (this corresponds to roughly 2-6 years old) and defined adults as >80g, and >7.7cm arm length.

Descriptions of size and density data processing are described in the associated paper - Gravem and Menge 2025. Metapopulation-scale resilience to disease-induced mass mortality in a keystone predator: From stasis to instability. Ecosphere. 2025;16:e70426. DOI: 10.1002/ecs2.70426

Size data are directly collected in the field by measuring all stars found in belt transects. Density of each transect is calculated from the size data. The number of stars in each transect, species, site and survey are totaled and then divided by the transect size.

* Sheet BT_Density of submitted file "BCODMO_BTMasterAnnot_2000-2024_2025-03-06_SAG.xlsx" was imported into the BCO-DMO data system for this dataset. Values "NA" imported as missing data values.   Table will appear as Data File: 990963_v1_belt-transect_density.csv (along with other download format options).

Missing Data Identifiers:
* In the BCO-DMO data system missing data identifiers are displayed according to the format of data you access. For example, in csv files it will be blank (null) values. In Matlab .mat files it will be NaN values. When viewing data online at BCO-DMO, the missing value will be shown as blank (null) values.

Supplemental Files:

* Validation Lists extracted from sheet ValidationList in BCODMO_BTMasterAnnot_2000-2024_2025-03-06_SAG.xlsx. Reformatted to not imply this is a table but rather unique lists of controlled vocabulary elements the study used.

* Site list exported from supplied SiteList_STARS.xlsx(version from 2026-05-11) Sheet1 after changing date format to ISO 8601. Attached to dataset as sitelist_stars.csv. Sheet2 contained column information which was added to the sitelist_stars.csv file description after modifications to match the data table (description for column "state" added, column name "LoggerCode_OSU" is "OldLoggerCode_OSU" in data table).

* Parameter (column) information updated from data submitter supplied file BT_Density_col-info.xlsx 2026-05-08.

None

Coverage: US West Coast; North bounding latitude: 45.00N, South bounding latitude: 38.00N

Algal Communities in Distress: Impacts and Consequences (ACIDIC)

Environmental stress models have recently been modified to incorporate the influence of facilitation to join negative effects such as predation, competition, and abiotic stress as determinants of community structure. Nevertheless, our empirical understanding of the processes that regulate the expression of facilitation effects across systems and the potential for facilitation to amplify or dampen the ecological consequences of climate change remains limited. This project focuses on facilitation dynamics in the broader meta-ecosystem concept, which hypothesizes that variation among communities depends not only on locally-varying species interactions and impacts of abiotic factors such as environmental stress and physical disturbance but also on regionally- and globally-varying ecosystem processes such as dispersal and flows of materials such as nutrients and carbon. The investigators will study the influence of a potentially critical facilitative interaction between coralline algal turfs and canopy-forming macrophytes including kelps and surfgrass in a rocky intertidal meta-ecosystem. The research will be conducted in a climate change context, with a focus on how the macrophyte-coralline interaction is influenced by ocean conditions, including factors driven by variable upwelling (temperature, nutrients, phytoplankton abundance, and light) and increases in ocean acidification, which vary in a mosaic pattern along the coast of the northern California Current (NCC) in Oregon and northern California.

The goal of the project is to test the hypothesis that the coralline turf-macrophyte canopy interaction is a cardinal interaction in the determination of low rocky intertidal community structure, and that disruption of this interaction would dramatically alter the structure and function of this kelp- and surfgrass-dominated assemblage. The project will take advantage of, and enhance, a research platform established across 17 sites spanning ~800 km in the NCC coastal meta-ecosystem with prior NSF funding that will at each site: (1) quantify ocean conditions, including temperature, nutrients, phytoplankton, light (PAR), and carbonate chemistry to document the response of community structure oceanographic variation across a meta ecosystem mosaic; (2) carry out field experiments testing the nature of the interaction between coralline algal turfs (primarily Corallina vancouveriensis) and dominant canopy species, the kelp Saccharina sessile and the surfgrass Phyllospadix scouleri; and (3) carry out laboratory experiments focusing on the mechanism of the interaction, specifically testing the effects of carbonate chemistry, light, temperature, and nutrients. Component (1) will employ both remote sensors deployed in the intertidal (fluorometers, thermal sensors, PAR sensors, and a recently developed pH sensor) and direct sampling (nutrients, phytoplankton, pCO2, and pH) to quantify the in situ exposure regime of benthic primary producers to resources, energy, and environmental stress across spatial scales. These metrics will be combined with a newly developed index for quantifying local-scale variation in upwelling intensity to characterize the linkages between climate forcing and ecosystem state. Coupling oceanography with our field and laboratory experiments will provide unique and valuable insights into how the current state of rocky intertidal ecosystems is likely to be altered in the future.

Intellectual Merit. The project will contribute one of the first studies to test the community consequences of varying upwelling and CO2 across an ecosystem scale. How these factors alter the direct and indirect interactions of key species is of fundamental importance in our efforts to learn how field ecosystems will respond to climate change. Such knowledge is crucial to our efforts to manage and conserve marine communities facing human-induced variation in climate.

Coverage: US West Coast; North bounding latitude: 45.00N, South bounding latitude: 38.00N

Collaborative Research: Scaling up from community to meta-ecosystem dynamics in the rocky intertidal - a comparative-experimental approach

The meta-ecosystem concept hypothesizes that the dynamics of ecological communities reflect interdependence between local-scale and ecosystem processes that vary across large distances. Thus, variation among communities depends not only on locally-varying species interactions and abiotic factors, such as physical disturbance, but also on regionally- and globally-varying ecosystem processes, such as dispersal and flows of materials such as nutrients and carbon. This study of rocky intertidal communities and the factors underlying their variation addresses the issue of meta-ecosystem dynamics. The goal of this project is to understand how variability in oceanographic subsidies, such as nutrients and phytoplankton, influences benthic community structure in the northern California Current Large Marine Ecosystem. Local-scale variation in upwelling along the Oregon and northern California coasts will be used to understand how changes in nutrients and productivity influence benthic-pelagic coupling, its effect on benthic species interactions, and ultimately rocky intertidal community structure. A conceptual model, in which the independent variable is seawater temperature (SWT), is used to predict how the dual effect of nutrients and light on marine benthic and pelagic primary production generates different community outcomes in the low intertidal zone. The two "endpoints" of community structure are a dominance of filter feeding invertebrates or macroalgae. The model predicts that with low (cold) SWT, nutrient and light availability is high, and macrophytes are dominant. Under very high nutrients and light, competitively dominant kelps will prevail and possibly facilitate stress-intolerant macroalgal species, and as nutrients and light diminish, kelp dominance should switch to dominance by surfgrass and foliose understory algae. With higher (warmer) SWT, conditions favor high phytoplankton production, leading to dominance by sessile invertebrates. High phytoplankton also creates low light and low nutrient conditions, negatively affecting growth of macroalgae and their ability to compete with sessile invertebrates. Research will be conducted at 15 sites nested within five capes spanning the 1300 km range of the study region. A water sampling program will quantify concentrations of nutrients and phytoplankton, field-deployed remote sensors will provide time-series estimates of light and chlorophyll a, and surveys will quantify community structure. Manipulative field experiments will test the role of species interactions on community structure and how interactions vary with ecological subsidies.

Website: http://www.eeb.ucsc.edu/pacificrockyintertidal/data-products/sea-star-wasting/

Coverage: Oregon coast

This study will investigate the ecological consequences of the decimation of sea star populations by wasting disease along the Oregon coast. Hallmarks of wasting disease are the formation of sores on the sea star that progress to cause loss of arms, and ultimately death of the animal. Wasting disease was reported in sea star populations including those of the purple sea star, Pisaster ochraceus, in British Columbia, Washington, and California as early as April 2013. In Oregon, wasting was first observed in April 2014, and by June 2014 rates of infection ranged up to 80%, and sea star abundance had declined. At that rate, many populations may disappear by the end of summer 2014. Prior research has shown that in the absence of the purple sea star, mid-shore mussel populations increase, and ultimately overgrow the sea weeds and invertebrates that occur low on the shore, reducing biodiversity. However, because disease events of this magnitude have never occurred along the entire coastline, it is unclear if the small-scale expansion of mussels observed previously will be a general result of this event. One possibility is that predators unaffected by wasting, such as whelks and crabs, will increase their predation effects and blunt the expected invasion of mussels to the low shore. The research in this project will evaluate this possibility by testing the role of these alternative predators. Broader Impacts include the training of undergraduate and graduate students, the involvement of coastal residents and the production of microdocumentaries and video to document the changing context of this ecosystem.

The research project is designed to test three hypotheses. First, that in the absence of Pisaster ochraceus, predation by whelks will increase in strength through increases in whelk abundance and in whelk size, and at least partially compensate for the absence of Pisaster. Second, the small sea star Leptasterias spp. will also expand its role as a predator through increased size and abundance, and expansion of its habitat beyond mussel beds. Although individuals of this sea star have been observed to suffer from wasting as well, the frequency so far appears low, and it seems likely this species may persist. Third, the crab Cancer productus, normally mostly a subtidal species, will expand its range into the intertidal and help to compensate for the loss of Pisaster. Tests of these hypotheses will include manual removal experiments (whelk removal, Leptasterias removal, removal of both and of neither), cage exclusion experiments (whelk exclusions), cage inclusion-exclusion experiments (Leptasterias inclusion, Leptasterias exclusion). Experiments will be replicated with appropriate controls, and done at multiple sites on the central Oregon coast that vary naturally in population abundances, rates of prey and predator recruitment, and oceanographic conditions. Results obtained under this unprecedented set of circumstances will deepen and expand our empirical understanding of the dynamics of an iconic ecosystem, and will help parameterize community models.

Additional Project Information: Sea Star Wasting Map

Coverage: West coast of North America

NSF abstract:

In recent decades, ocean ecosystems, long thought to be immune to change, have undergone disruptions to their structure, diversity, and geographic range, yet the actual underlying reasons for such changes in oceanic biota are often unclear. Coastal intertidal zones (i.e., the shore between high and low tides) have long served as important ecological model systems because of advantages in accessibility and ease of observation, occupancy by easily studied and manipulated organisms of relatively short lifespans, and exposure to often severe environmental conditions. This research will address the stability of a well-known rocky shore system along the Oregon and California coasts. Prior long-term research indicates that, although casual observation suggests these systems are stable, in fact, they may be on the cusp of shifting into another state, losing iconic organisms like mussels and sea stars, and becoming dominated by seaweeds. These changes might be comparable to losing trees and large predators from terrestrial systems. This study would result in the training of undergraduates and graduate students, including individuals from under-represented groups. Additionally, this study would include outreach to the general public.

The researchers will focus particularly on impacts of increasing and more variable warming on community recovery. For example, climate oscillations (e.g., El Niño), coastal upwelling, and particularly temperature have all changed in recent decades in ways leading to increased stress on intertidal biota. In apparent response, coastal ecosystems evidently have become less productive, organismal performance (growth, reproduction) has declined, and key dynamical processes (species interactions) have weakened. The new research will pursue these strong hints of an impending “tipping point” by (1) continuing the projects that led to the insights of increasing instability, (2) adding new projects that will pinpoint ecological changes, and (3) expanding the region of work to include locations in California. Research will assess whether or not sea stars recover from wasting disease, experimentally test if species interactions are indeed weakening, quantify the annual inputs of new prey and changes in abundance, diversity, stability, and resilience of intertidal communities, and document changes in the physical environment. Using field observations and experiments, the research will provide insight into impacts of environmental change, particularly warming, on the future of coastal ecosystems, and more generally, into possible future states of Earth’s ecosystems. Using these data, we will test the hypothesis that direct and indirect effects of climate change are driving, or may drive these systems into new, alternative states.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Website: http://www.piscoweb.org/

Coverage: West coast of North America from Mexico to Alaska

The Partnership for Interdisciplinary Studies of Coastal Oceans is a long-term ecosystem research and monitoring program established with the goals of: 

• understanding dynamics of the coastal ocean ecosystem along the U.S. west coast
• sharing that knowledge so ocean managers and policy makers can make science based decisions regarding coastal and marine stewardship
• producing a new generation of scientists trained in interdisciplinary collaborative approaches

Over the last 10 years, PISCO has successfully built a unique research program that combines complementary disciplines to answer critical environmental questions and inform management and policy. Activities are conducted at the latitudinal scale of the California Current Large Marine Ecosystem along the west coast of North America, but anchored around the dynamics of coastal, hardbottom habitats and the oceanography of the nearshore ocean – among the most productive and diverse components of this ecosystem. The program integrates studies of changes in the ocean environment through ecological monitoring and experiments. Scientists examine the causes and consequences of ecosystem changes over spatial scales that are the most relevant to marine species and management, but largely unstudied elsewhere.

Findings are linked to solutions through a growing portfolio of tools for policy and management decisions. The time from scientific discovery to policy change is greatly reduced by coordinated, efficient links between scientists and key decision makers.

Core elements of PISCO are:

• Interdisciplinary ecosystem science
• Data archiving and sharing
• Outreach to public and decision-making user groups
• Interdisciplinary training
• Coordination of distributed research team

Established in 1999 with funding from The David and Lucile Packard Foundation, PISCO is led by scientists from core campuses Oregon State University (OSU); Stanford University’s Hopkins Marine Station; University of California, Santa Cruz (UCSC); and University of California, Santa Barbara (UCSB). Collaborators from other institutions also contribute to leadership and development of PISCO programs.  As of 2005, core PISCO activities are funded by collaborative grants from The David and Lucile Packard Foundation and the Gordon and Betty Moore Foundation. Core support, along with additional funding from diverse public and private sources, make this unique partnership possible.

Website: https://www.nsf.gov/funding/opportunities/ltreb-long-term-research-environmental-biology

Long Term Research in Environmental Biology (LTREB)

Supports research for a period of 10 years or longer to generate an extended time series of data with a focus on evolutionary biology, ecology and ecosystem science.

Synopsis
The Long Term Research in Environmental Biology (LTREB) Program supports the generation of extended time series of data to address important questions in evolutionary biology, ecology, and ecosystem science. Research areas include, but are not limited to, the effects of natural selection or other evolutionary processes on populations, communities, or ecosystems; the effects of interspecific interactions that vary over time and space; population or community dynamics for organisms that have extended life spans and long turnover times; feedbacks between ecological and evolutionary processes; pools of materials such as nutrients in soils that turn over at intermediate to longer time scales; and external forcing functions such as climatic cycles that operate over long return intervals.