Resistance and Resilience of Ecosystems to Sea Star Wasting Disease
Though unfortunate, SSWS resulted in an ideal natural experiment. Because it caused the disappearance of species over a massive geographic area, we can investigate how important those species are throughout most of their ranges. Decades of research show that Pisaster ochraceus is the archetypical “keystone species” and can control the biodiversity of the intertidal ecosystem by eating mussels, thereby freeing up space for other animals and algae. Will we see a coast-wide takeover by mussels and subsequent decline in biodiversity? So far, we are seeing takeover by mussels in some places and not others, showing that things like mussel recruitment and growth may be prerequisites to keystone effects, and that the keystone concept may not apply everywhere. By examining these communities, we can understand mechanism that enable any ecosystem to resist change after losing a predator. Some of these communities also may be resilient to the outbreak, because an unprecedented number of young stars have arrived on shore.
Long-Term Monitoring of Intertidal Sea Stars
Intertidal sea star populations have been monitored for nearly 3 decades at sites ranging from Southeast
Alaska to Southern California by the Multi-Agency Rocky Intertidal Network (MARINe), a large
consortium of research groups working together to collect compatible data that are entered into a
centralized database. This extensive data set allows us to track natural variation in the abundance and
size structure of the ochre star, Pisaster ochraceus—the most abundant intertidal sea star on the outer
coast. These “baseline” data allowed for early detection of SSWS, and have been critical for assessing
declines and subsequent recovery of sea star populations along the entire west coast.
Citizen Science Monitoring for SSWS and Sea Star Population Trends
Building upon their long-term sea star monitoring effort, MARINe (see above) developed a citizen
science monitoring program to help fill in gaps in study areas and more effectively capture presence and
emergence of SSWS. This program is 2-tiered—participants can choose to submit basic observation data
about the health of sea star species anywhere along the coast using an online form, or they can establish
a long-term monitoring site (intertidal or subtidal) at which sea stars are counted and measured within
fixed areas at regular intervals throughout the year. Observational data have been instrumental in
tracking emergence of SSWS along the coast and long-term monitoring data are directly compatible with
the broader MARINe monitoring effort, thus greatly expanding our ability to document changes in sea
star populations coast-wide.
The coastwide sea star wasting disease event was made evident to many people through
social media and the direct observation of dying organisms on our coast. This provided
an opportunity for the Oregon Zoo to team up with The Nature Conservancy to tell the
story of the sea stars through a video and produce a teachable moment about life on our
rocky shores and what scientists are doing to study it. The video was posted on the
Oregon Zoo and TNC websites in August 2018 and had nearly 1 million hits in two
months. It can also be viewed at the Zoo’s Education Center.