Evidence for a trophic cascade on rocky reefs following sea star mass mortality in British Columbia

The US Pacific Northwest and western Canada experienced a mass mortality of sea stars between 2013 and 2015. The sunflower star (Pycnopodia helianthoides), a previously abundant predator, began to show signs of a wasting syndrome in early September 2013, and dense aggregations disappeared from many sites in a matter of weeks. REEF surveyors certainly noticed, and the decline was reflected in the REEF database. The authors used the REEF database to document the decline regionally, along with a four-fold increase in the number of green sea urchins (Strongylocentrotus droebachiensis). The sea urchin increase also resulted in declines in kelp canopy coverage. This type of ecological change or trophic cascade, is where a change in one species impacts many others. Because of the long-term and wide-spread nature of the REEF survey program, our data have proven invaluable in documenting the impacts of the seastar wasting disease.