Evidence for a trophic cascade on rocky reefs following sea star mass mortality in British Columbia
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| Authors: | Schultz, JA; Cloutier, RN; Côté, IM |
| Year: | 2016 |
| Journal: | PeerJ 4 Article Link (DOI) |
| Title: | Evidence for a trophic cascade on rocky reefs following sea star mass mortality in British Columbia |
| Abstract: | Echinoderm population collapses, driven by thsease outbreaks and climatic events, may be important drivers of population dynamics, ecological shifts and biodiversity. The northeast Pacific recently experienced a mass mortality of sea stars. In Howe Sound, British Columbia, the sunflower star Pycnopodia helianthoides a previously abundant predator of bottom -dwelling invertebrates began to show signs of a wasting syndrome in early September 2013, and dense aggregations disappeared from many sites in a matter of weeks. Here, we assess changes in subtidal community composffion by comparing the abundance of fish, invertebrates and macroalgae at 20 sites in Howe Sound before and after the 2013 sea star mortality to evaluate evidence for a trophic cascade. We observed changes in the abundance of several species after the sea star mortality, most notably a four -fold increase in the number ofgreen sea urchins, Strongylocentrotus droebachiensis, and a significant decline in kelp cover, which are together consistent with a trophic cascade. Qualitative data on the abundance of sunflower stars green urchins from a citizen science database show that the patterns of echinodermabundance detected at our study sites reflected wider local trends. The trophic cascade evident at the scale of Howe Sound was observed athalf of the study sites. It remains unclear whether the urchin response was triggered directly, via a reduction in urchin mortality, or indirectly, via a shift in urchin distribution into areas previously occupied by the predatory sea stars. Understanding the ecological implications of sudden and extreme population declines may further elucidate the role of echinoderms in temperate seas, and provide insight into the resilience of marine ecosystems to biological disturbances. |
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