5. Conclusion

Based on these results, together with data for Ocean Niño events as defined herein, we conclude that 2011 marked the most recent climate regime shift. The new climate regime is characterized by reduced abundance of numerous species, representing over 10% of all the seabed biota in this region. The 2011 regime shift was marked with eleven taxa dropping from detection as well as numerous taxa decreasing in abundance. There is no signal of global warming suggested by the absence of those eleven species, but the lowered abundance of other species and increase in warm water anchovies and brown rockfish may relate to overall temperature. The present suggestion is to define start-year for climate regimes based on the end of pairings of strong (anomalies >1.0) El Niño and La Niña events where ≤2 months separate such paired events. We are unable to assess the correct timing of the 1974 or 1977 regime shift owing to limited biodiversity data for that period, but our results support 1999 rather than 2001 as the start of the millennial climate regime.

It is noteworthy that the SSWD eliminated sunflower sea stars along much of the entire west coast of North America and is continuing in various localities today. Urchin abundance has similarly shifted along the coast, both from emergence of adults from seclusion and from reproductive success [16] so that kelp may go through a cycle of low abundance. Reliance of the spot prawn on Neoagarum as nursery habitat in the Howe Sound region [19] suggests that an ultimate cascade effect of the sea star wasting syndrome could be reduction of prawn abundance below levels supporting commercial harvest. This endpoint would give the best indication that urchin barrens really are significantly more prevalent than in any previous period, since urchin barrens always seem to occur at one or another small locality. Even with the current level of citizen science focused on sea star wasting, many areas remain uninvestigated, so the fate of the prawn fishery in Howe Sound and Strait of Georgia waters will be an important indicator of ecosystem status from the standpoint of Neoagarum kelp beds.

Ref. [16] discusses the densovirus die-off of various seastar species in the Strait of Georgia that resulted in the very high sea urchin abundance evident for the last several years. This may have driven cascade effects that reduced seaweed abundance and associated fauna. It is not clear, however, that all the biodiversity changes associated with this 2011 climate regime shift relate to the seastar collapse. It seems more likely that the anomalous "warm blob" followed by a record El Niño event may have affected overall ecosystem processes. The determination of how global warming interacts with regular Ocean Niño Index events remains a foremost concern for future observations and analysis.

Although caveats about global warming always need acknowledgment, the principal finding in this book chapter of close correspondence of biodiversity shifts to naturally occurring climate regime shifts is a positive sign. Both increases and decreases in species abundance tend to coincide with climate regime shifts that have occurred regularly as a fundamental aspect of weather and climate on earth. Examination of long-term biodiversity databases should include comparisons to ONI climate regime cycles.
