Acknowledgements

recruitment in absence of Neoagarum beds could result in a population in Howe Sound consisting of mostly females for the winter of 2017/2018. This would lead to expectation of very little successful fertilization of eggs, a negative feedback loop that would further exacerbate the limit to nursery settlement that results from low availability of Neoagarum kelp beds. The reduction in sunflower stars, however, started with the 2011 regime shift, then was exacerbated by the SSWD, with further cascades through urchins, kelp and prawns following. The present data compilation is the first to reveal the full decade of extraordinary sunflower star abundance during the millennial climate regime of 1999–2011, as well as the drop in abundance coincident with the 2011 regime shift (Figure 2). That drop in abundance coincident with the paired La Niñas of 2010–2012 could have resulted from some loss of condition factor during the cool conditions that then were followed by the SSWD event of 2013. A SSWD event with Pisaster in Oregon correlated with cooler temperatures rather than warmer [31]. We must note that the continuing SSWD of other sea star species such as Pisaster ochraceus in 2014 has only resulted in up to 80% mortality in populations [31]. This contrasts to the reduction to nil abundance, as occurred in the present observations of Pycnopodia helianthoides in Howe Sound (Figure 2) and in 1978 with Heliaster kubinjii in the Gulf of California [10]. Further, no discussion to date of proximate (SSWD) versus ultimate factors [31] has considered climate

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

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

regime shifts as a possible ultimate factor.

rather than 2001 as the start of the millennial climate regime.

5. Conclusion

78 Selected Studies in Biodiversity

Alejandro Frid assisted with manuscript review and editing. Jessica Schultz assisted with diving and manuscript preparation. Kris Moulton created the map of study regions. Portions of the diving for this work were funded by donations from members of the Howe Sound Research and Conservation Group of the Vancouver Aquarium Coastal Ocean Research Institute.
