Monitoring of biodiversity may sometimes reflect human impacts on ecosystems, but analysis of biodiversity needs to account for naturally occurring trends as well. Biodiversity may provide more accurate definition of climate regime shifts than do physical oceanographic data, Using search programs for a long-term SCUBA taxonomic database (3865 dives) for Strait of Georgia seabed sites, 1,077 taxa were screened to select 171 rare or highly abundant taxa and to present the data according to climate regime categories. Ocean Niño Index climate regime shifts are defined here as the year of the end of the first La Niña closely paired with an El Niño by separation, where anomalies for both El Niño and La Niña exceed 1.0 on the ONI scale. For both rare and abundant taxa, patterns of increased or decreased abundance frequently correspond to years defining climate regimes. Cascading effects of climate regime shifts may occur via changes in community composition. The sea star wasting disease (SSWD) syndrome eliminated predators of urchins so that urchins have decreased abundance of a kelp species that is nursery habitat for spot prawns. We conclude that 2011 was a climate regime shift. This 2011 regime shift coincided with disappearance of 11 seabed species from our Strait of Georgia dataset, none of them at their southern range extreme. 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
