2. Materials and methods
2.1. Study site
Our study was conducted in the Strait of Georgia at Galiano Ridge – an underwater ridge that contains a discrete and unique habitat of reef-building glass sponges. The Galiano Ridge (48° 54′ 51″ N, 123° 19′28″ W) is a submarine crest running in a northwest-southeast direction parallel to the eastern shoreline of Galiano Island. The glass sponge reef discontinuously covers an approximately 5–6 km stretch of the ridge north and south of Active Pass (Conway et al., 2007 and Chu and Leys, 2010). Dissolved silica levels in the waters above and around this sponge reef are approximately 50 μmol/L (Chu et al., 2011). Dissolved oxygen levels in the area are known to range from 140 to 210 μmol/L (Johannessen et al., 2014).