GLASS SPONGES OF BRITISH COLUMBIA
Department of Biological Sciences, University of Alberta
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Glass sponges are enigmatic members of the deep-sea fauna that inhabit shallow waters in only a few locations world-wide. They are found in ‘shallow water’ (less than 500 m) in only four locations world wide: Antarctica, some fjords of Southern New Zealand, some submarine caves in the Mediterranean, and the fjords and continental shelf waters of the Pacific Coast of North America. Glass sponges are unusual animals because their skeleton is of nearly pure glass (hydrated silica dioxide), and can be up to a meter in diameter; their soft tissue is also odd in that the majority consists of a giant multinucleated syncytium; cellular components are connected to the syncytium by cytoplasmic bridges that are typically plugged by a unique osmiophillic plugged junction.
Two readily distinguishable groups of glass sponges exist; those with a skeleton of spicules loosely held together by tissue [(Lyssaccine-'boot' sponge), and those which cement the spicules together into a fused robust scaffolding (Dictyonine-'cloud sponge')].
Dictyonine sponges are only found in the order Hexactinosida, and are often referred to as Hexactinosan sponges.
Sponges in this group can settle on the skeletons of previous generations and over time, form giant sponge reefs. Though sponge reefs were abundant during the Jurassic period (~200 mya) they were thought to be extinct until 4 sponge reefs were discovered in Hecate Strait and Queen Charlotte Sound, British Columbia, in the early 1990s. The fact that the primary reef forming hexactinosan sponges are only found in temperate Pacific coastal waters might explain the restricted distribution of sponge reefs. But what factors govern the distribution of glass sponges both vertically and geographically?
A study of patterns of distribution and abundance of glass sponges in B.C. fjords suggests that highest abundances coincide with water conditions of high dissolved silicate, low light, temperatures between 9 and 10°C and low suspended sediments.