Sponge Reef - Location of Sponge Reefs

Location of Sponge Reefs

Although hexactinellid sponges are found worldwide in deep seawater, the only place that they are known to form reefs is on the western Canadian continental shelf. Communities of Rosselid sponges called “sponge mats” are widely distributed; they are found in canyons in the North Atlantic, in the Canadian Arctic and on Antarctic continental shelves. There is also a reef formed of siliceous Demospongiae species off of Axel Heiberg Island in the Arctic ocean.

Four hexactinellid reefs were discovered in the Queen Charlotte Basin (QCB) in 1987-1988. Three more reefs were reported in the Georgia Basin (GB) in 2005. The QCB reefs are found 70–80 km from the coastline in water 165–240 m deep. These reefs cover over 700 km2 of the ocean floor.

Sponge reefs require unique conditions, which may explain their global rarity. They are found only in glacier-scoured troughs of low-angle continental shelf. The seafloor is stable and consists of rock, coarse gravel, and large boulders. Hexactinellid sponges require a hard substrate, and do not anchor to muddy or sandy sea floors.

They are found only where sedimentation rates are low, dissolved silica is high (43-75 μM), and bottom currents are between 0.15 and 0.30 m/s. Dissolved oxygen is low (64-152 μM), and temperatures are a cool 5.5-7.3°C at the reefs. Surface temperatures range between 6°C in April and 14°C in August.

Downwellings are common in Hecate Strait and Queen Charlotte Sound, especially in winter, but there is an occasional summer upwelling. These upwellings bring nutrient-rich waters to the sponge reefs.