Sponge reef
Sponge reefs were once a dominant landscape in the Paleozoic and Mesozoic sea, but are now very rare, and found only in waters off the coast of North America's Pacific Northwest region, more specifically southern Alaska, British Columbia and Washington.
They obtain nutrition from direct absorption of dissolved substances, and to a lesser extent from particulate materials.
[3] Although hexactinellid sponges are found worldwide in deep seawater, the only place that they are known to form reefs is between south east Alaska and off Grays harbor.
[5] There is also a reef formed of siliceous Demospongiae species off of Axel Heiberg Island in the Arctic Ocean.
[5] Hexactinellid sponges require a hard substrate, and do not anchor to muddy or sandy sea floors.
[6] 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.
[6] Downwellings are common in Hecate Strait and Queen Charlotte Sound, especially in winter, but there is an occasional summer upwelling.
The tendrils will later form the basal plate of the adult sponge that firmly anchors the animal to the reef.
Deep ocean currents carry fine sediments that are captured by the scaffolding of sponge reefs.
The sponges reached their full extent in the late Jurassic (201-145 million years ago) when a discontinuous reef system 7,000 km long stretched across the northern Tethys and North Atlantic basins.
[2][3] Observations by crewed submersible indicate that the fauna of sponge reefs differs from surrounding areas.
In typical groundfish trawling, a large net is dragged across the ocean floor, its mouth held open by two 2 tonne doors called otterboards.
When the fishing gear is hauled to the surface, the lines and traps drag along the ocean floor and have the potential to break corals and sponges.
Broken sponge "stumps", as well as those with abraded sides, were found in regions where line and trap fishing took place.
The government of British Columbia has lifted a moratorium preventing exploratory drilling and tanker traffic in Hecate Strait and Queen Charlotte Sound, and the area has been leased by the oil and gas industry.
[3] Even if exploratory drilling is not done on or immediately adjacent to the reefs, it may still have a negative impact by increasing the amount of sediment in the seawater, or through hydrocarbon pollution.
[4] In 1999, Fisheries and Oceans Canada requested that groundfish trawlers voluntarily avoid the sponge reefs.
[10] The management plan recommended that an additional 9 km (5.6 mi) buffer zone around the reefs be added to the existing groudfish trawl closures.
[3] Although MPAs may be more effective than fishery closures for long-term protection of the reefs from bottom trawling, the oil and gas industry would still pose a threat.
However, in 2011, the ministry withdrew support for the process in favour of greater consistency with ocean planning on the other coasts of Canada.
