Sponge Reef - Destruction of Sponge Reefs

Destruction of Sponge Reefs

The reefs are susceptible to damage by fishing, especially bottom trawling and dredging. In typical groundfish trawling, a large net is dragged across the ocean floor, its mouth held open by two 2-tonne doors called otterboards. The siliceous skeleton of the sponges is fragile, and these organisms are easily broken by physical impact. The impacts of bottom trawling have been observed in three of the reefs in the QCB. Trawling damage appears as parallel tracks 70–100 m apart that may extend for several km. Each trawl track is 10 cm deep, 20 cm wide, and occurs at depths of 210–220 m. Sponges in the vicinity of trawl tracks are shattered or completely removed.

While less harmful, hook and line fishing as well as crustacean trapping may also damage the reefs. 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.

Breakage of reef sponges may have dire consequences for the recruitment of new sponges, as sponge larvae require the siliceous skeletons of past generations as a substrate. Without a hard substrate, new sponges cannot settle and regrow broken parts of the reef. It has been estimated that broken sponge reefs may take up to 200 years to recover.

In addition, offshore oil and gas exploration threatens the reefs. 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. 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.