Sea Life Flourishes On Sunken Ships

After sinking 18 ships off British Columbia's southern coast for recreational diving, the question arises as to whether the overall ecological benefits of the artificial reefs outweigh the losses. With most the underwater wrecks lying in 10 to 40 metres of water, they become fully colonized by sponges, shrimp, seaweed, sea anemones, tubeworms and other sea organisms within two years.

The habitat attracts numerous fish, particularly copper rockfish, along with sculpins, perch and lingcod. Divers have observed anywhere from 25 to 96 species of marine life on BC's artificial reefs, considerably richer than nearby waters.

On the other hand, life in the sea bottom underneath a sunken vessel is smothered. The artificial reefs in BC range from a 5 m log dozer to a 134 m navy vessel, creating a total footprint of about 1 ha, but the effect could be 2 to 3 times that size. Although not specifically examined in BC, studies elsewhere show that on balance an artificial reef adds considerably to an ecosystem's productivity.

Perhaps the most detrimental impact on sea animals is the explosion used to sink a ship. Lately these have been enhanced for public show with gunpowder and jet fuel. At one sinking, dead fish and panicking seals were observed nearby. Shock waves could affect fish within 200 m and mammals 500 m or farther away.

The first ship deliberately sunk for the enjoyment of scuba divers in BC was in 1980 at Howe Sound's Porteau Cove. The site is now a provincial park featuring six submerged vessels. Other artificial reefs lie near Sechelt, Victoria, Nanaimo, Campbell River and Port Alberni.