Shipwrecks as artifial reefs

They are not only a great diving spot and nice underwater photography playground, wrecks also provides what sessile sea creatures crave most in a habitat: a hard substrate on which to live! While wooden wrecks will typically disintegrate after some time, the more modern metal wrecks have proven to be a perfect resting spot for many stationary ocean dwellers. As many of the large (sessile) organism begin their life as tiny, planktonic drifters, floating through the oceans currents – if the first thing they come across is a shipwreck, they’ll treat it much like they would a rocky outcrop.

Soft corals growing on a shipwreck in the Red Sea

In addition to the substrate they provide, wrecks are also an elevation above the seafloor and into the current. Mostly sessile organisms are looking for food are more likely to survive if they can obtain a meal while expending as little energy as is possible. If they can therefore find a spot where they can easily pick up the past-drifting food, it is perfect for them. For that reason, wrecks located in regions with high water currents are often especially beautifully overgrown [1].

Ann Ann Wreck close to Jeddah in the central Red Sea

But besides that, the corroding material itself can establish a good environment for calcifying organisms, such as corals to grow! Some studies of tropical corals have shown higher growth rates in the presence of an electrical field due to the increased abundance of dissolved mineral ions (such as calcium) for calcification. Since the metal components of shipwrecks often produce electric currents, these wrecks might create conditions favorable to higher-than-normal growth rates [2,3]. This could be an explanation why, especially burned-out shipwrecks which are lacking the protective layer of coating (and therefore corrode more easily) are often especially fast overgrown by corals and other incrusting and calcifying organisms [3].

Overgrown ladder at the Chicken Wreck, close to Jeddah in the central Red Sea

That is also why metal ship wrecks are some of the oldest and most well developed artificial reefs. Best examples are the warships from World War I and II, showing how the ocean can claim man-made structures and create a living ecosystem. Sometimes, these old wrecks are so covered in corals and marine life that they are almost unrecognizable as such and can only been identified through special technologies or even by accident during drilling or dredging operations.

Although coral reef organisms have been shown to grow well on these steel structures, there is also some concern that iron and other, usually limiting nutrients can also favor algal or even bacterial growth. That is why purposefully sunk wrecks do require environmental and safety preparations before they can be deployed.

Cable wreck close to Jeddah in the central Red Sea

But also other structures, such metal platforms can serve as artificial reefs as it can be nicely seen at this training platform at a diving resort in the Red Sea.

References:

[1] Baynes, Tracy W., and Alina M. Szmant. "Effect of current on the sessile benthic community structure of an artificial reef." Bulletin of Marine Science 44.2 (1989): 545-566.

[2] Hilbertz, Wolf. "Electrodeposition of minerals in sea water: Experiments and applications." IEEE Journal of Oceanic Engineering 4.3 (1979): 94-113.

[3] Goreau, T. J., et al. "Restoring coral reefs, oyster banks, and fisheries by seawater electrolysis: coastal zone management and tourism applications." Oceans 2003. Celebrating the Past... Teaming Toward the Future (IEEE Cat. No. 03CH37492). Vol. 2. IEEE, 2003.