How Do Shipwrecks Affect Marine Life and the Environment?

Accidental shipwrecks often come loaded with toxic materials that leach into the environment where they are challenging to remove. Shipwrecks also frequently occur when a ship crashes into hidden coral reefs, damaging particularly important marine habitats. While many shipwrecks damage the marine environment, some shipwrecks are intentionally placed underwater to create new habitats. Although intentionally sinking ships is criticized by some as greenwashing, research suggests "artificial reefs" can be created by shipwrecks under the right condition. By creating new places for fish and other marine life to live, shipwrecks could help mitigate the loss of reef ecosystems.

Pollution and Habitat Destruction

When ships are abandoned in the ocean or sink due to catastrophic failures, they inevitably impact the surrounding environment. When large vessels scrape the seafloor, they can easily damage over 10,000 square feet of ocean habitat. Additional, long-term effects can arise from the contents of sunken ship, like the ship's cargo, fuel, and even its paint.

Sea Diamond Shipwreck

In 2007, the MS Sea Diamond cruise ship ran aground on a volcanic reef in the Aegean Sea. Less than a day later, the ship sunk into the caldera of the ancient, underwater Santorini caldera.

Aboard the shipwrecked Sea Diamond carried an estimated 1.7 tons of batteries and 150 cathode ray tube televisions. Together, these manufactured goods and the ship's electrical equipment contain around 80 grams of mercury, 1,000 grams of cadmium, and over 1 ton of lead. Other heavy metals, like copper, nickel, and chromium, are present in the sunken ship's hull. Over time, these heavy metals will leach into the surrounding seawater or turn into salts that can contaminate the sand below.

While low concentrations of heavy metals occur in seawater naturally, a study of the area around the Sea Diamond shipwreck three years after the cruise ship ran aground found concentrations of lead and cadmium that exceed safe thresholds set by the Environmental Protection Agency. Given the time it takes for metals to corrode, the study's authors predict heavy metal concentrations will continue to increase in the area.

The Sea Diamond remains underwater today, where it continues to harm the environment. While a pollution barrier is in place, critics say it's not enough to mitigate the shipwreck's damage. In December 2019, the Greek government began to move forward with a project to remove the wreckage before promptly halting all efforts weeks later.

Rena Shipwreck

In October 2011, a container ship known as the MV Rena ran aground on Astrolabe Reef off the coast of New Zealand. Shortly after the collision, the 700-foot ship began leaking oil. Four days after the shipwreck, enough oil had spilled to form a 3-mile slick. The container ship's oil killed an estimated 2,000 seabirds. Over 300 oil-coated penguins were rehabilitated by wildlife rescue teams following the oil spill.

While the oil spill resulting from the MV Rena shipwreck was relatively minor overall, Astrolabe Reef, where the wreck occurred, remains seriously damaged today by the ship's cargo. Studies of the area in the years following the shipwreck have found heavy metals, oil products, and toxic chemicals in the reef's sediments, surrounding seawater, and within marine life. While much of the oil was cleaned up or degraded in the environment, contaminants stored among the ship's cargo will remain in the environment for much longer. For instance, one of the containers aboard the Rena was carrying over 20 tons of granulated copper pieces that piled onto Astrolabe Reef when the ship's hull ruptured. Copper is known to be toxic to marine life, but the fine pieces have been impossible to clean up entirely.

The ship itself is having a lasting effect on the reef as well. The MV Rena is covered in chemical paint used to prevent marine life from growing on boats and causing deterioration. While "anti-fouling" paint is still commonly used today, the type of chemical paint deterrent used by the MV Rena includes Tributyltin, or TBT, which is particularly effective at killing sea life. The chemical was so effective that its use in anti-fouling paints was banned in 2008. Ships already coated with TBT, like the MV Rena, can continue to operate so long as they do not re-apply the banned TBT-containing paint. As the MV Rena scrapes across the reef, more TBT is released into the environment.

New Habitats

Coral reefs and kelp forests are teeming with marine life due, in part, to their complex landscapes. Compared to areas with just a sandy seafloor, reefs and kelp forests provide lots of nooks and crannies for marine life to live and hide. Shipwrecks can have a similar effect on the underwater world by adding new structures for marine life to inhabit.

The benefits a shipwreck can provide to the marine environment vary a great deal on where a ship sinks and the ship's composition. For example, while a shipwreck that lands on top of an existing reef can damage large areas of existing marine habitat, a shipwreck near an existing reef can provide new habitat for marine life in the area.

In addition to creating habitat for marine life, shipwrecks can also create new places for scuba divers to visit. If divers visit shipwrecks instead of natural reefs, the reefs and their inhabitants could benefit.

Bellucia Shipwreck

The Bellucia, a steel-hulled cargo ship, sunk in 1903 near Rasas Islands off the coast of Brazil after accidentally striking a reef. The ship remains in place in two pieces about 85 feet deep. Today, the ship is considered an important area for fish feeding and spawning and is used locally by artisanal fishers.

A second steel-hulled shipwreck, the Victory, is located near the Bellucia, but sunk in 2003. Unlike the Bellucia, the Victory was intentionally sunk to create habitat. The ship was stripped before it sunk, eliminating nearly any materials on board that could harm marine life.

Even though the Bellucia sunk 100-years before the Victory, a 2013 study comparing fish diversity at the two wreck sites to nearby natural reef ecosystems found neither of the shipwrecks hosts a diversity of fish akin to that of natural reefs. The study showed how even a 100-year-old shipwreck cannot provide habitat of equal quality to much older reefs. While it's possible both the Bellucia and the Victory will continue to support a greater diversity of marine life over time, the creation of artificial reefs through shipwrecks cannot rapidly replace the loss of natural reefs.