Black Reef Risk: How Sunken Metal Shipwrecks Attract Coral Destroying Invasive Species

In many parts of the world, there has been a debate about what to do with ships at the end of their life. Some environmentalists have campaigned for them to be safely dismantled, toxic materials removed, and their recyclable materials re-used to be part of a ‘circular economy,’ whereas in other cases, there is a debate whether ships can and should be sunk in the ocean.

Such decisions should not be taken lightly, and there is a growing amount of scientific research that reveal a lot of unintended consequences from well intended actions in different parts of the world.

In a handful of well-designed projects artificial reefs have been created from large industrial structures and old boats as habitats for fish populations in many previously heavily polluted industrial areas. However, just because one sees some biological growth, it doesn’t mean this is a sign of resurgence. It could be the start of something far deadlier. 

In every single case where an artificial reef has been created, this has followed years of careful cleaning and decontamination of a wreck (particularly the toxic anti-fouling paints used around the hulls of vessels), as well as careful planning and surveying of site of reef, before deciding where to release the wreck, and how to do so in a safe way without the deep water currents taking metal particles into areas that could create additional pollution and harm. 

There are also clear international laws around Marine Pollution and dumping in the sea (called Marpol), that the UN Agency responsible for shipping, the International Maritime Organization, governs. This is the very organization providing advice on managing the wreck of the Wakashio. 

Decades of pollution from rusting metal wrecks

Despite the few comprehensive scientific studies of the full impact of artificial reefs (and it is too early to say the true impact), there are even more concerning lessons from poorly planned and executed sinking of wrecks in tropical reef environments, that have ended up causing decades of pollution in some of the most pristine locations. They then had to be removed years later at the cost of millions of dollars and expensive heavy lifting equipment.

Here are some cautionary tales from the famous Palmyra Atoll National Wildlife Refuge, close to Hawaii in the Pacific Ocean, and one of the largest reef systems in the region. 

Artificial reef causing harm 20 years later

Fishing vessel, Hui Feng No 1 was a 121 foot fishing vessel was intentionally grounded in 1991. It ended up unintentionally creating an artificial reef and becoming a habitat for other marine life. After decades of damage and the growth of harmful invasive corals that created the risk of a ‘black reef’ phenomenon amid the endemic pristine coral reefs of Palmyra Atoll Reserve, the wreck had to be removed in 2013 at the cost of $5.5 million. As a size comparison, the MV Wakashio is almost ten times longer at 1000 feet, making it one of the largest vessels in the ocean.

It took many years from the US Fish and Wildlife Service to remove the Hui Feng No 1 wreck and provides an important lesson why it is almost always more important for the salvage and removal of a wreck to happened shortly after a vessel is grounded than ever to sink it.

Leaving the vessel on the reef for so long could be considered a huge mistake and as the wreck degraded, it leached nutrients into the environment (iron and other elements released as the ship rusted) like a slow release fertilizer.

Destructive and invasive coral can create ‘black reef’ phenomenon

Palmyra is a low lying coral atoll in the central Pacific, and naturally has very low amounts of iron in the surrounding environment. The iron (and other unknown nutrients), that were released into the water, fueled the growth of a coral killing sea anemone called a corallimorph. 

Sea anemones are a group of marine, predatory animals of the order Actiniaria, named after a land-based plant, the anemone because of their colorful appearance. Corallimorphs are soft and fleshy and have individual polyps.  This invasive species radiated out from the wreck and spread to cover over 2 miles of coral reefs. 

The wreck, and the nutrients released as the hull rusted over time, causing a ‘phase shift’ from an endemic coral dominated ecosystem with 80-100% coral cover, to one dominated by the invasive corallimorph. The corallimorph smothered everything on the seabed that could not move, either directly killing it or out competing it for space.  This part of the ocean floor is called the ‘benthos’ and many unique and undiscovered species live here.

In some places the corallimorph is a monoculture, with no coral or algae in sight.

Once the wreck was removed the invasive corallimorph in the area surrounding the wreck naturally died off.  The wreck was very hard to remove because it could not be re-floated, and took some creative engineering and cutting it up into pieces, putting the pieces on a barge and shipping the pieces to the US mainland. It was very costly and would have been a fraction of the price if the salvage and removal had happened shortly after the ship had grounded.

Not an isolated incident

Palmyra is not an isolated case where a shipwreck, or the large amounts of metal added to, or left in the environment, has caused a phase shift that has destroyed coral reefs.  Shipwrecks and derelict metal on reefs cause "black reefs," where a non-dominant benthic species grows out of control, and kills all other sessile species on that live on the sea floor around the reefs. Sessile species are any organism that is fixed to the underlying rock or coral (the substrate) and cannot move around or ‘walk away.’  So it is not just plants, but also corals, giant clams, tube worms, algae, other non-mobile invertebrates. 

Here are three examples of ‘Black Reef’ phenomenon from the Pacific:

• This has been seen at Kingman Reef with a fleshy macro-algae covering the reef after a vessel wrecked there.  
• A shipwreck at Rose Atoll, in American Samoa caused a “black reef” due to a cyano-bacteria smothering the reef. 
• Derelict metal gear and ships sunk during WWII around Howland and Baker Islands have caused “black reefs” of corallimorph.

‘Rust island’

Other toxins can also be released in the deep ocean environment. A US military barge was nicknamed ‘rust island’ due to its highly degraded condition, was grounded near the Western Lagoon of Palmyra Atoll National Reserve in the 1950s. Over the subsequent decades, as the outer layers degraded, some of the engine components and propellers remained, amid piles of metal scale. 

This degradation was being absorbed by some of the larger, deepwater species in the areas such as Blacktip Sharks. The full impact of how these heavy metal toxins enter the food supply chain is only just being understood using the latest genomic testing.

The list goes on, and there are many well documented scientific papers on this, such as this scientific paper published in the ISME Journal entitled, “Black reefs: iron-induced phase shifts on coral reefs”.

Value of rare life on the seabed

Years of environmental work and advanced marine science has gone into ensuring that the ocean is not used as the world’s dumping grounds. The world is only just beginning to discover the true value of life on the ocean, as it faces other pressures from humans such as climate change and industrial scale overfishing.

For years, humans believed that the bottom of the ocean was an empty desert. Now, with new submersibles and DNA sequencers, scientists have found some of the most promising medicines from organisms on the ocean floor – ones that can even be contain the cure for coronaviruses like the pandemic we are experiencing.

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2020 to 2030 was supposed to be the UN’s Decade of Ocean Science under UNESCO. Humans have only had a good understanding of 0.05% of the ocean floor where they have visited, photographed or surveyed to 1 meter resolution. 

This is the unexplored new planet sitting right under our noses. There is so much to learn, rather than simply assume it is a barren desert out in the deep ocean.

Debate over whether to sink the large Japanese Iron Ore vessel in the Indian Ocean

Over the past month, a debate has been raging in the Indian Ocean over what to do with a large Japanese Iron Ore transport vessel, the Wakashio, the largest class of vessel in the ocean. Satellite imagery captured the broken forward section of the 300m long Japanese vessel, the Wakashio, being towed away from the coast of the Indian Island of Mauritius on 19 August. 

However questions have also been raised about its direction, intention and what would happen if a vessel of this size was sunk at sea in a place where deep ocean currents could bring any contaminating materials still left on the vessel toward fragile ecosystems, or impact the complex biological food chains that may exist at such depths and in locations that whales come seasonally as part of an annual migration.

The International Maritime Organization also issues very strict guidelines on any dumping at sea, called Marpol. Lawyers and Environmentalists will no doubt be starting to keep a very close eye on the activities, records and decisions, of who did what, and what potential legal liabilities have now arisen from any decision to sink the Wakashio, without a full Environmental Impact Assessment of all options that could be considered.

As Greenpeace Africa pointed out in a statement yesterday, the two support vessels that had been towing the vessel were Malta-flagged vessels, Boka Summit and Boka Expedition. As Malta is a signatory to the Marpol convention, both are also subject to this scrutiny.

With regards to the Wakashio, satellite imagery does not show significant amount of cleaning having taken place around the vessel since it was stranded off the coral reefs of Mauritius on 25 July. The Wakashio was one of the largest vessels ever built. Owner of the vessel Nagashiki Shipping, has been approached for a comment on the list of materials that had been left on board and their assessment on the long term effects this could have in the ocean where through which the Wakashio was travelling. To date, the company have not responded whether they were supportive of any decision to scuttle the vessel.

It looks like the curse of the Wakashio will continue to haunt the Indian Ocean, until there is greater transparency around this story and a credible science-based approach to any cleanup.

This is not just a story about a lost Japanese Iron Ore vessel, but an illustration of an industry that has shied away from true international scrutiny.