by Katie Barott, member of the Microbe Team
As everyone knows, when a ship goes aground on a coral reef, the corals and other benthic critters in its path get crushed. But, unfortunately, in areas like the Line Islands this physical destruction is the least of the damage.
The term “shipwreck” may conjure images of stormy nights of the distant, pre-technological past. The reality is that accidents still happen. Just three years ago, in 2007, a ship ran aground on Kingman. In the intervening years, the reef surrounding the wreck has disintegrated into a murky mess full of dead and dying corals with lots of black algae growing on the bottom. We headed out to the site in the Zodiac. As we descended to investigate the reef near the wreckage, it was as if we had suddenly been transported from Kingman to a different island. Gone was the pink frosting of the crustose coralline algae that help shape the reef, gone were the massive coral colonies, and gone was the clear water and 200 ft visibility. Instead we saw only a few remaining coral colonies—small, many looking diseased—struggling to survive despite the overgrowth of mats of thin filamentous cyanobacteria and algae. I had an eerie feeling as the sharks loomed in and out of view in the murky water.
We call these shipwreck sites black reefs because of the dark reddish-black color of the bacterial mats that thrive here. Kingman is not the only pristine reef afflicted by a rusting boat. In the ocean waters in this area of the world, iron is one of the key compounds that limits the growth of seaweeds (algae) and bacteria. As the ship continues to rust away atop Kingman Reef, its iron encourages the rapid growth of these nasty mats that annihilate corals. While this reef is actively grazed by an intact herbivore community, the grazers can’t keep pace with the rampant mats. Sadly, this black reef is spreading out for hundreds of meters from the epicenter of the wreck. It may take decades for the ship to completely disintegrate, and possibly hundreds of years for the corals to recover.
It must have been a bad day for those onboard in 2007, but for the reef the bad days are far from over.