Tuesday, February 18, 2014

Invasive Sea Anemones Threaten the Health of Coral Reefs Due to Sunken Ships

Healthy coral reef- Picture by Kydd Pollock
Iron leached out from sunken ship with surrounding invasive sea anemone- Picture by Jim Maragos, USFWS 
In 2008, scientists began to notice the declining health of the Palmyra Atoll coral reef in the central Pacific due to several shipwrecks in the surrounding area.  Warming seas and ocean acidification were already affecting the health of the reef, but excessive growth of Rhodactis howesii due to leached iron from sunken ships further reduced the quality of the coral reef.  Iron is an essential element for many marine organisms, but in excess, invasive species like R. howesii can thrive.

R. howesii is a type of sea anemone that is very aggressive.  When excess nutrients like iron are available with no predators to keep populations in check, the anemones thrive.  R. howesii also preys upon coral, which further degrades the health of the coral reef. 

In September 2007, USGS researcher Dr. Thierry Work, Dr. Greta Aeby from the Hawaii Institute of Marine Biology, and Dr. James Maragos from U.S. Fish and Wildlife Service studied a shipwreck from 1991 on Palmyra Atoll in the Pacific Ocean.  The researchers discovered that R. howesii was growing in high densities surrounding the ship, and densities steadily decreased with distance from the wreck.  Since the atoll is isolated, runoff from agricultural or industrial activities is unlikely, so the shipwrecks are the only logical source of excess nutrients. 

With the sea anemone growing rapidly, it causes a change in the dominant life form of the reef and is referred to as ‘phase shift’.  Even though phase shifts can have long-term negative effects, eliminating organisms like R. howesii are an impossible feat, especially over a large area.  Rapid removal of shipwrecks to prevent reefs from being overgrown by invasive species like R. howesii is crucial to reef health. 

Remediation projects are currently being implemented to evaluate the resiliency of coral reefs after shipwrecks removal. On January 29th 2014, the Fish and Wildlife Service completed a $5.5 million conservation project to remove three wrecked ships, weighing a total of one million pounds, from protected wildlife areas in the Pacific Remote Islands National Wildlife Refuge. The shipwrecks caused miles of damage to the Palmyra Atoll and Kingman Reef.  With the reefs being home to 176 species of coral and 418 types of reef fish, protecting the damaged reef from further destruction was vital.  A team of 16 people cut and removed the wreckage from the coral reefs without causing further damage, bringing the salvage to California to be recycled. 

A representative of the remediation project stated, "We know Palmyra Atoll is resilient; it's one of the last remaining healthy coral reefs.  We've done some experiments with removal, and within three weeks we saw new species coming back to the area—mainly microscopic coral recruits.  These resilient areas can heal themselves when they get back on track."

Using Palmyra Atoll and Kingman Reef as controls, scientists can begin to understand how coral reefs heal.  It is possible that these examples can teach scientists in other parts of the world how to restore coral reef health.


  1. This was a very neat article! It is shocking to me that sunken ships can have such a negative impact. I am glad they were able to remove some of the wreckage, but as we read in your post that is very costly!

  2. I'm with Alison- I had no idea that sunken ships were causing any problems at all. In fact, I always used to think that the little critters in the ocean loved ships and stuff to swim in and out of and make homes and such! I was also surprised at how much the conservation is costing, but I'm happy that someone has taken measures in hopes to fix the damage that has been made. It would be a shame to see more coral in the ocean die- coral is what makes it so beautiful!