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 29^th 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.