Scientists investigating the highly destructive stony coral disease, which has infected reefs in South Florida and the Caribbean, have zeroed in on a culprit behind the unpredictable spread of the disease: ballast water from big ships. As WGCU reported, investigators are now poring over shipping records housed at the Smithsonian to confirm the connection and better contain it.

What Is Stony Coral Disease?

As NOAA explained,

• In September 2014, researchers began noticing that certain stony corals along the Florida Reef Tract weren’t doing well. The Florida Reef Tract stretches approximately 360 miles in an arc along the Florida Keys and southeastern Florida.
• Off Virginia Key, in Miami-Dade County, corals were showing “small circular or irregular patches of white, exposed skeleton devoid of tissue,” explains Dr. Andy Bruckner, research coordinator for Florida Keys National Marine Sanctuary.
• From there, the tissue would slough off, leaving the stark white skeleton exposed until algae colonized it. The disease, he explains, “radiates across the colony and outward.”

Solving the Mystery: WGCU explained that coral biologists got their first inkling that stony coral disease might be unlike other diseases that waxed and waned with temperatures when it lasted nonstop through the winter seasons. They confirmed it was waterborne and suspected it was caused by a bacteria. However, they struggled to determine other factors including where it came from.

Then, just recently, stony coral disease spread to the U.S. Virgin Islands after a ship there made an unauthorized release of ballast. 

What is Ballast Water? According to the USDA, ballast water is one of the major pathways for the introduction of nonindigenous marine species as well as toxins and disease. Ballast water is fresh or saltwater held in the ballast tanks and cargo holds of ships. It is used to provide stability and maneuverability during a voyage when ships are not carrying cargo, not carrying heavy enough cargo, or when more stability is required due to rough seas.

Why This Matters: By 2024, ships will be required to have onboard treatment systems to clean water under a 2004 treaty administered by the International Maritime Organization. However, scientists must test if these treatment systems are capable of killing story coral disease. The disease, unlike coral bleaching, kills corals entirely so that they cannot come back. 

In countries like the U.S., the Coast Guard can enforce that ships release ballast water far enough offshore so as not to disrupt ecosystems. However, in poorer nations like that of the Caribbean, a lack of resources can prevent them from enforcing these rules. Those countries could also suffer disproportionately because they rely so heavily on their reefs for both tourism and food.