Coral reefs near shipwrecks in the central Pacific Ocean probably become overwhelmed with dark microorganisms because of elevated levels of iron in the water.

Credit: J. SMITH/F. ROHWER

Linda Kelly at San Diego State University in California and her colleagues studied three 'black reefs' (pictured, top) around the Line Islands, and compared them with nearby normal reefs (pictured, bottom). Live-coral coverage dropped from about 60% to less than 10% on the black reefs, and algal tissue from one of the sites contained high levels of iron, unusual for central Pacific waters. Sequencing the genomes of the reef's microbial populations revealed the presence of pathogens and genes involved in iron-related microbial virulence.

The team says that iron from the ships dissolves in the water, increasing the microbial growth that kills the coral. They call for the removal of shipwrecks from coral reefs.

ISME J. 10.1038/ismej.2011.114 (2011)