Oestrogen pollutants in human sewage may be partially responsible for the decline of the world's coral reefs by interfering with their sexual rhythm.
Researchers have found evidence that the coordination of spawning among the tiny polyps that make up living coral is related to the female sex hormone.
Shannon Atkinson, of the Marine Biology Institute at the University of Hawaii, United States, told a conference on environmental hormones in New Orleans on Monday that it is not yet known whether oestrogen is a critical or peripheral element in the sex life of coral. However, if it was significant, then human pollution could be having a catastrophic impact.
"Many island people say that near to populated areas, coral cannot reproduce and the reefs are dying," she said. "We have focused on human sewage and have found much higher levels of oestrogens in the water in these areas," she said.
Together with her husband Marlin, professor of oceanography at the institute, Dr Atkinson has surveyed sex hormone concentrations around reefs across the Pacific, Australia and Florida. She ties this in with discoveries linked to the coral's sexual chemistry itself.
Corals must synchronise their sexual cycle so that gametes are released into the water at the same time. When this happens varies, but usually follows a predictable pattern, which is influenced by the phase of the moon - for example, Australia's Great Barrier Reef spawns four days after the first full moon in November.
Atkinson found that oestrogen levels in the coral tissues rise and fall according to this natural rhythm and are somehow bound up in the process.
"It is probably related to the development of gametes, though we cannot positively say this yet," she said. She speculated that should this prove to be the case, it is possible that oestrogen pollution from human sewage was interfering with this cycle and wrecking the coral's attempts at reproduction.