Despite a recent expansion in the geographical focus of studies on coral reproduction, there remain many regions in the Indo-Pacific, such as Melanesia, where research is limited. For example, although New Caledonia in southern Melanesia is home to the world’s second largest barrier reef, which has recently been given UNESCO World Heritage listing, almost nothing is known of the reproductive biology of the coral fauna there, in particular the timing of spawning. In this study we sampled Acropora assemblages in November 2004 to test for reproductive synchrony at eight sites in New Caledonia separated by up to 200 km. In total, 80% of 1,055 Acropora colonies sampled contained mature oocytes, and 34 (92%) of 37 species sampled had at least one mature colony. These data demonstrate that reproduction in Acropora is highly synchronous over a large scale in New Caledonia and suggest a multispecies spawning event following the full moon in November coincident with the mass spawning period on the Great Barrier Reef, Australia. The high synchrony of reproductive effort implies that even a brief halt of activities that threaten fertilization and early development of coral propagules, such as discharge of liquid waste from ore processing, could have a major mitigating effect on the potential damage to these globally valued reefs.