Fig. 1

Ostreobium in situ in the Ryukus. a Coral reef habitat where microfloras harboring Ostreobium spp. underlay live coral tissue (picture background) and limestone often covered by epilithic turf algae and crustose coralline algae (foreground). b Fragmented coral colony showing Ostreobium’s ‘green layer’ found below live coral tissue, here Porites sp. c Calcium carbonate colonized by Ostreobium sp. microsiphons (Scale bar approximately 20 µm)