Well... the drone hadn't been immediately eaten when it had entered the water. And the mass didn't seem to be moving or anything.

Niou peered at the video footage coming through and sent the drone closer. "It's... like... coral?" he said, confused. But it didn't seem to be moving, in any case. "Mr Oshitari, what do you think? I can take scans of it, but I'd need to use other drones."