Logging hundreds of images, in the field, bleary eyed, late at night, is not my strong suite and so it was that I recently discovered a curious mistake whereby a “coral disease” on closer inspection turned out to be a sponge – read on! This article illustrates some sponge-coral interactions from the Lizard Island area of the northern Great Barrier Reef which the novice diver might casually misinterpret as coral diseases. While not diseases these competitive interactions are often fatal to the coral.Note: the images in the galleries below will beg the question “what sponge is that”. Long ago I learnt that sponge taxonomy was a dark art. As I did not collect tissue specimens for microscopic examination it is not reasonable to expect colleagues to provide accurate names for the sponges shown below based on images alone – so – all names are “indicative”. That said I am deeply indebted to the following people for their time and assistance in field work and / or providing information for this article: Prof Bette Willis, (James Cook University), Dr Christine Schönberg (Australian Institute of Marine Science), Dr John Hooper (Queensland Museum), Dr Rachel Pears (GBRMPA), Dr Klaus Ruetzler (Smithsonian Institution), Lizard Island Research Station and photographer Phil Woodhead.