Sponges on hammers

[muggle0981]

Not best pic

but what causes (believe sponges) to grow on my hammer

 

[KingTideCorals]

Usually the hammers head will provide some shade and coverage and the sponge most likely small when first introduced to the colony and over time has just taken over.

I saw a ReefBuilders video where they utilizied a water pic to blow out all the sponges on what I believe was a duncan colony