Sergeant Major Egg Patches
Look a little closer and you'll notice that the sergeant major intent on attacking you is darker colored than normal and very close by there's a bright purple patch, usually on the side of a rock. So what's this all about? Reproduction! During November to April sergeant majors are courting and laying eggs and this aggressive behavior is dad making sure no-one eats his kids. Spotting fish eggs underwater is fairly rare but once you spot a patch of these you'll notice dozens of others nearby.
When the eggs are bright purple they're freshly laid and over the next 6-7 days they will slowly change color as the embryo develops. Dad will stick around until the eggs hatch when presumably he'll go off to the pub for a well earned beer or two.
At Devil's Table the reef butterflyfish, seen above left, have a voracious appetite for these eggs even using divers as cover to launch a stealth attack. Recently I've been pecked on the head by a scrawled filefish who thought I was competition for this fishy delicacy!
Thanks to Tamsin Eyles for the photos.