No, it's not a lawnmower blenny. It's Parablennius intermedius ... called horned blenny in Australia. They do well in tanks, but can be a bit on the aggressive side. There are a number of more suitable blennies in your area. Check out the oyster blenny (Omobranchus anolius) on Google - they are common around oyster-covered rocks. This time of year you should be seeing juvenile tropical species in your area too, such as butterflyfishes (Chaetodon and Heniochus species mostly), various damsels, wrasses (Halichoeres, Stethojulis, Thalassoma, Coris, among others).
Tony