Hmmm very interesting ! the concentric rings in the middle remind me of the holes seen at mud geysers but I dont know enough about the geology of seagull island (never heard of it ?) to say that is what it is , also some jelly fish fossils have this shape but they are quite rare and I dont think they would have fossilised in this rock as it looks quite disturbed ( in a sedimentary context) .Another possibility is some kind of algal/stromatolite formation. I cant tell what type of rock that is, it looks like a fine grained sedimentary rock ?
p.s attached photo of mud geysers for comparison (from google search not my own photo)