The subject is the dominant fucoid brown algae growing on the rocky side of this very shallow subtidal channel.
The darker brown species dominant in frames (especially in image 1) is the subject for ID.
@fionaoutdoors and @marinejanine,TIA!( I'm suddenly paranoid about Wakame, but I'm quite sure this is native Kelp)
Growing along edge of pontoon in fully marine habitat.
Sighting and photos (c) amegilla_sa.
Field Notes - Was snorkelling at Ewens Ponds down near Mount Gambier and was amazed at the incredible plant life that was growing in the crystal clear waters of the channels connecting the ponds. The floor of the channels were carpeted with Kidney Weed - I believe one of the few places on Earth where land plants can grow in the water!! This photo was taken at the end of the channel moving in to the third pond with my Go Pro.