Found in an inter-tidal channel near Pretty Beach, Murramarang National Park. Division Phaeophyta, Family Dictyotaceae, Genus Dictyota (thanks to J. Huisman). Species uncertain.
Thanks very much for your comment Liz. John H. did not say at the time why he wasn't comfortable with calling this Dictyota dichotoma, so I've just emailed him. It's possibly due to discussion like this in algaebase.org: