Grateloupia filicina
Description:
This is a soft limp & slippery smooth seaweed with somewhat flattened branches
that can be red green brown or almost black. Size and shape vary greatly from
0.5-5mm wide and 2-30cm long. with either few or many branches.
Habitat:
At zero tide, rocky coastlines and shallow rocky flats.
(In: Hawai Coral Reef Network - http://www.coralreefnetwork.com/marlife/seaweeds/Cryptonemiales.htm)