Caulerpa cactoides (Turner) C.Agardh
Sea cactus (Caulerpa cactoides) is one of numerous species of the seaweed genus Caulerpa, which is found on all coasts but is most diverse in southern Australia. All species have one distinctive feature in common: a horizontal stem, called a ‘stolon’, that grows across the sea floor (the genus name is Greek for ‘creeping stem’). The upright fronds of Caulerpa come in a myriad of forms. In C. cactoides, they are thick and resemble a cactus, but in other species, they can be spiny or grape-like. The pale pink coating seen on this specimen from Cape Peron is a crustose coralline alga, which does not appear to negatively impact the Caulerpa.
Sea cactus is widely distributed across southern Australia, extending north along the west coast as far as Barrow Island. It can grow in a wide range of environments, from very shallow waters to depths of 30 metres or more, on both sheltered and rough water coasts.
Photo: J. Huisman