Welcome to Marine Mondays. 🐋🐠

Today’s post features the Waratah Anemone (Actinia tenebrosa)

The Waratah Anemone is from the Phylum of Cnidaraians.

It is endemic to rocky shores and is part of a community of many different anemones living in the tidal zone. (I’ll cover some more in other posts). They are fun to spot due to their distinctive strong red to reddy-brown colouring and are a fixture of many peoples visits to our coast and a part of delightfully leisurely days/times at the beach exploring the intertidal zone.

You’ll notice that their habitat is usually in crevices, on the undersurfaces of rocks, on semi-protected and exposed rocky shores, clumping together in areas of shade, in the mid littoral zone. You may see a line of of juveniles lining the rock pool fissures which are always fun to see. The reason for their oft appearing in large groups is due to the method of reproduction, which involves the adult brooding the young (in the coelenteron, which is the area used as a stomach, an excretory organ and as a primitive vascular system), and releasing the small but fully developed offspring through it’s mouth. The offspring then attach to the nearest rock surface available.

They are visually made up of a column (the body) which is a rich red colour, a central oral disk which is lesser red in colour, and tentacles which are also bright red. Therefore a colourful feature of our rock pools. (Tentacles are tactile feelers, whilst some are chemoreceptors, where they are able to taste chemicals in the water.)

Whilst they seem to be sessile, meaning they live in the one place throughout their lives, using their basal disc to fix to a substrate, they actually are able to move and relocate by very slowly gliding.

There are two forms that we see the Waratah Anemone in. Open or closed. This refers to when the feeding tentacles are open (like a flower) or closed. It draws it’s tentacles in when it is out of the water, on low tides, to minimise it’s exposure to the air and drying out. They breathe by the method of diffusion through the thin membrane like skin which must be kept moist (by mucus).

Cnidarians are simple two celled layered organisms with jelly like support tissue called mesoglea between these layers to give them structural support and adaptive shape (hydrostatic skeleton).

Waratahs catch and immobilise their prey, of plankton and small fish by using their tentacles, each of which contains hundreds of stinging cells called nematocysts. If you very gently offer some seaweed to the tentacles you will see these tentacles move, bending into the middle of the central oral disk, where it’s mouth is located. If you were to touch these tentacles, you will feel a slightly sticky tickling feeling. That sticky sensation is when you have been harpooned by the nematocysts, but as our fingers are not their intended food source, this harpooning is of no harm to us.

As we know, life on the rocky shores can be competitive so as an adaption for survival/habitat/real estate mogul-ing, these family oriented anemone’s, have tentacles which they can use to attack a neighbour if they discern that they are not a direct relative, and are too close/are a threat to their habitat and the habitat of their direct family.

They have few predators but on a high tide are vulnerable to fish and crab predation.

Their distribution range is Vic, SA, NSW, TAS and across to southern Western Aust and NZ.

Happy Waratah Anemone day to you 

-Rebecca Hosking