Seaweeds upon seaweeds

The beaches along Wellington's south coast are often strewn with seaweed, often literally stacks of seaweed, washed up after a southerly storm.  A few days ago I came across this pretty sight on the sand at Lyall Bay, the colourful cluster of a small seaweed on the holdfast of a bigger brown one.

What were they?  I had to consult an expert for their names - thanks Wendy! and any mistakes are mine.  The leathery brown seaweed is Carpophyllum maschalocarpum.  Also known as the flapjack it is a common seaweed here, living on rocks in the low tide zone and coping with moderately exposed conditions.  Covering its holdfast are the glossy little beads of a green alga, Caulerpa geminata.  Unsurprisingly the pinky red ball structure is not a seaweed, and could be a sponge or a compound ascidian - closer inspection would be required.  Surprisingly, the pinkish tinge on many of the pretty green beads is caused by another kind of seaweed - an epiphytic nongeniculate coralline alga making a very fine pink coating on the beads. 

Closer up, another pink nongeniculate coralline alga is in view - this one a thick crust.  "Nongeniculate" means the algae are not articulated or branched, but are flat growths ranging from a few micrometres to several centimetres thick.  Crusty patches of such coralline algae on rocks in the intertidal zone can look just like patches of pink paint rather than living things.  Look for the blotches of pink paint next time you are exploring the rocky shore - when I started to look, there they were! 

Blades, beads, crusts, coatings - seaweeds come in a great range of sizes and forms.  And much of this we often don't notice or give our attention.  I was asked what I was photographing several times while getting these pictures and got a puzzled reponse when I answered "these interesting seaweeds."

And they can be edible too!  I haven't tried them but apparently the little green beads taste quite a lot like cucumber with a slightly peppery quality, and close relatives of this species are sold in markets across Asia and Pacific as a sea vegetable - either eaten fresh or in coconut milk.  Yum.