Sea Point Tidal Pools

Yesterday, I spent a lot of time exploring.  In addition to shopping for dried fruit and spices for Antarctica, I went to Sea Point and spent an hour exploring tidal pools.  There are so many organisms that I don't know anything about!

Highrise apartments and hotels with the backdrop of mountains frame one side of the beach, with metamorphosed sandstones framing the ocean side.

Large swells lift kelp and are broken by the rocks at low tide.  The rocks hold the water for the pools.

The orange is a sponge, the same color as chert veins in the sandstone.  What are the deep red slime domes?

The large limpets, like the one above which is about 7 cm in diameter, host many other organisms, in this case mini green starfish.

Other, smaller limpets are iridescent, but other small ones host sea weed.

The purple ridge on this organism overlies a muscle that lifts the gas-filled bag of its body up out of the water, or relaxes to let it lie flat.  It has scalloped tentacles, in mixed dark blue and turquoise.  It must be related to jellyfish.  The dried ones on the beach pop when you step on them.  

Addition: Neil gave me their name (see comments): Physalia physalis or Portuguese man-of-war or bluebottle.  They are colonial hydrozoan, which means that each "organism" is actually made up of many individuals that take on special roles in the colony.  This is a form of "multicellularity" that we don't often consider.  How do the individuals "decide" what role to play in the "organism"?  It must be communicated through chemical signals, but without a controller.  Their bodies strike me as a wonderful emergent pattern!

The base of this organism looks like a shell, which supports the translucent "sail".  However, it might be just organics.  Most of these mysterious organisms (mysterious because I'm ignorant as to what they are) were upright on rocks, like this one.  A few were floating on the surface of the pools.  How to they reorient themselves after the waves? 

Addition:  Neil gave me the name (see comments): Velella Velella or By-The-Wind Sailors.  They are also colonial hydrozoans, with a different emergent pattern.  Life is amazing. 




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