EPOW - Ecology Picture of the Week

The Alga That Thinks It's A Coral

Articulated Coralline Algae (Calliarthron sp.)
Division Rhodophyta, Class Florideophyceae, Order Corallinales, Family Corallinaceae
Bodega Bay, California, USA

Explanation:  What looks like some alien vertebrae is actually a closeup of a common algae found in the lower intertidal to subtidal marine realms of the world.  This is an "articulated coralline algae," belong to the group of species called "red algae" (Rhodophyta).  To most people, it is just seaweed found strewn on rocky beaches, but there is so much more to this denizen of the sea.

Why does this "lower" life form grow in neatly-fitted segments?  The answer is in the turbulence of its marine environment.  The segments join together to allow the entire body to sway and bend in the always-moving water, as these species often occur in the shallows of the ocean floor where currents and waves and tides are a constant force.  It also commonly occurs in relatively shallow water, as it needs access to sunlight because it photosynthesizes energy.  

But its articulated structure is most interesting, growing with bifurcating (branching) arms much like some corals.  The segments are made of durable and dense calcium carbonate, so to sway in the marine winds it needs articulation and bends at the joints.  When it breaks, however, it tends to snap at the holdfast it uses to attach to rocks and other substrates (including other plants) rather than breaking at any of the segments.

This entire thallus of an articulated coralline red alga washed up on the rocky beach of the coast of central California.

Note its fan-like structure and the other marine organisms attached to it.  

Articulated coralline algae reproduce asexually with sporophytes, and sexually from male and female gametophytes, and undergo a three-stage life history.  This is not a simple life form!

The calcified segments function like vertebrae and most are
covered by cuticles.  Seen in this photo and especially in the main photo
above are nipple-like protrusions called uniporate conceptacles
in which reproduction takes place.  These conceptacles can
produce male sperm, female eggs, or asexual sporophytes.
 

 

This articualted corraline red algae
is likely Lithothrix sp.,
although species identification is difficult
and depends in part on the
branching pattern.

 

 

   

Acknowledgment:
     My thanks to marine biologist Dr. Susan Williams of University of California's Bodega Marine Laboratory for identification.