The Great Coraline Algae Die-Off

Coraline algae  Hydrolithon and Sporolithon, Kahalu'u 2012

   About ten days ago the coraline algae died.  The rocks along the beach here in Kailua, previously pink and brown, turned chalky white virtually overnight.  I assumed the obvious...that the flat waters of the Creepy Calm had left the algae high and dry and it had died as a consequence.  Just to make sure that there wasn't a toxic spill or some other factor, I wrote to one of my scientific correspondents, Marta deMaintenon of the Marine Biology department at the University of Hawaii at Hilo.  She reminded me that she was a mollusc girl and referred me to an algal specialist, Karla McDermid.    Now I've got the official skinny on the dead crustose coraline algae and, with thanks to Dr. McDermid,  I'm going to pass it on to you.
    Crustose colraline algae are single celled plants that lay down calcium carbonate that coat rocks and shells, and also help bind together hard coral reefs.  The algal cells have chlrophyll, carotenoids and phocobilin pigments that produce the red and purple colors.  In the absence of water the cells die.  They fall victim to both  thermal damage and water loss.  The dead cells, along with the residual calcium carbonate, appear white. 

Other algae species are also affected.  Kona Makai 2012

    I was more familiar with the bleaching of hard corals.  Hard coral is the structure produced by small animals closely related to sea anemones and jellyfish, ie cnidarians.  The coral polyps incorporate algae cells, called zoanthellae, which give the coral its color.  In addition to providing some tone to the reef, these algal cells also produce sugars and oxygen which nourish the polyp.  They also assist in the secretion of calcium carbonate.  When polyps are stressed they expel the zooanthellae, hence losing their color (bleaching).   In the process, they lose all the good things those algae cells provided.  If the coral polyp does not soon re-incorporate the symbiotic algae cells, it dies and the the reef, the product of ages, collapses.  There has been lots of research on coral bleaching.  Heat, UV light and pollution of various kinds have been implicated as causative factors.  Whatever the cause, its a worldwide problem of substantial concern.

Deep in the Kona Makai blowhole the algae is still pink.

   Lucky for us and our rocks, not all the coraline algae cells on the Kona coast may be dead.  Some may have been shielded from the heat and dessication and lie dormant.  When the Creepy Calm departs (just this week we have seen some increased surf) those algae may grow again.  Additionally new algal cells will recolonize our rocks when conditions permit and soon those skeletal white patches will bloom with color.
  
So think pink and stay as wet as you can,
jeff