I presume this is some sort of staining fungus (species unknown) degrading driftwood on the beach. These pioneer saprobes (saprotrophic=feed on dead material) are an early part of the wood decay process. The green colored stain comes from the fungus’ melanin deposition. While these fungi are not capable of degrading complex polymers like lignin and cellulose, they can consume easily accessible sugars in the dead plant cells. These organisms grow and reproduce quickly, however pioneer saprobes are eventually wiped out by fungal species that secrete antibiotics later in the decomposition process. Let me know if you recognize this beautiful pattern of decay.
*Update: a mycologist has informed me that this could very well be a pigmented fungus, but it could also be algae remnants. This gives me an excuse to go back to the coast so I can determine if my hypothesis is correct :)

















