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Excerpts from Jim Conrad's
Naturalist Newsletter
from the January 4, 2015 Newsletter issued from Río Lagartos, on the Yucatan Peninsula's northern coast (~N21.60°, ~W88.16°), Yucatán state, MÉXICO
SOFT CORAL/ OCTOCORAL
It took about a month of sporadic but almost daily sleuthing on the Internet before I halfway figured out the identity of the prettily arrayed item shown above. This washed up on a sandy beach on the Gulf of Mexico side of the narrow finger of land across the estuary from Río Lagartos. A close-up of the thing's bumps and curiously sinewy stem -- with lines on my fingers providing scale for the stems' size -- appears below:
The delay in identifying this organism came from my assuming that it was an alga. In retrospect, its texture should have cued me to its non-vegetable origin, for it was rubbery like gristle in flesh or a dried-up earthworm, not brittle, crumbly, succulent or woody like most plant tissue. Eventually I had to review the whole spectrum of Life on Earth to see if the strange being might fit into a category that until now I'd just overlooked, or forgotten about. That turned out to be the case.
For,on the Evolutionary Tree of Life, the low branch known as the Animal Kingdom branches next into phyla, and one of those phyla is the Cnidaria, which embraces over 10,000 aquatic, mostly marine species, including jellyfish, sponges, sea anemones, corals, and certain life forms I'd been blind to until now. A feature of most cnidarians is that during their life cycle they alternate between two very different forms -- swimming, sexually active medusas such as jellyfish, and "rooted" or "sessile" polyps such as sea anemones.
Moreover, even among cnidarian phyla I'd heard of, there were branches that until now I hadn't noticed. A lot of corals don't look at all like what I thought all corals had to look like.
Digging deeper into the coral's Class of Anthozoa, I found the Subclass Octocorallia, the "octo-" part of the name referring to the eight-fold symmetry of their polyp stage. Octocorallia include such creatures as sea pens, gorgonians (sea fans and sea whips), blue coral and soft corals.
Soft corals were new to me. Soft corals belong to that subdivision of the Subclass Octocorallia known as the Order Alcyonacea. Pictures of soft corals on the Internet show creatures looking like the thing in our photograph... Soft corals, unlike the hard corals forming coral reefs, do not produce rock-hard skeletons consisting of calcium carbonate. They're soft, like our washed-up item on the beach.
Soft corals -- the Order Alcyonacea -- are not well represented on the Internet, so identifying them isn't as easy as getting the name of a fish or sponge. However, luckily, there was a 2010 paper by Devictor & Morton entitled "Identification guide to the shallow water (0-200m) octocorals of the South Atlantic Bight." The South Atlantic Bight study area was defined as that part of the US Atlantic coast between Cape Hatteras, North Carolina and Cape Canaveral, Florida.
Using that guide, with fair confidence I identified our washed-up octocoral as SCLERACIS GUADALUPENSIS, known to commonly turn up from North Carolina on the US Atlantic coast south through the Gulf of Mexico and the Caribbean, and off the coast of Brazil.
Referring back to our pictures, the entire organism sprawling on the sand can be called a soft coral or, more technically, an octocoral colony. Soft corals occur in branching, encrusting, whiplike, feather-like, or fleshy forms. Ours is a brancher. The above paper states that "The type and degree of branching (or lack thereof) may easily distinguish some species." Ours branches in a "dichotomous" manner. The warty bumps along its stems are referred to as calyces, and the calyces arise opposite one another on their stems, though in an overall spiraling manner. Embedded in each calyx is a tiny polyp whose eight, stinging-cell-equipped tentacles grab onto plankton in water circulating around them.
Soft corals provide habitat for fish, snails, algae and a diversity of other marine species.
All corals, unlike other cnidarians, lack a medusa stage in their development. They release sperm and eggs into the water that result in tiny, specialized larvae with cilia called "planulae," which crawl around and eventually attach themselves to some substrate on which they develop into corals. The University of Louisiana at Lafayette hosts a comprehensive page dealing with octocoral reproduction at http://www.ucs.louisiana.edu/~scf4101/Bambooweb/repro_AS.html.
What a magnificent thing to be introduced to a whole new form of life I'd not known about before, simply lying artistically arrayed on wet, fishy-smelling, Gulf-coast sand!