Our tide pools are rich in marine life, and here’s a find that’s usually offshore a little further but has been seen in our tide pools fairly regularly.  This little heart-shaped coral is a sea pansy.  The sea pansy, Renilla reniformis looks like a little flower, but it’s really a colony of organisms in the class Anthozoa. (flower animals). It’s also called an octocoral, because most of the polyps have eight pinnate tentacles. This collection of polyps has one large bare stemlike polyp called the peduncle, which anchors it into the sand. Apparently they are more common on beaches on the edge of an inlet, because of the way the water moves. If the water gets rough, the peduncle can absorb water and become distended for a better grip in the sand. The best explanation I could find for the way the polyps work was at Wisegeek.com,

“The pansy-like body that gives the sea pansies their name is actually made up of various types of smaller, secondary polyps. Some of these secondary polyps are responsible for feeding the sea pansy. These feeding polyps extend above the sand and secrete sticky mucus to snare any tiny zooplankton and organic matter that venture nearby. Each feeding polyp sends its food to a common digestive system so the entire colony feasts or starves together.”

The little white dots are pumping polyps, which can deflate the whole pansy at low tide, when it might be exposed to air, allowing it to be covered with a fine layer of silty sand. When the tide comes in, reinflation occurs and the tentacles are extended for feeding. On Dewees Island, look for sea pansies at dead low tide in or below the tidepools south of Ancient Dunes Walk.

The sea pansy feeds on tiny particles of plants and animals in the water. The main predator is a sand-burrowing striped sea slug called Armina tigrina (which I never heard of before researching sea pansies and I am now headed out to try to find one in a tidepool!) A Miss E.B. Richardson of the Charleston Museum recorded observing striped sea slugs in 1939 at the lower reaches of Fort Moultrie, so they should be nearby.

We took this video of a sea pansy feeding in a tidepool on Thursday: you can see the eight points on the polyps that extend into the water.

Another amazing feature of sea pansies it that they emit a green bioluminescence when disturbed.  We discovered this walking on the beach by starlight at low tide… Reggie stepped near one and it flashed a green light!  (and speaking of bioluminescence, we talked about it in this blog post, and Smithsonian Magazine had a very interesting feature about it in the February 2013 edition.) The responsible chemical is luciferase, which acts with Green Florescent Protein to produce green light when the organism is disturbed.

http://www.biodiversitylibrary.org/page/8514713/#page/103/mode/1up