SEAGRASS/ SHOAL GRASS

"Seagrass" is a general term commonly applied to long, slender aquatic plants rooted on the seafloor. Not far offshore here the seafloor is solidly mantled with seagrass. Up the beach about a mile dark patches of seagrass occur close to shore, then the water turns dark where pure seagrass begins, as shown below:

At low tide patches of seagrass close to shore may rise above all but the larger waves. When the water is lowest, often beautiful tropical fish shelter at the mats' edges and make brief forays across the shallow water above the mats. There are hours when thin sheets of clear water flow over the dark mats and the seagrass first points this way, then that way, depending on water flow direction, as below:

Best I can figure out, the fuzzy, greenish stuff at the bases of some of those slender stems is alga growing on the seagrass, while the whiteness covering the seagrass stems' top parts, mostly to the left, is carbonate gunk that chips off as the "grass" moves. Breaks in the pale gunk give the plant stems a segmented look, but the stems aren't segmented.

Based on technical literature and pictures on the Internet, I'm guessing, that the "grass" here is Shoal Grass, HALODULE WRIGHTII, not a grass at all but rather a member of the monocot Manateegrass Family, the Cymodoceaceae.

Ecologically the important thing about Shoal Grass is that its roots penetrate an average of four inches into the substrate, thus stabilize offshore sand. Some landowners along this beach, wanting the turquoise water you see above naked, submerged, white sand, send workers out with machetes to uproot the Shoal Grass. They are encouraging the sea to wash away their beaches. The irregularly shaped, dark mats in the first picture stand about two feet above the naked sand surrounding them.

Right up the beach from here, for years a resort has systematically removed seagrass from before its beach. You can see a picture of the way that looks now below:

Ten years ago, I'm told, nearly all of the water you see in that picture was sandy beach with large Coconut Palms growing on it. It ran almost parallel with the rocky point seen at the distance. Beach erosion began immediately after removal of the seagrass began. The resulting little bay was already in place when Hurricane Dean came through last year.

Not only Shoal Grass but also the Turtle Grass, Thalassia testudinum, I told you about some Newsletters ago, host nitrogen-fixing anaerobic microbes on their roots and rhizomes, thus, like members of the Bean Family on dry land, in the sea these plants "fertilize" other aquatic plants in the area with usable nitrogen.