I don’t think anyone’s ever written a riveting story about grass, but if you were, you’d have to make sure the type of grass is worth talking about.  The spartina grass we have that’s found in our salt marsh definitely fits this bill.

Formally called sporobolus alterniflora, and known as smooth cordgrass, it’s the basis of our marine food web. While few organisms actually eat the grass while its alive, plenty of creatures need it for their continued growth and survival.

SURVIVAL OF THE FITTEST

How tough does spartina grass have it? Well, consider the obstacles it goes through for survival.

First, spartina is a freshwater plant that lives in saltwater.  When faced with an submergence of saltwater, most freshwater plants would perish, but spartina has a trick up its sleeve.  Through a process of desalination, the grass draws in saltwater through its roots, “sweats” out the salt, and retains the fresh water. If you were to look closely at a spartina stalk, you’d see salt crystals along its stem and leaves.

Because the marsh is inundated with saltwater from tidal flooding, the soil itself has very little oxygen in it. In the soil exists bacteria that actually creates its own oxygen to survive, and in the process emits a byproduct, hydrogen sulfide, that permeates the soil.  At low tide you can actually smell this rotten egg scent. 

But this hydrogen sulfide presents another challenge to spartina’s survival. High concentrations of hydrogen sulfide are highly toxic to all plants. Spartina is no different here, so why does it flourish here? Well, the plant has an ingenious solution.

Spartina has hollow air tubes that run from the top of the stalk down into its roots. The tubes draw oxygen from the air, down its stem and to the roots, which release the oxygen directly into the soil. This oxidizes the hydrogen sulfide in the soil immediately surrounding the root system, converting it to iron sulfate, which is a non-toxic sulfur. As the roots grow, this little bubble of iron sulfate enriched soil expands, protecting the plant!

SPARTINA: PROTECTOR OF THE LOW COUNTRY

So why is spartina so important? As mentioned before in a previous post, we have really, really high tides. When we have an incoming tide, the grass is almost fully submerged. This allows juvenile fin fish, shrimp larvae and small crabs to use the salt marsh as a nursery. Hiding in the spartina gives these young organisms a chance for survival from predation.  It is estimated that over 70% of all commercial seafood caught off of the coast of the United States will have spent some portion of their lives in these nurseries.

Another reason for their importance is as an erosion barrier.  The spartina lines the tidal creeks of the salt marsh and runs all the way to the tree line.  The seasonal storms we have can bring significant waves and tidal surges.  This grass is a first line of defense to absorb wave action and diffuse it before it reaches the land.

A FOOD SOURCE FOR MANY

Like all things living, spartina eventually dies, but even in death, the grass brings an abundance of life.

The dead spartina grass, called wrack, eventually makes its way out of the marsh on a high outgoing tide.  It gets washed out of the creek, out into the sound, and eventually out into the Atlantic Ocean.  While this is going on, the grass is decaying into detritus. Small microorganisms called phytoplankton will feast on the detritus. The abundance of feeding phytoplankton bring in zooplankton and small fish to feast on them, and in turn, larger organisms like fin fish, crabs, rays and dolphins eat the smaller creatures.

GRASS AS A BEACH BUILDER

And just when you think the grass couldn’t do any more, it has one last role to play. As it floats around the Atlantic, much of the wrack eventually finds itself along our beaches. Here it performs its second duty of an erosion barrier as the wrack breaks down into smaller fragments. It blends in with our fine sand, reinforcing the beaches, creating sand dunes and berms.  The dunes then become annual nesting sites of sea turtles! Loggerheads, greens and leatherbacks all make appearances every year laying thousands of eggs right here on Hilton Head.

From the salt marsh, to the waterways, to our beaches. Spartina plays an irreplaceable role in the ecology of our island.  Without it, we wouldn’t have the diversity or the beauty we often take for granted. Such a simple stalk of grass that does so much to bring life and protect it.  As far as grasses go, spartina is indeed pretty cool. While on your next dolphin tour, you can appreciate all that the spartina does for us.

Hilton Head Island is a well known place to see dolphins in the wild. But did you know we also get an influx of manta and mobula rays coming into the waterways every spring and summer?

Mobula Ray or Manta Ray?

There was a time that manta and mobula rays where considered separate families. It was only within the last 10 years that scientists had realized they shared the same genus. All mantas have now been reclassified into the mobula genus, making them the largest of the mobulas rays. The largest mobula, the giant oceanic manta, can grow up to 3600lbs and have a wingspan of 29 feet. Here on the island we can regularly see the Atlantic devil rays, with a wing span of 4 feet, and occasionally the reef manta, that can exceed 15 feet. Over the past few years several large reef manta have been spotted along the coastline. This video was taken just off of Hilton Head!

Aside from size, another way to tell the difference is mouth placement. A reef manta’s mouth opening will be at the top of its head, directly between its feelers. An Atlantic devil ray’s mouth will be slightly lower.

Intelligence of Mobula Rays

But how smart are these creatures? Mobulas have the largest brains out of all fish, with developed areas for problem solving, communication, and learning. They’ve also passed what’s known as the mirror test, meaning they have the ability to identify their own reflection and have a greater likelihood of being self aware. Studies have shown mobula can also identify individuals within a group (specific humans for example) and react accordingly.

Another example of their intelligence is shown through their hunting techniques. Different from most other rays, mobulas are filter feeders, collecting zooplankton with their cephalic feelers into their mouths as they swim along. One such hunting pattern is with a large group of rays, they will begin to furiously swim in circles, actually changing the flow of the water and trapping the plankton inside the vortex they create.  They’ll then line up, three at a time, one above the other, and enter the water vortex, mowing down the captured plankton.  Very few animals have the knowledge and ability to change their own living environment for their benefit.

Mating habits

While the water here is a bit murky, you can still see these beautiful creatures in action. As the spring waters warm up into the early summer, we get an acrobatic treat from these rays. On any given day on the sound, the mobulas will launch up and out of the water, some somersaulting, some belly flopping, others doing a semi graceful swan dive.  Why they do it is still a mystery to scientists. One theory is that the acrobatics are part of a lengthy mating ritual. 

The females release a pheromone into the water that drives the males crazy and a chase begins.  More males will join in the chase, forming a train of rays, one following the other, following the female.  This can go on for several days. Over time the competing males will lose interest until only one is left. Whether this popcorning action of jumping out of the water is the female garnering their attention or the male showing off their prowess is unknown, but it does provide for a spectacle show. 

Future of the ray

Information on mobula rays is still limited, but numbers suggest their population is going down. While their only natural predators are large sharks and killer whales, human interference plays a pivotal role in their livelihood.  Overfishing, pollution and the effect of by-catch all play a pivotal role in their decline. Locally, there had been recorded documentation of large reef mantas roaming the Port Royal Sound 200 years ago. Unfortunately, these recordings also documented the hunting of these gentle giants with harpoon simply for sport.  The rays we see today pale in size and number compared to the written testaments of the fishermen from the 18th century. Mantas are now a protected species in the United States with the hopes that the protection will give them a greater chance of survival.

Click here for our tour schedule, if you want to get an opportunity to see the mobula rays. Make sure to keep your eyes out on the water for these amazing creatures.  You can be rewarded with a magical display at any given moment.