THE OLIVE TINGE of seawater off Hilton Head Island may surprise first-time visitors here. Why isn’t the water crystal-clear, like Waikiki Beach or the Bahamas, for instance? There is a perfectly natural reason for this condition, and it bodes well for the ecological health of surrounding waters.
Gifts from the Ocean Garden
In the Atlantichttp://geography.about.com/library/cia/blcatlantic.htm Ocean, as in your garden, summertime is the growing season. When water near the shore tops 85 degrees (July-August), what flourish most in the shoals are diatoms. These are microscopic, one celled, plants known as phytoplankton (translation: “floating plants”). Diatoms are harmless to people, and in fact are significantly beneficial in the ocean ecosystem. When conditions are right, diatoms and their kin turn the water pale, greenish-gold.
Diatoms are a main ingredient in the Nature Soup of micro-plants and animals in the ocean shoals. These are consumed by filter feeding shrimp snails, clams, crabs and fish in the sea, on the seafloor, and even in the beach sand. Watch for holes and tubes on the lower beach: there is a live, plankton-gobbling critter living in each! The gulls, terns, brown pelicans, splashing schools of fish, and bottlenose dolphins are all out there because the colorful ocean supports the food web they need to survive.
The Salt Marsh Plays a Role
The brownish tint in the ocean is caused by detritus—suspended plants particles that tides carry from salt marsh on the lee side of the island. This fecund wetland generates 10 tons of detritus (Latin for “wear away”) per acre every year. So, some of this organic bouillabaisse is going to make its way to the beach, courtesy of strong currents and 6-9 foot tides.
The Blue Desert
Aquamarine tropical seas are certainly beautiful to view. You can even see your feet when you wade. Snorkeling is superb. But the clear blue water is quite empty of ocean life. Most biological activity is concentrated on reefs. Those postcard-perfect Bahamian waters are caused by the scattering of light among water molecules unfettered by diatoms or organic matter. Truth is, the tropical sea is a water desert compared to South Carolina’s lively, colorful ocean.