Seagrasses - An Important Natural Community

Common Household Items
Become Seagrass Metaphors
by Tim Marshall , OPS Ranger

Seagrasses Metaphors:
Seagrasses are “air conditioners”
Seagrasses are “coffee filters”
Seagrasses are “Rolaids”
Seagrasses are “carpeting”
Seagrasses are “pillows”
Seagrasses are “cereal”
Seagrasses are “nurseries”

How So?
Seagrasses are flowering plants that live underwater. Seagrasses serve as underwater “air conditioners” because, like land plants, seagrasses produce fresh oxygen and help to remove particulate matter.

The depth at which seagrasses are found is limited by water clarity because they require light. Although seagrasses occur throughout many coastal areas of Florida, locally, they are most abundant in the Tampa Bay, and on the gulf coast they are most abundant from Tarpon Springs northward to Apalachee Bay. Seagrasses occur in protected bays and lagoons and also in places along the continental shelf in the Gulf of Mexico.

In 2003, over 2 million estimated acres of seagrasses were determined to be playing an important role as natural resources that perform many significant functions:
1) Seagrasses are coffee filters,
they help maintain water clarity by trapping fine sediments and particles with their leaves; like Rolaids, they neutralize harmful chemicals.
2) Seagrasses are carpeting, they stabilize the bottom with their roots and rhizomes in much the same way that land grasses retard soil erosion.
3) Seagrasses are pillows, in that they provide safe resting places and needed habitat for many fishes, crustaceans, and shellfish.
4) Seagrasses are morning cereal. The seagrasses and the organisms that grow on them are food for many marine animals.
5) Seagrasses are nurseries and incubators, they are nursery areas for much of Florida’s recreationally and commercially important marine life.

Your daily encounters with common household items should now serve as ready reminder of the daily duties of our seagrass beds, as they serve to benefit us all.

Lets look a little more closely. Seagrass leaves provide excellent protection for young marine animals from larger open-water predators. Some animals, such as manatees eat seagrass blades. Other animals derive nutrition from eating algae and small animals that colonize seagrass leaves. These colonizing organisms provide an additional link in the marine food chain.

Our Seagrass Species
Although approximately 52 species of marine seagrasses exist worldwide, only seven species are found in Florida waters. Four of these are widespread in Florida and extend beyond its borders. Of these, just three are commonly found in the waters surrounding Honeymoon and Caladesi Island State Parks.

Turtle grass (Thalassia testudinum) is the largest and most robust seagrass in Florida. Its ribbon like leaves are about 1/2 inch thick and up to 14 inches long. It grows in waters up to an extreme of 82.5 feet deep, and withstands salinities as low as 20 ppt. This beneficial plant actually prefers shallower water up to 33 feet, and does best in a salinity range between 25 to 40 ppt. Turtle grass is the dominant seagrass in most estuaries in Florida.

Manatee grass (Syringodium filiforme) is the second most abundant seagrass in Florida. It is readily identified by observing its unique cylindrical leaves. The leaves vary greatly in length, but can grow up to 20 inches long in some areas. Manatee Grass can withstand salinities as low as 20 ppt. It is commonly mixed with other seagrasses, or sometimes found in small patches by itself. On rare occasion, it can be found as the sole species in large meadows.

Shoal Grass (Halodule wrightii) is extremely important as a colonizer of disturbed areas where Turtle Grass and Manatee Grass cannot grow, or where scarring or other disturbances take place. It is often found in waters otherwise too shallow or too deep for other grasses to grow. Shoal grass can withstand the widest variance in water temperature, depth, and salinity factors.

Seagrass Awareness
Seagrasses stabilize the bottom sediments and help to absorb excess nutrients from land run-off. Damaging seagrass beds leads to continually re-suspended bottom sediments and nutrients that damage the quality of our waters. Seagrass communities support hundreds of species of fish at various stages of their lives. Without healthy seagrass beds, these fish populations are compromised -- as well as negatively impacting commercial and recreational fishing, further stressing our coral reefs, and affecting the food chain tto a degree as to even impact our shore birds.

There is scarring on most every seagrass bed. Damaging seagrass with boat propellers fragments the grass bed and severely restricts the movement of marine wildlife in needed habitat, creating barren areas where fish and others once flourished.

Our Impact on Seagrasses
A moment’s carelessness can quickly impair this precious resource -- a propeller scar cut into seagrass today can be around in five years or longer. Running aground costs millions of dollars each year to boaters, resulting in towing fees, propeller replacement, engine repair, and legal fines.

The shallow waters of Clearwater Harbor, St. Joseph Sound and our other area bays and estuaries pose a particular challenge - even to the most experienced boaters. Study your charts Read the waters. Know your depth and draft. Losing our seagrass means more than a few blades of grass.