By Marty Cahill Contributing Writer
Reprinted from the Panama City News Herald
Marty Cahill is a volunteer with BEST, the St. Andrew Bay Environmental Study Team. The nonprofit public-private partnership submitted this article as part of Sea Grass Awareness Month in Florida.
The benefits of sea grass may be unclear to some uninformed fishermen, but the fact is that an acre of sea grass may support as many as 40,000 fish.
Underwater sea grass may be an unwelcome impediment for an unwary shrimper, weighing down his nets and causing extra labor culling his catch. But that same acre of sea grass can support 50 million invertebrates, including shrimp, bay scallops, clams and crabs.
Shoreline sea grass may be a regulatory impediment to the developer who would prefer a white sand beach, docks and boat slips for his waterfront project. But over the previous years, that sea grass has helped prevent erosion of the land he's selling and has benefited local sport fishing, an activity that will attract his buyers.
Those who take a closer look find that a bed of sea grass is the home of a fascinating, multilayered aquatic community. And this is the best time of the year to take such a look. Springtime is when these marine beds, like our gardens and forests, wake up and burst with new life. That's what's happening right now in St. Andrew Bay.
Not many of us see the sea grasses grow into luxuriant beds, but they do. We don't see the arrival of schools of tiny young fish that thrive among the sea grass leaves, like newborn sheep or foals romping in a pasture. In fact, the teeming life of a sea grass community has led some researchers to liken the productivity, structure and diversity of these habitats to a tropical rain forest.
Fish are dependent
Of all the things that go on in a sea grass community, perhaps the most important to the people who live in or visit St. Andrew Bay is this: virtually every fish pursued by sportsmen or harvested by professionals in our bay is dependent on sea grass at some point in its lifespan. Many species are spawned in sea grass and would never survive larger predators without being shielded by the leaves and stalks.
But the link of fish to sea grass doesn't end when the hatchlings mature and leave for deeper water. Some never leave, and others return annually to feed on sea grass leaves or the organisms that flourish within the beds.
Fish are at the top of the sea grass community food chain. Next are blue crabs and stone crabs that also make their homes in sea grass at some point in their life cycle, as do pink shrimp and bay scallops. The reason? Food is abundant in the lower ranges of the food chain, with up to 50 million invertebrates to the submerged acre available to eat.
That marvelous community, ranging from the simple structure of algae to the magnificent complexity of a speckled trout, cannot exist without sea grass.
Food chain
Like terrestrial plants, sea grass manufactures its own food by photosynthesis. Therefore, sunlight is vital. Unlike terrestrial plants, sea grass does not have or need the hard, supportive trunks and stems required to grow on land. Instead, sea grass blades are supported by water and remain flexible to bend and turn with the ebb and flow of tides and currents.
Again like terrestrial plants, sea grass has a true root system that holds the plants in place and draws in nutrients and minerals from the sediment in which it grows. The leaves also provide a surface where smaller plants, called epiphytes, can attach themselves. In balanced concentrations, these smaller plants increase the productivity of the sea grass bed and enhance the food value realized by fish and other organisms that graze on the sea grass.
Water quality crucial
But like so many valuable natural resources, the broad values and varied beauties of these marine treasures are sometimes squandered. Sea grass is particularly sensitive to water quality. As noted above, it must get sunlight to manufacture its food. Sediment or algae suspended in the water can reduce or even block out that sunlight.
In normal conditions, sea grass maintains water clarity by trapping silt, clays and organic matter suspended in the water. This allows these materials to settle to the bottom where it is stabilized by the roots of the sea grass. But when the water becomes overloaded with sediment, it upsets this balance and far less sunlight reaches the leaves of the sea grass. Where water quality has deteriorated, sea grass beds have diminished and, where quality has become extremely low, the plants have actually been smothered.
Untreated stormwater runoff is a major concern in this respect. It drains off roadways and surrounding urban and agricultural areas. Stormwater may be loaded with sediment, and it often contains fertilizers, household and automotive chemicals, oils, pesticides, animal wastes and other harmful debris. Not only do these pollutants block out the vital sunlight while suspended in the water, but also, as they settle, the chemicals and nutrients in the runoff can damage the bottom and set the stage for even more severe injury to the sea grass community.
Algae grow naturally in the sea grass bed. They add substantially to the food values of the community. However, the fertilizers (nutrients) in stormwater runoff can trigger an explosion of algae growth called an algae bloom. This again blocks and sharply reduces available sunlight. Ultimately, fertilizer carried into the bay by stormwater is depleted, and the algae bloom dies and decomposes, further degrading water quality by depleting much of the oxygen dissolved in the water. When there isn't enough oxygen in the water, fish begin to die.
Boating
Prop scarring is another hazard for sea grass beds. Boating groundings in a shallow sea grass bed can cause substantial local damage, particularly if the boat propeller churns up sea grass roots. Sea grass isn't like the grass in our yards; it does not grow back quickly. When roots are damaged, it may be years before the sea grass bed can repair itself.
When viewing aerial photographs, it is shocking to see the extensive prop scarring in sea grass beds. Regardless of what the operator thought about sea grass, one wonders why he or she didn't realize the possible damage to the vessel, particularly the motor, and lift the propeller. Instead, some boaters just plow through the entire bed. An analogy would be to run a farm plow through our residential lawns!
A continuous line of scarring fragments the habitat, especially in areas where sea grass is sparse. Sea grasses that are not directly damaged by the propeller but remain in the scarred area are still at risk for erosion, which can lead to bare patches of sand in what was once a vibrant sea grass meadow.
A statewide problem
Losses of sea grass beds have been particularly widespread in the most highly developed coastal areas of Florida. For example, the Smithsonian Marine Station in Fort Pierce reports that in the 50-mile stretch of the Indian River Lagoon between NASA Causeway and Grant, Florida, sea grass coverage has decreased 70 percent in the past 50 years. In contrast, sea grass coverage in the protected zones of NASA, Merritt Island Wildlife Refuge and Canaveral National Seashore has remained unchanged over the past 50 years.
In Bay County, substantial local losses of sea grass have been documented, but they are far less severe than in other areas of the state. Maintenance and recovery of our important sea grass resources are still within reach. But it will take effective management based on sound science and strong public support.
What can you do?
If you boat, take care when you approach a sea grass bed. Do not run a boat motor over the sea grass. Pull up your motor and use a pole to ease your way out of the bed; or wade and push your boat to deeper water. Gouges from motor propellers can take four to eight years to heal.
A major communitywide effort to define and address the stormwater runoff issue is now under way. Give it your support.
Learn more about what's being done to assess and manage these issues in the St. Andrew Bay watershed area. Get involved, either on your own initiative or along with one of the volunteer organizations in the community. If you can't join the effort, support it with a contribution.
For more information or to learn how you can help, call the St. Andrew Bay Environmental Study Team at (850) 215-5590.