Secrets of Seagrass
ecologic and economic engine

by Kris Thoemke

THERE IS A GRASS GROWING in Florida that is always green and never needs to be watered. You do not have to mow or fertilize it. If you’re looking out your window at your lawn wondering how much something like this would cost – well, it might cost up to $20,000 per acre. Don’t worry though, there is no place to buy it and even if you could, it will never grow in your yard because you are missing two key requirements for this grass. It grows underwater and requires the saltwater to survive.

This grass goes by the name ‘seagrass’ and if you don’t spend much time in places like Estero Bay and Charlotte Harbor, you may not be familiar with seagrass or realize the economic value of these unique plants.

the ecology

Seagrass is a generic term for species of flowering plants that re-adapted to living underwater. They are flowering plants with leaves (referred to as blades because they resemble blades of grass), roots and, like all plants, can make their own food via the process of photosynthesis.

The three most common species in southwest Florida go by the names of shoal grass, manatee grass and turtle grass. Shoal grass is, as its name implies, typically found in shallow water sometimes growing in areas where it is exposed during low tide. The blades are narrow, often only a few millimeters wide. Turtle grass blades are about a half inch wide and the ends of the blades are rounded. Manatee grass is easy to identify because the blades are cylindrical.

Seagrasses are common in shallow waters in Florida Bay and in most bays and lagoons along the Gulf of Mexico and Atlantic coastlines. In southwest Florida, seagrass is common throughout Charlotte Harbor, Estero Bay and similar areas.

Most people don’t understand and appreciate the importance of seagrasses to the local economy. It’s no secret that tourism is big business in Southwest Florida and contributes millions of dollars to the region’s economy. What may surprise you is that the presence of seagrass contributes greatly to the reasons tourists visit this area and how that impacts the economy.

Any angler who fishes in the ‘backwaters’ knows that seagrass beds, as large areas of seagrass are referred to, are a good place to find snook, sea trout, and other species of fish. These fish prowl the seagrass beds for a very good reason. It’s a great place to find their next meal.

Areas of seagrass, with thousands to millions of blades, form a complex three dimensional maze that offers countless places for small fish and shellfish to hide and avoid predators. It‘s also where the small critters find the food they need.

the economics

The food and shelter provided by seagrasses is one of the reasons why these areas are referred to as ‘nursery’ areas for at least 70% of recreationally and commercially harvested fish and shellfish. For these species, seagrasses are home for their young. Without seagrass there wouldn’t be many of the fish targeted by anglers.

Just how valuable is seagrass? A single acre of seagrass may support as many as 40,000 fish and 50 million small invertebrates. The recreational fishing industry, which generates millions of dollars each year, would not exist if were not for the benefits provided by seagrasses. A Nature Conservancy study released last year reported that one acre of seagrass could be worth up to $8,000 of fish in one year – year after year.

Seagrasses also contribute to the eco-tourism industry. They are an important food source for sea turtles and the endangered West Indian manatee. Manatees are primarily vegetarians and if you hang around areas where seagrasses are prevalent, there is a good chance you will see one or more manatees grabbing one of its many daily meals.

Studies have estimated the value of seagrasses to the economy ranging from about $7,500 to over $20,000 per acre. A 25-acre seagrass bed has an annual economic value of $200.000 to $500,000 per year. Over time, the value reaches billions of dollars. Seagrasses are crucial to the economy of Southwest Florida.

It’s not just seagrasses that make this system so productive and important. If you look carefully, most seagrass blades appear to be coated with a layer of fuzzy material. This coating consists of a variety of small organisms such as algae, sponges, barnacles, crustaceans, and worms. This community of organisms matter because they are a food source for the small organisms fed on by small fish that become food for larger and larger fish.

Think of these relationships like this: There is no such thing as a free lunch. A larger fish is always waiting to make something smaller its next meal. And at the top of this heap are the anglers that harvest the fish.

the future

Despite their role as economic engines, seagrasses have an uncertain future. Recent statewide estimates found about 2.2 million acres of seagrass. While that is an impressive sounding number, consider that in 1950 there were 5 million acres of seagrass. This decline arises from both natural and human-related impacts and the latter is of most concern.

Any event that contributes to a decrease in water clarity can have an adverse impact on seagrasses. Storm runoff containing suspended sediments can reduce water clarity as can discharge of excessive nutrients from sewage treatment plants and indirect sources such as farm field and lawns. Excessive nutrients create a condition where the small, single celled phytoplankton multiply at an accelerated rate causing decreasing water clarity, which decreases the amount of sunlight reaching the seagrasses. Seagrasses, like any plant deprived of light, may eventually die.

Another problem in many places in southwest Florida results from boats that travel in the shallow waters where seagrasses are present. When a boat’s motor is on or near the bottom and boaters mash down the throttle to get on plane and skim across the shallow flats, the prop can act like a dredge and slice through a seagrass bed leaving a distinctive scar in the seagrass. This trench represents an area where the seagrass blades and the underground rhizomes (roots) are chopped and destroyed.

The good news is that prop-scar impacted areas of seagrass can re-grow. Prop scars may require several years to recover, but larger areas that are lost may never recover without help. Seagrass restoration is a developing industry that typically involves transplanting seagrass into a denuded area and then monitoring the recovery for several years. Seagrasses are finicky and not every restoration project works. Moreover, at a cost of $100,000 to $1,000,000 per acre, it is a costly proposition with no guarantee of success.

There is much activity going on below the surface of the shallow waters of Southwest Florida bays. You won’t hear it and you would be hard-pressed to see much of what is happening. But without seagrasses and the benefits derived from them, this would be a far less attractive place to live and a far less inviting place for people to visit.

Seagrasses, the silent economic engine. Who would have imagined? •

March-April 2015

One acre of seagrass
could be worth
up to $8,000 of fish
in one year