March was National Seagrass Awareness Month. And although it’s now April, one could argue that we should not ONLY be aware of seagrass one month out of the year. Seagrass is important and deserves our attention throughout the year!
Seagrass are a relatively small group of flowering plants that have adapted to survive and reproduce in a marine environment. In fact, they alone are the only flowering plant that can live their entire lives completely in seawater.
Worldwide there are about 50 species of seagrass. Seven seagrass species occur in Florida, and all but one of those can be found in Charlotte Harbor. The three you are most likely to see are Turtle grass, the one with the wide flat blade (leaf), Manatee grass, a long skinny tubular grass found closer to the passes where the water is nice and salty, and Shoal grass, this one’s very fine, with thin flat blades; sometimes you see it exposed at low tides.
Each seagrass species has its own personality, things it likes, things it can tolerate. Shoal grass for instance, has a wide salinity range and can grow in low light conditions. Manatee grass however, has a narrow salinity range and needs high light conditions. And, Turtle grass has a lot of surface area on its blades, making it a favorite place for algae, tube worms, and barnacles to attach.
Seagrass abundance in Charlotte Harbor has been pretty stable since the late-80s when the Southwest Florida Water Management District (SWFWMD) began flying aerial surveys in order to calculate seagrass acreage. Our acreage has gone up and down in response to wet years and dry years but has consistently been between 17,000 acres and just over 19,000 acres; although the last survey brought us over 20,000 acres (2016). The Charlotte Harbor surveys do not include Lemon Bay, which gets its own survey and is also seeing a slight uptick in acreage.
Stable or upward trends are good, but do not mean our seagrass is where it needs to be. Let’s face it Charlotte Harbor & Lemon Bay’s history goes back a bit further than 1988! Ok, a whole lot further back, but the best we can do is the 1950s. This is when the earliest aerial surveys were taken that have the resolution needed to map seagrass acreage. Some of the acreage from those earlier aerials are lost for good; think ICW, other channels, canals, etc., but even removing those acres, in some areas we still had more seagrass then, than we do now. On the flip side however, there are also areas of the harbor that have more acreage today than they did in the 50s.
How do we gain acreage where it’s needed? The key here is nutrients (nitrogen and phosphorus). Nutrients are good in the right amounts. In fact, in a natural system there are just enough nutrients, but then there’s us, adding more. Excess nutrients cause algae to bloom, both microscopic algae and macroalgae (think drift algae). When that happens the water becomes murkier. Guess what? Algae thrives in high nutrient conditions with low light levels. Seagrass on the other hand requires low nutrients and high light levels.
To address excess nutrients entering our estuary, Charlotte County and the City of Punta Gorda both have fertilizer ordinances, and Charlotte County is actively working to expand its sewer system throughout the County. Other projects, such as oyster restoration, the development of living shorelines, and enhanced stormwater treatment programs are also being implemented to reduce the level of excess nutrients that enter our estuary.
If we think of seagrass acreage as the big picture, we might also want to delve into some finer details as we explore measures of seagrass health. For instance, how thick are the seagrass beds? This is something aerial photos can’t really get to, but on the ground surveys can. Since 1999, the Charlotte Harbor Aquatic Preserves have conducted such in water surveys of seagrass in Charlotte Harbor. The stormy years of 2004 and 2005 really impacted our seagrass and it showed up in these surveys. Seagrass abundance (that thickness) rose from 2006 to 2010 and has been pretty stable since then.
A trend that has been not so favorable is the amount of seagrass scarring that has occurred over time in the estuary. Only two seagrass scarring surveys have been done for Charlotte Harbor (including Lemon Bay all the way down to Estero Bay), one in 1993 and the other in 2003. The results showed a 10,000 acre increase in scarring between years. In Charlotte County 58% of our seagrass was scarred in 2003!
Why is this bad? Well bare substrates (natural or scarred) support a lower number of animals and few species than adjacent areas with seagrass. And, some studies have shown that predation is greater at the edges of seagrass as opposed to other seagrass locations. So more edges due to scarring could potentially impact the amount of forage fish over time. Did you know? Destruction of seagrass in an aquatic preserve (which Charlotte Harbor is) carries a penalty of up to $1,000.
Let’s all celebrate seagrass year round by being stewards of this beautiful resource on the water and on the land.