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.
This past summer, Florida’s Lake Okeechobee and St. Lucie Estuary became sheathed in toxic algal blooms. Do you know why these toxic algal events occurred? This month’s Salty Topics speaker series welcomes you to learn about the context of these events in a discussion presented by Dr. Karl Havens.
During early summer 2016, a bloom of the toxin-producing blue-green alga Microcystis began for form on the surface of Lake Okeechobee. By July, it covered nearly 45% of the surface of the lake with a fluorescent green surface scum. The bloom was fueled by high levels of nutrients (nitrogen and phosphorus) in the lake water that come from agricultural runoff, and by warmer than average water temperature and good underwater light conditions that were favorable for rapid growth. At the same time that this bloom was happening in the lake, the US Army Corps of Engineers was releasing large quantities of water from the lake in order to lower water levels in preparation for hurricane season. They are required to do this by a federally-authorized ‘lake regulation schedule.’ The flood control releases carried nutrients and toxic algae downstream to the St. Lucie Estuary, where massive blooms also developed and included another toxic species called Anabaena. As of late August, the blooms persisted and the ecological, human health and economic impacts have yet to be determined. A perfect storm created this event, and to fully understand it one must have some context about the regional flood control system and about sources of nutrients – topics to be discussed as part of this talk.
Karl Havens is a Professor at the University of Florida and Director of Florida Sea Grant, which is a NOAA-funded program that is a partnership between the Department of Congress, the State University System of Florida and Florida coastal communities. The mission of the program is to support research, education and outreach to preserve coastal resources and economies. Dr. Havens has been studying lakes for over 30 years and has published over 160 journal articles, three books and numerous book chapters dealing with harmful algae and other topics related to human impacts on lake ecosystems.
If you’ve spent any time fishing along shore or strolling in our parks along the shoreline of Charlotte Harbor, you’ve probably noticed all the green algae attached to the rocks and other intertidal structure. I walked along the shoreline at Bayshore Live Oak Park and noticed two species of filamentous green algae. One species was closer to the water than the other in what biologists refer to as resource partitioning. I suspect that the one closer to shore is probably better adapted to being periodically exposed at low tide. The other is probably better at competing in deeper water.
Closest to shore I saw Enteromorpha flexuosa. If it has a common name I don’t know what it is. Enteromorpha means “intestine-shape,” and this algae resembles hollow tubes much like intestines. Enteromorpha is light green, unbranched, and only about four to five inches in length, often shorter. It grows in clumps or tufts at or near the low-tide line and is often found on rocks, mangrove roots, or other woody debris. This species of algae has a wide salinity range and can be found in almost any shallow-water brackish or marine environment.