[dropcap]T[/dropcap]here was a time in the recent history of the Indian River Lagoon (IRL) on the east coast of Florida that the word algae was used in reference to the macroalgae that populate the Lagoon – a diverse group of alga species that you can see with your naked eye, otherwise known as seaweeds. Growing in and around the plants and animals of the IRL, their spores germinate in the bottom sediments or on hard surfaces and are often ripped free by the agitated action of wind and waves to become drift algae. Entangled and tumbling through the shallows as colorful mini-communities, they continue to provide ecosystem benefits until the end of their life cycle. These days when talk turns to algae in the IRL it is with distain and concern because of a major shift from macroalgae to microalgae. What are these living things that are neither plant nor animal but are wreaking havoc in our beautiful Indian River Lagoon?
The ability to use the sun’s energy to photosynthesize food and oxygen out of nutrients is found in three Kingdoms – plants (Plantae), algae (Protista) and cyanobacteria (Monera). All three have been inventoried in the Lagoon in the past but with significantly different abundance ratios. And just as invasive plants cause imbalance of native plants, there are both good and bad algae and cyanobacteria.
Protists must live in water. These algae lack transport cells so immersion in water enables whatever nutrients are in the mix to absorb directly into their surface cells and more nutrients equate to more growth. They have advanced cell structures but are generally single-celled or rarely thicker than a few cells. Plankton or unicellular algae, in moderation are an important food source for juveniles at the bottom of the food web. The presence of plankton in coastal water, usually seasonal, is a known cause of turbidity but ordinarily it would not be noticeable except for the lack of crystal clarity. It is becoming an issue however as we continue to add more nutrients to our watersheds fueling their blooms.
Multicellular algae, better known as drift algae or seaweed, are also considered protists. They however do little to make the water turbid but they will diminish light penetration if excess nutrients cause them to grow out of balance in the seagrass community, or if they drift and effectively cover photosynthesizing seagrasses. Powered by wind, the drift algae eventually shades itself enough to die-off and drops to deeper water to decompose. In early 2010, when we lost an entire crop of macroalgae in the northern IRL, likely due in part to a prolonged cold snap, we began to understand that it serves not only as a shelter for organisms but as an important nutrient “sponge” during winter, for example, when other users are less productive because of the angle of the sun. Without a significant recovery of the macroalgae community from that season, nutrients shifted to fuel plankton blooms and what followed was an ecological disaster. In addition to a tell-tale water color change the blooms shaded the seagrasses with no relief for months, resulting in their death.
True plants have complex transport systems that move nutrients and water within the plant. These are the most familiar producers and they are found in and along the shoreline of the IRL – seagrasses, saltmarsh grasses and mangroves. They are beneficial to the ecosystem mostly because they have a consistent nutrient demand resulting in recycled decaying organic matter that slowly releases nutrients as they die and degrade, all this while providing shelter for many species. Seagrasses, as submerged plants, are in big trouble. They depend on sunlight for photosynthesis to penetrate to the bottom of the water column where they are attached and unfortunately where harmful blooms effectively block the light. The IRL has lost tens of thousands of acres of highly productive seagrasses since 2010.
Cyanobacteria, otherwise known as blue-green algae, are bacteria with chloroplasts. They have primitive cellular structures identical to bacteria but have the ability to photosynthesize like plankton, a powerful tool. When nutrients are available and cyanobacteria bloom or increase in number exponentially, they are considered that much more dangerous because of their ability to produce lethal toxins. This occurred in the southern IRL and the St. Lucie River last year when record freshwater discharges along with excess nutrients fueled the bright green bloom of an ordinarily freshwater cyanobacteria, Microcystis, creating a toxic stew and consequently a human and faunal health hazard.
We have our work cut out for us to restore our habitats and to change our environmental regulations to control nutrients in our priceless estuaries. These habitats are much too important to our health, our economy and our quality of life to let them slide down this slippery slope.