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Warm Temperatures Bring Cyanobacteria Blooms to Sarasota Bay

It’s hard not to notice some strange stuff surfacing in many areas around our bays this summer. The Florida Department of Environmental Protection’s Algae Bloom Monitoring and Response team identified Lyngbya majuscula, a type of cyanobacterium, in many bays between Anna Maria Island and Venice in May and June. Many of those blooms are still visible as they decompose. Another species of cyanobacteria, Aphanizomenon flos-aquae, was detected in the freshwater reaches of the Manatee River in early July. FDEP is working to identify other samples taken around the region. (Click here to see sampling locations and results in an interactive map.)

What is Lyngbya majuscula?

Lyngbya majuscula is a type of cyanobacterium, meaning that it is part of a group of bacteria that obtain energy through photosynthesis. Cyanobacteria are commonly known as “blue-green algae.” While some cyanobacteria cause harmful algae blooms (HABs), most are beneficial. Their ranks include Prochlorococcus, a genus of tiny marine cyanobacteria that are some of the most important oxygen-producers on Earth.

Lyngbya species are found in coastal tropical and subtropical waters worldwide. L. majuscula is only one of several species of Lyngbya found in central and southern Florida waters.

Lyngbya cyanobacteria in water

Lyngbya majuscula at Blackburn Point Park in May 2019. Photo courtesy Florida Department of Environmental Protection.

How do Lyngbya mats form?

Lyngbya blooms have been tied to water temperature increases and to pulses of nutrient sources including nitrogen, iron, and phosphorus. Lyngbya majuscula blooms form in sediments, eventually covering bay bottom habitats such as oyster reefs and seagrasses. However, blooms can sometimes photosynthesize so rapidly – and produce so much oxygen in the process – that oxygen is trapped in the filaments of the mats, causing the mats to dislodge from the bottom and float to the surface of the water. When this floating Lyngbya accumulates and begins to decompose, the odor can be quite bad.

How do Lyngbya blooms impact Sarasota Bay?

Lyngbya is a natural component of the Sarasota Bay ecosystem and some amount of bloom activity happens every year. However, especially large blooms can smother bay bottom habitats, including seagrasses. If the bloom large enough and lasts for an extended period, it can cause seagrass die-offs by restricting light availability. When the bloom dies and begins decomposing, it can cause decreases in dissolved oxygen, which may lead to fish kills.

Research has indicated that Lyngbya species produce “secondary metabolites,” compounds that deter grazers such as fish and crabs from feeding on them.

Some Lyngbya blooms can impede boat navigation, but this is usually only a problem in freshwater systems.

How can we manage Lyngbya blooms?

Both climate change and increases in nutrient inputs to coastal waters could increase the frequency and severity of Lyngbya blooms. We can manage Lyngbya blooms by reducing inputs of nitrogen, phosphorus, and iron to inland and coastal waters. Click here to learn how you can reduce your own nutrient footprint.

Citizens can report algae blooms to the Florida Department of Environmental Protection using this form or by calling 855-305-3903.

Where can I learn more about Lyngbya and other kinds of cyanobacteria?

Florida Sea Grant: Resources for understanding blue-green algae (cyanobacteria) blooms

Florida Sea Grant: Harmful Algae Blooms Affecting Florida’s Coast

NOAA ECOHAB project fact sheet

NOAA ECOHAB project newsletter

FWC – Cyanobacteria

FDEP – Algal Bloom Monitoring and Response