Algal Blooms

What Are Algal Blooms?

Algae are plantlike organisms that form the base of the food web in marine and freshwater systems. They’re always present at low levels. We usually divide algae into two groups:

• Microalgae are microscopic, single-celled organisms.
• Macroalgae, which many people refer to as seaweed, are multicellular and can grow as large or larger than other aquatic plants.

Algae feed on the nutrients (nitrogen and phosphorus) in the water column, similarly to how landscape plants take up fertilizers. In natural systems, either nitrogen or phosphorus eventually depletes from the water, helping limit algal growth.

Learn more about the plants and animals that live in the Indian River Lagoon (IRL).

What Causes Algal Blooms in the IRL?

Periods of warm water and the presence of excessive nutrients can cause algae to rapidly grow out of control, or “bloom.” When this happens, foams, patches or streaks form on top of the water that wind and waves can push to shore.

The color of algal blooms is related to which species is blooming. While algal blooms can be a nuisance, not all blooms are harmful. Those that are harmful are called harmful algal blooms (HABs).

How Harmful Algal Blooms Affect the Lagoon

One type of HAB can release toxins, which are chemicals that can cause acute illness or even death in animals and people. In Florida, these HABs occur in all types of water bodies, and they affect nearly every coastal community from time to time.

HABs can also be nontoxic. This type of HAB damages other organisms simply due to the massive number of cells produced during a bloom, when cells can number in the millions per liter.

At such concentrations, blooms can block sunlight to the point where seagrasses and other marine plants die. Some species also produce mucus or spines that clog the gills of fishes and invertebrates, causing suffocation.

Environmental effects from HABs include direct impacts such as seagrass loss, low oxygen in water bodies and mortalities in fish and wildlife. Indirect impacts include economic effects from lost tourism revenue, public health concerns and consumer avoidance of goods perceived as tainted by toxins.

How You Can Help Prevent Algal Blooms in the IRL

In the IRL, algal blooms are part of a bigger story of excess nutrients, slow flushing and stressed habitats. Cutting nutrient pollution on land helps limit blooms in the water and supports the lagoon’s long-term recovery.

To help prevent algal blooms, learn how to live lagoon-friendly and reduce nutrient pollution.