An algae problem

Southwest Florida, no doubt, has an algae problem. Actually it has more than one algae problem. The major culprits at the moment are Karenia brevis (the Florida red tide) along our coast and a couple species of Microcystis in the Caloosahatchee River.

Karenia brevis, is a dinoflagellate that is found almost exclusively in the Gulf of Mexico. Dinoflagellates are microscopic algae comprised of approximately 2,000 species worldwide. Most are harmless, but some, such as our Florida red tide, are toxic. Scientists know that K. brevis blooms originate 10-40 miles offshore and winds and currents bring them inshore, usually in bottom waters. K. brevis can use many different forms of nitrogen and phosphorus and the sources of these nutrients may differ between the offshore, nearshore, and estuarine environment.

There is no direct link between human derived nutrients (fertilizers, sewage, etc.) and the initiation of blooms, however, once blooms are transported inshore, these nutrient sources can fuel or sustain them. The current bloom we’re experiencing, started last November. Blooms lasting this long are not unheard of. In 2005, a massive red tide, spanning more than 500 square miles, lasted seventeen months. Like all blooms, the 2005 one moved around, and ebbed and waned in size and intensity. And, like this one, it resulted in the wide spread death of marine life. Although we were impacted by the 2005 bloom, the Tampa Bay region and areas north experienced the brunt of that bloom.

Moving to the Caloosahatchee River, two species of Microcystis comprise the majority of this bloom. Microcystis is a cyanobacteria, also referred to as blue-green algae. Although we refer to it as an algae, cyanobacteria are actually far more primitive than true algae, having appeared 3.5 billion years ago. In fact, they were the first organisms to photosynthesize and produced the oxygen in our atmosphere. There are 2,698 described cyanobacteria species. Microcystis is the most common bloom-forming genus, and is almost always toxic. Although blooms of Microcystis and other cyanobacteria species are often lumped in with other harmful algae blooms (HABs), they are more accurately known as cyanobacterial HABs, or cyanoHABs.

In ponds, lakes and rivers, HABs are most frequently caused by cyanobacteria; however, in estuarine and marine waters, dinoflagellates cause the majority of HABs. One thing all HABs have in common is their dependence on nutrients for initiation and maintenance. Until recently, scientists focused on nitrogen in our estuaries and phosphorus in freshwater systems. That is because most of our estuaries are nitrogen limited whereas most freshwater systems are phosphorus limited. Today we know that we have to be concerned with both nitrogen and phosphorus in all of our waterbodies.

When our lakes, rivers, estuaries and oceans are healthy, naturally occurring microscopic algae, also called phytoplankton, are limited by the availability of nutrients and phytoplankton feeding organisms. When land based activities deliver nutrients to the water in excess, it can lead to a process called eutrophication. Consequences of eutrophication include algal blooms, fish kills, dead zones and loss of bottom habitats.

Aside from the big fixes to clean up and restore water flow to the Everglades, there are a number of other land use practices that can help to reduce the amount of nutrients entering our waterbodies including: converting conventional septic systems to centralized sewer or advanced treatment systems, reducing agricultural and urban fertilizer use to recommended levels, and controlling runoff from fertilizers and animal waste – agricultural and domestic, and smart development solutions that better integrate stormwater management options.

Although most management activities to date have attempted to reduce nutrient loading from the watershed (land area draining to a surface water), it is also important to consider the cycling and removal of nutrients from within the receiving waterbodies by sediments; plants such as mangroves, saltmarsh and seagrass; and animals such as bacteria, oysters and clams. For instance, suspension feeding organisms, which include filter feeders – such as clams, oysters, tunicates, and some fish like the Atlantic thread herring (greenie) and Gulf menhaden, potentially influence nutrient cycling, water clarity, phytoplankton abundance, and other ecosystem processes.

Interestingly, Mote Marine Laboratory is currently doing a study to evaluate whether filter feeding animals and seaweeds can help mitigate the effects of K. brevis. A number of other projects are also being planned or are underway to evaluate and/or restore vital habitat and organisms in our waters to mitigate nutrient inputs.

In order to restore water quality and reduce the frequency and impact of harmful algal blooms in Florida, we have to focus on both the land and the water. Everyone has a role in affectively controlling the nutrients that threaten our coastal environments and the economies that depend on them.


Feature image of the Caloosahatchee River courtesy of USGS

O’Neil, Judisth M. and Cynthia A. Heil (Ed). 2014. Nutrient dynamics of Karenia brevis red tide blooms in the eastern Gulf of Mexico, Harmful Algae, 38:1-140.

Kellogg, M. Lisa, Ashley R. Smyth, Mark W. Luckenbach, Ruth H. Carmichael, Bonnie L. Brown, Jeffrey C. Cornwell, Michael F. Piehler, Michael S. Owens, D. Joseph Dalrymple, Colleen B. Higgins. 2014. Use of oysters to mitigate eutrophication in coastal waters, Estuarine, Coastal and Shelf Science, 151:156-168.

Smyth, Ashley R., Anna E. Murphy, Iris C. Anderson, Bongkeun Song. 2017. Differential Effects of Bivalves on Sediment Nitrogen Cycling in a Shallow Coastal Bay, Estuaries and Coasts, 41:1147–1163.

Myszewski, Margaret A. and Merryl Alber, 2016. Living Shorelines in the Southeast: Research and data gaps. Report prepared for the Governor’s South Atlantic Alliance by the Georgia Coastal Research Council, University of Georgia, Athens, GA, 35 pp.


Posted: August 2, 2018

Category: Coasts & Marine, Conservation, Natural Resources, Water
Tags: Algae, K. Brevis, Microcystis, Red Tide, Water Quality

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