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Harmful Algal Blooms

How can we predict and reduce these ecologically and economically harmful events?

Every drop of water from a body of water is full of algae. Most of them are the beneficial. We need those algae because they are the base of the food web for all marine life. Unfortunately, a small fraction of that algal community can be harmful. The question that scientists who are studying the increasingly problematic topic of harmful algal blooms are asking now is: How and why can one species become dominant in that small drop of water?

Ecologist Pat Glibert has researched these diverse microorganisms at the University of Maryland Center for Environmental Science’s Horn Point Laboratory since 1986. Her work has taken her across the globe to study and aid in the prevention, management, and understanding of harmful algal blooms, a dangerous environmental phenomenon that is on the rise.

Phytoplankton, the subject of Glibert’s work, are microscopic algae that play a number of roles on Earth, from being the base of the food chain and producing oxygen to consuming carbon dioxide, but they have recently made headlines for causing harmful algal blooms, such as the red tide in Florida and the Gulf of Mexico.

There are hundreds of recorded instances of harmful algal blooms across the globe going back hundreds of years, but it was not until consistent tracking and investigation of these events that scientists linked many of these algal blooms to nutrient pollution from sources such as sewage treatment plants and runoff from agricultural lands.

Nutrient pollution causes an abundance of food for nutrient-loving algae, which allows them to grow uncontrollably and overwhelm ecosystems. The mass amounts of algae in turn affect the ecosystem by reducing the amount light photosynthetic organisms receive, and at times releasing toxins into the air and water. Their death can also create low-oxygen environments, called dead zones, which are also increasing common in estuaries such as Chesapeake Bay and many coastal areas.

Each harmful species carries its own potential negative impacts, from pure overabundance that blocks light and smothers other sea life, to producing toxins that cause fish kills and impacts human health. As is the case with poisonous plants on land, each harmful microscopic species can produce unique toxins.

Additionally, while we assume harmful algal blooms are caused by algae–which implies plant-like, or photosynthetic organisms–this is not always the case. Many of these small organisms can also eat other microorganisms and also carry out the process of photosynthesis. These organisms fall into a category called mixotrophs (they have mixed forms of nutrition) and are considered “the Venus fly traps of the microbial world,” complicating our understanding of these events.

When looking at harmful algal blooms, we are also working to understand what tributaries are contributing to pollution. If you stop something at the source, you have more containment of the event.

Pat Glibert


For a long time, it was thought that “dilution is the solution to pollution,” but nutrient loads may increase with runoff. The nutrients, such as phosphates and nitrates used as fertilizers on farms and lawns, can flow off the land into streams, rivers, and other bodies of water. This runoff can also be accelerated by heavy rains and large storms. These nutrients are not necessarily fully diluted when they reach tributaries throughout the watershed, instead putting these nutrients in waters where they can promote the growth of these microscopic algae.

Harmful algal blooms exist in different regions, consist of different species, and have differing health impacts, and scientists are using years of research to understand, track, and model these situations to prevent further environmental, economic, and human health impacts.

Glibert has worked with scientists and ecosystem managers worldwide to help reduce the spread of events when they occur and reduce the instances of harmful algal blooms. She is currently studying the devastating algal bloom that is ongoing in Florida, which has resulted in more than a thousand tons of dead fish and has contributed to considerable economic harm to the region.

More recently, Glibert has been working with Ming Li from UMCES’ Horn Point Laboratory developing mathematical models to track and predict harmful algal blooms. Li uses his expertise in modeling while Glibert contributes her years of experimental and physiological data on algal blooms.

Their most recent paper takes a look at how models can be used to understand how the frequency of blooms may change in a changing climate. Changes in climate include not only increasing temperatures, but also changes to precipitation and storm frequency. They are using models to ask the question “What will blooms look like in the year 2050?”

Climate models show that while Maryland summers are projected to be hotter and drier, springs are getting hotter, wetter, and stormier, which can in turn exaggerate harmful algal blooms. Using this collection of models and understanding of when blooms occur, under which conditions, and what temperature, nutrient, and salinity conditions, we can better deal with the negative effects from the blooms.

“We may see the earlier onset of blooms, we may see longer blooms, but the summer may show a bit of a decline because waters get too warm for some of the species we are concerned about,” said Glibert.  

Coming up with solutions that can be fully implemented to avoid and get rid of these blooms is still far off, but by working to project when and where they occur scientists can help inform ecosystem managers and aid in their preparation for these events.

In addition to helping develop models and aiding in bloom management, Glibert is writing a book on phytoplankton, targeted towards beginning graduate students. It will cover how algae function, who are they, what are the factors driving their growth, and what are the major trends we are seeing. While harmful algae are considered in the book, the aim of the book is more comprehensive, covering the biology of the favorable–as well as the unfavorable–algae.

“There is a lot of work yet to be done. The easiest solution is to keep these events from occurring in the first place,” said Glibert.