"Help! It's an HAB!"

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Harmful algal blooms (HABs) negatively impact organisms in a variety of ways that can range from cell and tissue damage to organism death. Although toxin production is one of the major mechanisms by which the blooms cause such severe damage (for more information, see "Tracing the Toxins"), there are several other consequences of HABs.

Gill irritation – Some HAB species, specifically spine-forming diatoms and mucus-producing algae, cause significant problems for fish and crustaceans. When large numbers of spiny phytoplankton or excess mucus gets caught in the animals' gills, the animals can experience respiratory failure.

Starvation – Many harmful algal species actually cause other organisms to starve to death. Some species interfere with the feeding mechanisms of zooplankton; others are unpalatable due to a mucus layer, size restrictions, or taste. And finally, some HAB species that are palatable to zooplankton have such poor nutritive value, the zooplankton actually starve even though they are physically eating.

Poor reproduction – Some plankton and filter feeders are capable of consuming HAB species, but exhibit decreased reproductive success as a result. For this reason, a consequence of many blooms has included a decrease in species abundance and diversity.

Predation – There is evidence that another capability of at least one harmful algal species is predation. After killing the fish or at least making it lethargic, Pfiesteria piscicida digests the fish tissue.

Anoxia and reduced water quality – High concentrations of decomposing and respiring cells can contribute to anoxic conditions and the formation of toxic sulfides in the water. The lack of oxygen, in addition to the production of sulfides, creates a deadly scenario for most marine life.

Reduced light penetration – Dense blooms of harmful algal species can significantly reduce the light penetration in the water column. This negatively impacts the survival of seagrasses that depend on the sunlight to provide their energy for photosynthesis.

So, what can we do about HABs? Scientists, governments, non-profit groups and industries are currently trying to decide how to answer that important question. Many suggestions have been proposed to mitigate the effects of HABs and to develop technologies to help detect and prevent blooms in the future. These suggestions range from developing monitoring programs that provide early detection of harmful algal blooms, to introducing a potential pathogen to kill the bloom. Many of the techniques have been tested and some of them have even been incorporated in certain regions of the world (technique list). The most challenging aspect of dealing with HABs is that any action taken to control the bloom can have enormous impact on the rest of the environment.

  • Understand the numerous impacts of harmful algal blooms.
  • Understand the advantages and disadvantages of the techniques being used and tested to detect and deal with harmful algal blooms
  • Recognize the consequences of various treatment techniques on the environment
  • Appreciate the complexity in choosing a appropriate detection or treatment technique in dealing with harmful algal blooms

The students should already be familiar with the integral role of algae in the food web and some of the implications of harmful algal blooms in the environment. This may have been accomplished by completing “Fitting Algae into the Food Web” and “Tracing the Toxins.” Other informative sources include Bigelow's "Toxic and Harmful Algal Blooms," and NOAA's State of the Coast Report on Harmful Algal Blooms.

Finding a "Cure?"

Note to teachers: Click here to see the printable version of this activity.

Preventing and eliminating harmful algal blooms are not easy tasks. There are numerous factors that influence the formation, distribution and duration of blooms. As you know, it’s difficult to control one factor in the environment, let alone all factors for all algae in all locations. In addition, any action taken to prevent or to remove a bloom has consequences for the other organisms in the environment.

Your class is going to evaluate the techniques that have been proposed, tested, and in some cases are being used to detect, prevent and control HABs and their effects.

As a class, compile a list of possible detection, prevention and control techniques that have been used or have been proposed for use in dealing with HABs. Some suggestions of some techniques that could be included in your list can be found here.

Divide the different techniques between lab groups. Each group is responsible for investigating their assigned techniques and presenting their findings to the rest of the class. Topics you want to make sure to include in your report are:

1) Description of the technique
2) Purpose of the technique (e.g. detection, prevention, remediation)
3) Current state of the research on this technique
4) Has this technique been used in real-world applications? When and where? With what results?

The results from your class research will be compiled in a summary table that can be created on the chalk/marker board or on poster board. After each group gives their presentation, your class will discuss the costs and benefits of the technique that was just presented. The results of the discussion will then be entered on the summary table to compare the advantages and disadvantages of each technique. A simple example table is shown below. Although only one advantage and one disadvantage is listed in the table below, you will most likely have more than one of each for every technique.

Mouse bioassay Detection works well for monitoring overall toxicity does not provide information on levels of individual toxins
Treating ballast water with algicide Prevention prevents transport of algae by ballast exchange effects of releasing algicide-treated ballast water into environment is unknown
Copper sulfate addition Remediation effective at killing algal cells costly procedure and results are short-lived

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This table summarizes the McREL science standards that are met through this lesson. To see a detailed list of standards that this lesson addresses, please click here.

Grade Level
Primary (K-2)
Elementary (3-5)  
Middle (6-8)  
High School (9-12)  

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