The Effects of Algae Blooms

Effects on Water

• When an algal bloom occurs, tiny, microscopic algae (also called phytoplankton) multiply rapidly because of the increased presence of phosphorous and nitrogen that the algae use in the process of photosynthesis and reproduction. The rapid reproduction and death of trillions of algae cells causes the water in which the algae live to become tinted green, yellow or red, depending on the type of algae in the water. The water also becomes very nitrogen-rich and oxygen-depleted because of the rapid growth and decay of the algae.

Effects on Aquatic Organisms

• Algae blooms often have a very negative effect on aquatic species. They can cause rapid and dramatic die-offs of many sea creatures, in some cases leading to the deaths of all other species in a confined, standing body of water. This occurs because oxygen in the water is consumed during the process of algae decay, leaving little to no oxygen for the other creatures to breathe. The other species suffocate under the layer of dead algae. Also, some algae contain toxins that are poisonous to other creatures.

Effects on Human Health

• Algal blooms also can have a negative effect on the health of humans. When humans consume seafood that has been infected by the toxins from an algal bloom, those toxins enter the body and cause them to become sick. For instance, a type of algae called Karenia brevis can bloom and produce large amounts of a toxin called brevitoxin. This toxin causes neurotoxic shellfish poisoning in humans; this toxin attacks the nervous system and can be fatal.

Effects on Commerce and Other Human Activities

• The fishing industry is often a victim of harmful algal bloom. When an algal bloom causes a rapid die-off of fish in a large body of water, fishermen either cannot fish or bring in a much smaller catch, which drastically lowers their revenues and, therefore, reduces their income. Beaches also may be forced to close when a red tide (an algal bloom in a coastal area) occurs, because of the danger of beachgoers becoming sick from contaminated water. Lastly, algal blooms can thwart the efforts of marine animal conservationists when species they are trying to protect are killed because of a harmful algal bloom.