By Regina Malczewski and Susan Hershberger
Algae can be beautifully bioluminescent in dark waters or show up in interesting colors near shore. But have you ever seen a “red tide”? Algae grow normally in the United States’ coastal waters … but when the growth gets out of control, it is called a harmful algal “bloom” (or HAB). This type of overgrowth releases excess chemicals into the water that can make fish, birds, and even humans sick.
How it starts
How blooms occur is not completely understood. Sometimes they happen naturally. But more intense and frequent blooms occur when there are too many nutrients in the water. Nutrient elements such as phosphorus and nitrogen can come from fertilizers used on farmlands that mix with water, especially after floods or hurricanes. These nutrients can become concentrated when water temperatures increase (which speeds up evaporation) or when there is a decrease in the flow of water over long periods.
What they look like
Blooms may look like foam, scum, mats, or paint floating on water. They may be red or brown in color, but can also appear blue, green, or no color at all. The pigments (in addition to chlorophyll) in each type of algae give the bloom a certain color.
What is bad about algal blooms?
Different types of microalgae grow in different areas and the negative impacts vary. Some algae are gooey and clog fish gills. Certain blooms color the water, stink, and even release harmful gases. There are others that kill coral reefs by producing toxins (chemicals that can be poisonous to other living beings). Though toxin-producing algae make up only about 1% of all blooms, they are dangerous to aquatic organisms, wildlife, and humans alike.
Yarr, matey — beware the “red tide”!
Karenia brevis is an algal species found in waters off Florida and Texas that can turn the water red, which is where “red tide” gets its name. Algae may float in the air above the water because of waves and disturbances in the water. When inhaled, they can result in major breathing problems. Other algal toxins can cause stomach pain, vomiting, diarrhea, headache, or skin irritation. More serious reactions include muscle weakness and dizziness, liver and kidney problems, and, in rare cases, even death. Animals often drink this contaminated water and die within hours.
Algal blooms are also bad for business because they look so unattractive. Dead aquatic animals often wash ashore and eating contaminated fish or crustaceans could be unsafe!
How can we stay safe?
These types of blooms can indicate changes in the environment that need our attention, such as climate change. However, there is no quick fix for HAB. The National Oceanographic and Atmospheric Administration (NOAA) looks for signs of blooms and collects data on water quality to try to predict where blooms are likely to occur. Blooms can also be seen from space, and satellite images help with predictions.
The next time you hear about a “red tide” or other types of HAB, think about what might be causing them. It is yet another reason to take better care of our environment!
Regina Malczewski is a retired biochemist who worked at the Dow Corning Corporation. Susan Hershberger is Director of the Center for Chemistry Education at Miami University in Oxford Ohio.