Harmful algal bloom

A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that can harm other living things. HABs can hurt animals, the environment and local economies. They are happening more often around the world, and many experts think this is linked to global climate change.

HABs happen because of eutrophication, which means there is too much food for the algae in the water. The most common foods are fixed nitrogen (nitrates, ammonia, and urea) and phosphate. These extra nutrients come from places like agriculture, factories, too much fertilizer use in cities and towns, and urban runoff. Warm water and when the water does not move much can also help HABs grow.

When these blooms die, tiny living things called microbes break them down and use up oxygen. This can create a "dead zone" where there is not enough oxygen for fish to live, leading to fish die-offs. These events can happen without people, but things people do, like using fertilizer and pollution, often make them worse. The U.S. National Oceanic and Atmospheric Administration (NOAA) expects to see more harmful blooms in the Pacific Ocean.

Description and identification

Harmful algal blooms (HABs) from cyanobacteria, also called blue-green algae, can look like foam, scum, or a mat on the water's surface. They may be bright green or other colors, depending on their pigments. These blooms are a problem all over the world, especially in warm waters that have too many nutrients.

These blooms can be harmful because they make toxins or use up oxygen in the water. This can hurt fish and other animals. Not all algal blooms are harmful — some only change the color or smell of the water. To know if a bloom is harmful, scientists take samples and study them under a microscope or use special tools to detect toxins.

Terminology

Harmful algal blooms, sometimes called "red tides," are large groups of algae that can harm other living things. These blooms can be harmful because they release toxins that affect other species. They can also create "dead zones" where there is too little oxygen for sea creatures to survive.

The name "red tide" comes from blooms of certain tiny organisms, like Karenia brevis, but this name can be confusing. Algal blooms can be many colors, and their growth is not related to the tides. Not all red tides are caused by these organisms; some are created by other tiny plants. Scientists now use more precise names like "harmful algal bloom" for harmful species and "algal bloom" for those that are not harmful.

Main article: Red tide
Main articles: Algal bloom, Algal bloom#Harmful_algal_bloom

Types

There are three main types of tiny floating organisms that can form harmful algal blooms: cyanobacteria, dinoflagellates, and diatoms. These organisms can make their own food from sunlight through photosynthesis, which helps small fish and other sea creatures.

Cyanobacteria, often called blue-green algae, can produce toxins that may harm animals and people. Diatoms and dinoflagellates are mainly found in ocean areas and can also form harmful blooms, sometimes helped by human activities. Some of these algae produce toxins that can hurt animals and people if they eat affected seafood.

Causes

Sometimes it is hard to know what causes harmful algal blooms (HABs). In some places, HABs seem to happen naturally. In other places, human activities make them happen more often. Many different algae can form HABs, and each needs different conditions to grow.

The growth of algae is usually limited by the amount of nitrates and phosphates available. These nutrients can be plentiful in coastal areas and from agricultural runoff. Other factors like iron, silica, and carbon can also affect algal blooms. Human-caused factors such as water pollution and rising sea water temperature may also contribute to HABs.

Nutrients

Further information: Eutrophication

Nutrients get into water from agricultural pollution, urban runoff, and sewage treatment plants that lack proper nutrient control. Coastal areas, especially places like the Mediterranean Sea, often receive untreated sewage. This adds more nutrients to the water. These extra nutrients can lead to more frequent and severe HABs.

Iron fertilization

Main article: Iron fertilization

Adding iron to ocean areas that lack it can encourage the growth of phytoplankton. This is done to help remove carbon dioxide (CO₂) from the air. Iron is important for plants to make food through photosynthesis.

Climate change

Further information: Effects of climate change on oceans

Climate change leads to warmer waters. This creates better conditions for algae to grow in more places, including areas farther north. Warmer water and high-nutrient conditions in lakes and rivers increase the chance of HABs.

Causes or contributing factors of coastal HABs

HABs often appear as discolored water, sometimes reddish-brown. While they are a natural event, the exact reasons they happen are not always known. Natural factors like salt levels, temperature, and wind can play a role. Human activities, such as water pollution from sewage and agricultural runoff, can also contribute. In some places, HABs occur naturally due to ocean currents, while in others, they result from extra nutrients caused by humans. Factors like dust from deserts and climate patterns such as El Niño can also influence HABs.

Number and sizes

The number of harmful algal blooms has been going up around the world. Scientists are not sure if there are more blooms or if we are just getting better at finding them.

These blooms have been seen in many places, including Europe, Africa, Australia, and India. They have even appeared in surprising spots like the Arctic, Antarctica, and mountain ranges such as the Himalayan Mountains, the Rocky Mountains, and the Sierra Nevada Mountains. In the United States, every coastal state has dealt with harmful algal blooms in recent years. Major rivers, like the Ohio River, have also had big blooms that can stretch for hundreds of miles. Climate change may make these blooms happen more often in the future. Off the coast of South Africa, certain blooms happen every spring and can make shellfish unsafe to eat.

Harmful effects

Further information: Eutrophication § Effects

As algal blooms grow, they use up oxygen in the water and block sunlight from reaching fish and plants. These blooms can last for days or months. Without enough light, plants under the bloom may die, and fish may starve. At night, the dense algae use oxygen, lowering its levels. When the algae die, tiny organisms that break down the dead algae also use more oxygen, which can cause more fish to die or leave the area.

If oxygen levels keep dropping, it can create areas called dead zones where fish and plants cannot survive. These dead zones can also release methane, a gas that traps heat in the atmosphere. Scientists think that harmful algal blooms played a role in some of Earth’s biggest events where many plants and animals died long ago.

Human health

Some toxins from algal blooms can be breathed in from the air near affected waters, which may affect health. Not all blooms release harmful toxins into the air; it depends on the type of algae and the conditions. Toxins can be carried far by the wind.

Eating fish or shellfish from areas near blooms is not advised because these animals can collect toxins. This can lead to several types of poisoning in humans. In 1987, a new kind of poisoning was found after people ate mussels from Prince Edward Island. The toxin came from a type of algae in the water where the mussels grew. Other types of poisoning have also caused problems in places like the Philippines.

After a bloom in Monterey Bay, California, health officials warned people not to eat certain fish like anchovies, sardines, or crab caught there. In 2015, many shellfish fisheries in Washington, Oregon, and California closed because of high levels of toxins in shellfish. Breathing in vapors from waves during a bloom can sometimes cause breathing problems.

In 2018, officials in Utah worried that crops might get contaminated if watered with toxic water, though they said it was hard to measure.

People are usually warned not to drink or even touch water from algal blooms, and pets should stay away too. In 2014, Toledo, Ohio, told its residents not to drink tap water because a bloom in Lake Erie made the water unsafe. Similar issues happened in Kenya, China, and Australia.

Symptoms from drinking toxic water can include feeling sick, throwing up, or having trouble with digestion. In rare cases, it can be very serious. Touching the water might cause skin rashes or eye irritation.

Economic impact

Algal blooms can harm tourism and recreation. In places like Florida, California, and Utah, people have avoided beaches and lakes because of the risks. This hurts local businesses. Similar issues have happened in Europe, including France.

The fishing industry also suffers. In 1976, a bloom near New York and New Jersey cost fisheries a lot of money. In 2009, a bloom in Hong Kong killed valuable fish. The U.S. seafood industry worries about losing money each year. In 2015, a huge bloom shut down shellfish fishing on the West Coast for the first time ever.

Environmental impact

Algal blooms can create dead zones where there isn’t enough oxygen for fish and other animals to survive. These dead zones can grow and rarely go away. One dead zone in the Black Sea got better after changes in farming practices.

Blooms can also kill fish directly. In 2016, a bloom in Chile killed many salmon being farmed. Fish die-offs have happened in many places, including Rio de Janeiro, Brazil, and Monterey Bay in the U.S.

Land animals like pets and livestock can also get sick or die from toxins in the water. Marine animals like dolphins, whales, and sea turtles have been harmed or killed by these toxins. Birds that eat contaminated fish have also died.

Harmful algal blooms can hurt many sea animals, including dolphins, sea turtles, seabirds, and fish. The toxins can affect their health in many ways. Some animals can even die from eating contaminated fish or shellfish.

Potential remedies

Further information: eutrophication § Reversal and remediation

Algal blooms can happen when too many nutrients, like nitrates and phosphorus from fertilizers, get into lakes and rivers, especially after heavy rains. Scientists suggest better farming methods to help stop this. For example, using drip irrigation gives water and fertilizer straight to plant roots. This means less fertilizer runs off into the water. Planting buffer zones with plants and wetlands can also trap nutrients before they reach the water.

Some chemicals can kill algae, but they might also harm fish and other wildlife. In certain places, new chemicals have been tested and worked well. For instance, Chippewa Lake in Ohio cleared its toxic algae quickly using a special treatment. Scientists are also looking at natural ways to control harmful algae. They are studying things like compounds from seaweeds and special clays that trap algae in the sediment, which can help reduce blooms.

Notable occurrences

Harmful algal blooms, also known as red tides, happen when algae grow too much and can harm fish, plants, and sometimes people. These blooms can happen in many places around the world.

Some important times when harmful algal blooms happened include:

• In 1793, a bloom was first recorded in British Columbia, Canada.
• In 1844, a possible bloom was seen off the Florida Gulf Coast.
• In 1901, bright glowing waters were seen in Southern California because of algae called Lingulodinium polyedrum.
• In 1972, a bloom in New England made shellfish dangerous to eat.
• In 1991, a huge bloom happened in the Darling River in Australia.
• In 2005, a bloom was found further south than usual along the U.S. East Coast.
• In 2008, big algae blooms caused damage in the Chesapeake Bay.
• In 2013, a bloom happened in China near Qingdao.
• In 2014, a bloom in Lake Erie made the water in Toledo, Ohio, unsafe to drink.
• In 2017 and 2018, a serious bloom in Southwest Florida hurt fish, dolphins, and manatees.

Blooms keep happening in many places, like off the coast of Florida, in the Gulf of Mexico, and in lakes such as Lake Erie. These blooms can close beaches, hurt fishing, and sometimes make the water unsafe.