Algal bloom - WikiHQ

thumb|300px|A very large algae bloom in [[Lake Erie, North America, which can be seen from space]]

An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in fresh water or marine water systems. It may be a benign or harmful algal bloom.

Algal bloom is often recognized by the discoloration in the water from the algae's pigments. The term algae encompasses many types of aquatic photosynthetic organisms, both macroscopic multicellular organisms like seaweed and microscopic unicellular organisms like cyanobacteria. Algal bloom commonly refers to the rapid growth of microscopic unicellular algae, not macroscopic algae. An example of a macroscopic algal bloom is a kelp forest.

Description

The term algal bloom is defined inconsistently depending on the scientific field, and can range from a "minibloom" of harmless algae to a large, harmful bloom event. Since algae is a broad term including organisms of widely varying sizes, growth rates, and nutrient requirements, there is no officially recognized threshold level as to what is defined as a bloom. Because there is no scientific consensus, blooms can be described and quantified in several ways: measurements of new algal biomass, the concentration of photosynthetic pigment, quantification of the bloom's negative effect, or relative concentration of the algae compared to the rest of the microbial community.

concentration of chlorophyll exceeding 5 μg/L,
concentration of the species considered to be blooming in excess of 1000 cells/mL, and
algae species concentration simply deviating from its normal growth.

Blooms are the result of a nutrient needed by the particular algae being introduced to the local aquatic system. This growth-limiting nutrient is typically nitrogen or phosphorus, but can also be iron, vitamins, or amino acids. Along coastal regions and in freshwater systems, agricultural, city, and sewage runoff can cause algal blooms.

Algal blooms, especially large algal bloom events, can reduce the transparency of the water and can discolor it. Blooms may also consist of macroalgal (non-phytoplanktonic) species. These blooms are recognizable by large blades of algae that may wash up onto the shoreline.

Once the nutrient is present in the water, the algae begin to grow at a much faster rate than usual. In a mini bloom, this fast growth benefits the whole ecosystem by providing food and nutrients for other organisms.

File:Ocean phytoplankton bloom feed by the Amazon River.jpg|alt=Rivers, such as the Amazon, deposit nutrients from land into South America's tropical ocean waters, leading to thick blooms along the coastline |Rivers, such as the Amazon, deposit nutrients from land into South America's tropical ocean waters, leading to thick blooms along the coastline.

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Freshwater algal blooms

thumb|Cyanobacteria activity turns [[Coatepeque Caldera lake into a turquoise color.]]

Freshwater algal blooms are the result of an excess of nutrients, particularly some phosphates. Excess nutrients may originate from fertilizers that are applied to land for agricultural or recreational purposes and may also originate from household cleaning products containing phosphorus.

The reduction of phosphorus inputs is required to mitigate blooms that contain cyanobacteria. In lakes that are stratified in the summer, autumn turnover can release substantial quantities of bio-available phosphorus potentially triggering algal blooms as soon as sufficient photosynthetic light is available. Excess nutrients can enter watersheds through water runoff. Excess carbon and nitrogen have also been suspected as causes. Presence of residual sodium carbonate acts as catalyst for the algae to bloom by providing dissolved carbon dioxide for enhanced photosynthesis in the presence of nutrients.

When phosphates are introduced into water systems, higher concentrations can cause increased growth of algae and plants. Algae tend to grow very quickly under high nutrient availability, but each alga is short-lived, and the result is a high concentration of dead organic matter which starts to decompose. Natural decomposers present in the water begin decomposing the dead algae, consuming dissolved oxygen present in the water during the process. This can result in a sharp decrease in available dissolved oxygen for other aquatic life. Without sufficient dissolved oxygen in the water, animals and plants may die off in large numbers. This may also be known as a dead zone.

Blooms may be observed in freshwater aquariums when fish are overfed and excess nutrients are not absorbed by plants. These are generally harmful for fish, and the situation can be corrected by changing the water in the tank and then reducing the amount of food given.

Natural causes of algal blooms

Algal blooms in freshwater systems are not always caused by human contamination and have been observed to occur naturally in both eutrophic and oligotrophic lakes. Eutrophic lakes contain an abundance of nutrients such as nitrogen and phosphates which increase the likelihood for blooms. Oligotrophic lakes don't contain much of these nutrients. Oligotrophic lakes are defined by various degrees of scarcity. The trophic state index (TSI) measures nutrients in freshwater systems and a TSI under 30 defines oligotrophic waters. Algal blooms in oligotrophic bodies of water have also been observed. This is a result of cyanobacteria which cause blooms in eutrophic lakes and oligotrophic lakes despite the latter containing a lack of natural and man-made nutrients.

Nutrient uptake and cyanobacteria

A cause for algal blooms in nutrient-lacking environments come in the form of nutrient uptake. Cyanobacteria have evolved to have better nutrient uptake in oligotrophic waters. Cyanobacteria utilize nitrogen and phosphates in their biological processes. Because of this, cyanobacteria are known to be important in the nitrogen and phosphate fixing cycle in oligotrophic waters.

Cyanobacteria are able to retain high phosphorus uptake in the absence of nutrients which help their success in oligotrophic environments. Cyanobacteria species such as D. lemmermannii are able to move between the hypolimnion which is rich in nutrients such as phosphates and the nutrient-poor metalimnion which lacks phosphates. This overabundance in nutrients leads to blooms.|350x350px]]

Turbulent storms churn the ocean in summer, adding nutrients to sunlit waters near the surface. This sparks a feeding frenzy each spring that gives rise to massive blooms of phytoplankton. Tiny molecules found inside these microscopic plants harvest vital energy from sunlight through photosynthesis. The natural pigments, called chlorophyll, allow phytoplankton to thrive in Earth's oceans and enable scientists to monitor blooms from space.

The NAAMES study conducted between 2015 and 2019 investigated aspects of phytoplankton dynamics in ocean ecosystems, and how such dynamics influence atmospheric aerosols, clouds, and climate.

In France, citizens are requested to report coloured waters through the project PHENOMER. This helps to understand the occurrence of marine blooms.

Wildfires can cause phytoplankton blooms via oceanic deposition of wildfire aerosols.

Harmful algal blooms

thumb|A satellite image of [[phytoplankton swirling around the Swedish island of Gotland in the Baltic Sea, 2005]]

A harmful algal bloom (HAB) is an algal bloom that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. The diversity of these HABs make them even harder to manage, and present many issues, especially to threatened coastal areas. HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisonings. Due to their negative economic and health impacts, HABs are often carefully monitored.

HAB has been proved to be harmful to humans. Humans may be exposed to toxic algae by direct consuming seafood containing toxins, swimming or other activities in water, and breathing tiny droplets in the air that contain toxins. Because human exposure can take place by consuming seafood products that contain the toxins expelled by HAB algae, food-borne diseases are present and can affect the nervous, digestive, respiratory, hepatic, dermatological, and cardiac systems in the body.

Beach users have often experienced upper respiratory diseases, eye and nose irritation, fever, and have often needed medical care in order to be treated. Ciguatera fish poisoning (CFP) is very common from the exposure of algal blooms. Water-borne diseases are also present as our drinking waters can be contaminated by cyanotoxins.

If the HAB event results in a high enough concentration of algae the water may become discoloured or murky, varying in colour from purple to almost pink, normally being red or green. Not all algal blooms are dense enough to cause water discolouration.

Bioluminescence

Dinoflagellates are microbial eukaryotes that link bioluminesce and toxin production in algal blooms. They use a luciferin-luciferase reaction to create a blue light emission glow. There are seventeen major types of dinoflagellate toxins, in which the strains, Saxitoxin and Yessotoxin, are both bioluminescent and toxic. These two strains are found to have similar niches in coastal areas. A surplus of Dinoflagellates in the night time creates a blue-green glow, however, in the day, it presents as a red brown color which names algal blooms, Red Tides. Dinoflagellates have been reported to be the cause of seafood poisoning from the neurotoxins.

Monitoring and forecasting

Historically, forecasting algal blooms relied heavily on physical water sampling and hydrodynamic modeling. While accurate, these methods can be resource-intensive and struggle to rapidly process highly complex, changing environmental variables. Consequently, modern forecasting increasingly integrates remote sensing with machine learning to complement traditional physical models.

Open-science initiatives have helped accelerate these algorithmic approaches. For example, during the 2019 NASA International Space Apps Challenge, a student team demonstrated how convolutional neural networks could analyze satellite data to predict cyanobacteria concentrations up to a month in advance. In formal scientific literature, recent frameworks employ self-supervised deep learning to fuse multi-sensor and hyperspectral satellite datasets. These models help generate early warning systems for coastal communities and water treatment facilities.

Despite these advancements, satellite-based forecasting faces inherent limitations. Algorithmic accuracy depends heavily on accounting for highly localized factors, such as regional eutrophication or sudden water temperature shifts. Furthermore, optical satellite measurements are frequently obstructed by cloud cover, requiring predictive models to rely on data interpolation to bridge missing gaps.

Management

There are three major categories for management of algal blooms consisting of mitigation, prevention, and control.

Within mitigation, routine monitoring programs are implemented for toxins in shellfish for early warnings and an overall surveillance of the area to monitor and quantify harmful algal blooms. The HAB levels of the shellfish will be determined and can manage restrictions to keep contaminated shellfish off the food market. Moving fish pens away from algal blooms is also another form of mitigation.

Within prevention, we can reduce surface runoff carrying excess nutrients by increasing the amount of permeable surfaces and vegetation. Permeable surfaces help absorb the runoff before it can make its way into the waterway. We can put into place permeable streets and parking lots which help allow for the pollution from vehicles and other runoff nutrients to be soaked up and/or slowed. HABs can lead to anaerobic (lack of oxygen) environments which can kill any organisms living within the water, fish poisoning, respiratory problems and illness among beach goers.

HABs have a large effect on the Great Lakes St. Lawrence River Basin. Invasive zebra and quagga mussels are positively correlated with their impact on the environment. These mussels increase the cycling of phosphorus which therefore increases harmful algae blooms in areas they are present. Harmful algae blooms continue to infect water supplies at the Binational Great Lakes Basin and due to the world's recovery from the COVID-19 pandemic, solving the issue has become a low priority. This economical problem has become part of politics in the United States, whereas in allied countries such as Canada there is low concern.

The impact of harmful algae blooms on the environment have a substantial effect on marine life. For example, in August 2024 the growth of the toxic algae, Pseudo-nitzschia, along California coasts were making sea lions sick and aggressive to beach goers. Scientists claim this is a seasonal occurrence. The growth of Pseudo-nitzschia leads to the production of a dominic acid which accumulates in fishes such as sardines, anchovies, and squids. This directly affects the food web and the primary food source of sea lions. Once the toxins are transferred via consumption, they can cause seizures, brain damage, and death to the animal. During this surge, people reported bites and unpredictable, aggressive behavior from the infected sea lions. In this sickened state, the sea lions are scared and act out of fear in order to protect themselves. Pregnant sea lions are most vulnerable to toxic algae poisoning and are more likely to die from the effects. This is primarily due to the heating of oceans and other bodies of water, which stimulates algae growth However, climate change can also result in a decrease in algae blooms, due to intense rainfall that can flush the blooms out of bodies of water.

Human interference

Alongside climate change, the increase in algae blooms can be attributed to human practices. In agriculture, the use of fertilizers can provide the necessary nutrients for algae growth, and enter the water cycle from surface runoff.