What is that green stuff floating on the water? – all about Azolla AKA Mosquito Fern
What is that green stuff floating on the water? – all about Azolla AKA Mosquito Fern
During warmer days in CA, you might notice a green colored (or reddish in full sun) carpet covering the surface of some ponds, lakes, & slow-moving waterways…
What is that green stuff ?
One likely candidate is a floating plant called Azolla filiculoides (or Azolla for short) often called Pacific Mosquito Fern. The common name comes from the belief that it is able to blanket water surfaces so thickly that it can prevent mosquitos from laying eggs & stop them from reproducing. This is likely false, although it is possible that large amounts may deter the survival of some of the larvae.
Azolla isn’t the only small floating plant you might see within the green floating carpet. Duckweed (Lemna sp.) is another common occupant of these spaces. At a distance the mat of green formed by these two plants might appear similar. However, if you look closely, you can see the differences between the two (see images). Azolla is actually a type of aquatic fern & does not belong to the duckweed family.
COMMON NAMES FOR AZOLLA
Azolla
Duckweed
(Note Azolla in upper right.)
During warmer days in CA, you might notice a green colored (or reddish in full sun) carpet covering the surface of some ponds, lakes, & slow-moving waterways…
What is that green stuff ?
One likely candidate is a floating plant called Azolla filiculoides (or Azolla for short) often called Pacific Mosquito Fern. The common name comes from the belief that it is able to blanket water surfaces so thickly that it can prevent mosquitos from laying eggs & stop them from reproducing. This is likely false, although it is possible that large amounts may deter the survival of some of the larvae.
Azolla isn’t the only small floating plant you might see within the green floating carpet. Duckweed (Lemna sp.) is another common occupant of these spaces. At a distance the mat of green formed by these two plants might appear similar. However, if you look closely, you can see the differences between the two (see images). Azolla is actually a type of aquatic fern & does not belong to the duckweed family.
COMMON NAMES FOR AZOLLA
Azolla
Duckweed
(Note Azolla in upper right.)
One of the things that sets Azolla apart from other plants is the symbiotic relationship it has with a cyanobacteria, Anabeana azollae, that lives within its cells. This cyanobacterium has the ability to fix nitrogen from the air & share this nutrient with the Azolla in which it lives. The relationship helps Azolla to fulfill its nitrogen requirements more easily thus allowing it to thrive in nitrogen-deficient waters.
One of the things that sets Azolla apart from other plants is the symbiotic relationship it has with a cyanobacteria, Anabeana azollae, that lives within its cells. This cyanobacterium has the ability to fix nitrogen from the air & share this nutrient with the Azolla in which it lives. The relationship helps Azolla to fulfill its nitrogen requirements more easily thus allowing it to thrive in nitrogen-deficient waters.
Note in the image above – Where the Azolla is shaded at the base of the reeds it is green in color & where it is further away & exposed to more sunlight it has turned reddish.
The color of Azolla can change in different conditions. Azolla often turns reddish or brown in color when growing under intense sunlight or when the plant is stressed. The red tinge is due to the production of anthocyanins within the leaflets of the fern. Research has shown that anthocyanins may play a protective role in helping plants survive extreme temperatures & herbivory.
Note in the image above – Where the Azolla is shaded at the base of the reeds it is green in color & where it is further away & exposed to more sunlight it has turned reddish.
The color of Azolla can change in different conditions. Azolla often turns reddish or brown in color when growing under intense sunlight or when the plant is stressed. The red tinge is due to the production of anthocyanins within the leaflets of the fern. Research has shown that anthocyanins may play a protective role in helping plants survive extreme temperatures & herbivory.
Is Azolla native to California?
According to sources, Azolla filculoides (Pacific Mosquito Fern) & Azolla Mexicana, are native to the warmer regions of North America and California. Other species of Azolla include – Azolla Carolina, Azolla nilotica, Azolla microphylla and Azolla pinnata. Not all of these can be found in CA. Some of the non-native species have been introduced to parts of North America. In recent years, the species Azolla pinnata (a native species to Asia, parts of Africa, & Australia) has been seen in California.
Azolla can grow quickly …. can it become invasive in a habitat?
We don’t often think of species that are native to an area as invasive. However, Azolla can have “boom-and-bust population cycles” that during certain seasons allow it to be dominate in a location. When nutrients like phosphorus are plentiful in the water & temperatures never get cold enough to cause Azolla to die back, its growth can quickly overtake water surfaces. Azolla may have some positives in that it can remove heavy metals like chromium, nickel, copper, zinc, & lead from the water. One of the negative effects of its surface covering ability is that water oxygen levels may become low with less surface area for oxygen to diffuse. Also, less light is able to pass through to the water below, making it difficult for other native aquatic plants and submerged animals that require light. Azolla can become a nuisance to humans if it clogs irrigation screens and pumps. It also has been reported that cattle won’t drink from water sources covered with Azolla.
Is Azolla native to California?
According to sources, Azolla filculoides (Pacific Mosquito Fern) & Azolla Mexicana, are native to the warmer regions of North America and California. Other species of Azolla include – Azolla Carolina, Azolla nilotica, Azolla microphylla and Azolla pinnata. Not all of these can be found in CA. Some of the non-native species have been introduced to parts of North America. In recent years, the species Azolla pinnata (a native species to Asia, parts of Africa, & Australia) has been seen in California.
Azolla can grow quickly …. can it become invasive in a habitat?
We don’t often think of species that are native to an area as invasive. However, Azolla can have “boom-and-bust population cycles” that during certain seasons allow it to be dominate in a location. When nutrients like phosphorus are plentiful in the water & temperatures never get cold enough to cause Azolla to die back, its growth can quickly overtake water surfaces. Azolla may have some positives in that it can remove heavy metals like chromium, nickel, copper, zinc, & lead from the water. One of the negative effects of its surface covering ability is that water oxygen levels may become low with less surface area for oxygen to diffuse. Also, less light is able to pass through to the water below, making it difficult for other native aquatic plants and submerged animals that require light. Azolla can become a nuisance to humans if it clogs irrigation screens and pumps. It also has been reported that cattle won’t drink from water sources covered with Azolla.
How does Azolla spread to other locations (native or non-native)?
Each individual Azolla plant multiplies by stem fragments and spores. Azolla can move into other aquatic habitats by natural means, transport by animal vectors, or by human actions. Fragments of the fern or its reproductive spores can naturally disperse through the water to other connected areas. Like duckweed, Azolla plants clinging to the feathers of waterfowl can be transferred to other unconnected waterways as the birds fly to new locations. Other animals like amphibians, reptiles, & mammals may also unintentionally transfer Azolla to new areas in this way. Azolla also has been intentionally introduced into new locations by humans. An example of this is, A. filiculoides which is used as a green manure for rice cultivation. Through this practice it has been brought to tropical regions worldwide.
How does Azolla spread to other locations (native or non-native)?
Each individual Azolla plant multiplies by stem fragments and spores. Azolla can move into other aquatic habitats by natural means, transport by animal vectors, or by human actions. Fragments of the fern or its reproductive spores can naturally disperse through the water to other connected areas. Like duckweed, Azolla plants clinging to the feathers of waterfowl can be transferred to other unconnected waterways as the birds fly to new locations. Other animals like amphibians, reptiles, & mammals may also unintentionally transfer Azolla to new areas in this way. Azolla also has been intentionally introduced into new locations by humans. An example of this is, A. filiculoides which is used as a green manure for rice cultivation. Through this practice it has been brought to tropical regions worldwide.
What Eats Azolla ?
Many of the herbivores that eat Azolla are generalists that eat a variety of other vegetation as well. We have observed Beavers scooping up green Azolla from the surface & eating it here in Rocklin, CA. Humans also use Azolla as a feed for livestock (ducks, pigs, chickens, etc.) since it is easy to grow & has a high protein content. In some Asian countries Azolla has been used as a fertilizer in rice fields for centuries. While the fields are flooded it crowds out other plants & when they are dry it decomposes adding nitrogen to the soil for the next rice crop. Some sources state that the rice production can be increased as much as 158%.
What Eats Azolla?
Many of the herbivores that eat Azolla are generalists that eat a variety of other vegetation as well. We have observed Beavers scooping up green Azolla from the surface & eating it here in Rocklin, CA. Humans also use Azolla as a feed for livestock (ducks, pigs, chickens, etc.) since it is easy to grow & has a high protein content. In some Asian countries Azolla has been used as a fertilizer in rice fields for centuries. While the fields are flooded it crowds out other plants & when they are dry it decomposes adding nitrogen to the soil for the next rice crop. Some sources state that the rice production can be increased as much as 158%.
There are a few specialist insect species that have evolved to eat just Azolla. These include four beetle species – the weevils Stenopelmus rufinasus (also known as the Water Fern Weevil) & S. brunneus and the flea beetles Pseudolampsis guttata and P. darwinii.
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Photo Credit – U.Schmidt, 2013 (licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license)
In 1948 Azolla filiculoides was intentionally introduced as a fishpond plant to South Africa where it proliferated. By the early 1980s it was thought to have invaded every river system there. To control it, Stenopelmus rufinasus was used as a biocontrol in Africa with success. In California however, native species Stenopelmus rufinasus has not always been very effective at limiting Azolla populations. It is speculated that temperature or other environmental factors may play a role in the success of the weevil.
There are a few specialist insect species that have evolved to eat just Azolla. These include four beetle species – the weevils Stenopelmus rufinasus (also known as the Water Fern Weevil) & S. brunneus and the flea beetles Pseudolampsis guttata and P. darwinii.
Photo Credit – U.Schmidt, 2013 (licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license)
In 1948 Azolla filiculoides was intentionally introduced as a fishpond plant to South Africa where it proliferated. By the early 1980s it was thought to have invaded every river system there. To control it Stenopelmus rufinasus was used as a biocontrol in Africa with success. In California however, native species Stenopelmus rufinasus has not always been very effective at limiting Azolla populations. It is speculated that temperature or other environmental factors may play a role in the success of the weevil.
Azolla’s effects upon California Lake Anza
An example of one habitat in CA transformed by Azolla’s growth is Lake Anza, a reservoir located within Tilden Regional Park of Berkeley. In 2022 an explosive growth of Azolla carpeted the surface of the lake changing the balance of species present.
Previously, before the Azolla take-over, the lake had a history of intermittent spikes of toxic blue-green algae blooms. In 2020, one such spike of this free-floating toxic algae caused the park to prohibit swimming in the lake. After the Azolla arrived, no toxic blue-green algae blooms have occurred thus far. It is thought that the massive growth of Azolla & its shading effect helped reduce light & nutrients that were available for growth of the toxic algae.
Growth of the toxic algae, that prefers warmer water, might have also been hindered by the cooler water that shade from the Azolla provided (despite the effects of reduced surface area for oxygen diffusion). Cooler water can carry more oxygen which also benefits fish such as the native Rainbow Trout within the Lake and other aquatic animals. In water where there is less oxygen, nutrients are more readily available to the toxic algae. As climate change gives us higher temperatures it is possible that Azolla’s shade may help in certain situations & ecosystems.
Outbreaks of Azolla like this one have also occurred inland, like this observation in May 2022 at Sailor’s Bar near Sacramento, CA along the American River – “Mosquito Fern” Abundant at Sailor Bar This Spring
Ecosystems are complicated – it is likely not so straight forward as classifying an explosive growth of Azolla as a good or bad thing.
Photo Credit – © 2022 Cynthia Powell CC-BY-NC 4.0
Ref Image on Calflora
Azolla’s effects upon California Lake Anza
An example of one habitat in CA transformed by Azolla’s growth is Lake Anza, a reservoir located within Tilden Regional Park of Berkeley. In 2022 an explosive growth of Azolla carpeted the surface of the lake changing the balance of species present.
Previously, before the Azolla take-over, the lake had a history of intermittent spikes of toxic blue-green algae blooms. In 2020, one such spike of this free-floating toxic algae caused the park to prohibit swimming in the lake. After the Azolla arrived, no toxic blue-green algae blooms have occurred thus far. It is thought that the massive growth of Azolla & its shading effect helped reduce light & nutrients that were available for growth of the toxic algae.
Growth of the toxic algae, that prefers warmer water, might have also been hindered by the cooler water that shade from the Azolla provided (despite the effects of reduced surface area for oxygen diffusion). Cooler water can carry more oxygen which also benefits fish such as the native Rainbow Trout within the Lake and other aquatic animals. In water where there is less oxygen, nutrients are more readily available to the toxic algae. As climate change gives us higher temperatures it is possible that Azolla’s shade may help in certain situations & ecosystems.
Photo Credit – © 2022 Cynthia Powell CC-BY-NC 4.0
Ref Image on Calflora
Outbreaks of Azolla like this one have also occurred inland, like this observation in May 2022 at Sailor’s Bar near Sacramento, CA along the American River – “Mosquito Fern” Abundant at Sailor Bar This Spring
Ecosystems are complicated – it is likely not so straight forward as classifying an explosive growth of Azolla as a good or bad thing.
GEOLOGICAL HISTORY & THE AZOLLA EVENT THEORY
Could Azolla be responsible for cooling the Earth’s climate ~ 49 million years ago?
GEOLOGICAL HISTORY & THE AZOLLA EVENT THEORY
Could Azolla be responsible for cooling the Earth’s climate ~ 49 million years ago?
According to scientific theory, about 49 million years ago, in the middle Eocene epoch, massive blooms of Azolla are thought to have cooled the climate of the Earth by removing large amounts of CO2 from the atmosphere. Azolla living in a small freshwater layer on the Arctic Ocean consumed CO2 from the air. When the Azolla eventually came in contact with the saltwater below, it died, sank down to the sea floor, & was trapped under sediment in effect reducing the amount of CO2 in the atmosphere. Over the period of 800,000 years this process of had the effect of cooling the earth’s climate.
According to scientific theory, about 49 million years ago, in the middle Eocene epoch, massive blooms of Azolla are thought to have cooled the climate of the Earth by removing large amounts of CO2 from the atmosphere. Azolla living in a small freshwater layer on the Arctic Ocean consumed CO2 from the air. When the Azolla eventually came in contact with the saltwater below, it died, sank down to the sea floor, & was trapped under sediment in effect reducing the amount of CO2 in the atmosphere. Over the period of 800,000 years this process of had the effect of cooling the earth’s climate.
References
- “Azolla in the Reservoir?” ANR Blogs, https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=57443 , Accessed 3 Aug. 2024.
- “Azolla.” CABI.Org, 18 Mar. 2024, www.cabi.org/invasivespecies/species/azolla/.
- Kwok, Iris. “Lake Anza Is Open to Swimmers – for Now – after Retreat of Squishy Fern and Toxic Algae.” Berkeleyside, 8 Aug. 2023, www.berkeleyside.org/2023/08/07/lake-anza-swimming-toxic-algae-bloom-azolla-fern-east-bay-regional-park-district#:~:text=Lake%20Anza%20hadn’t%20been,such%20spike%20in%20toxic%20cyanobacteria.
- “Saccounty News.” SacCounty News, https://www.saccounty.gov/news/latest-news/Pages/Mosquito-Fern-Abundant-at-Sailor-Bar-This-Spring.aspx#:~:text=Both%20species%20of%20Azolla%20are,seem%20like%20they%20are%20invasive. Accessed 3 Aug. 2024.
- Song, Michael J., et al. “First Record of the Invasive Azolla Pinnata Subsp. Pinnata (Salviniaceae) in California.” BioOne Complete, The American Fern Society, https://bioone.org/journals/american-fern-journal/volume-113/issue-1/0002-8444-113.1.56/First-Record-of-the-invasive-Azolla-pinnata-subsp-pinnata-Salviniaceae/10.1640/0002-8444-113.1.56.short Accessed 8 Aug. 2024.
- Author links open overlay panelA.J. McConnachie a, et al. “Field Assessment of a Frond-Feeding Weevil, a Successful Biological Control Agent of Red Waterfern, Azolla Filiculoides, in Southern Africa.” Biological Control, Academic Press, 20 Oct. 2003, www.sciencedirect.com/science/article/abs/pii/S1049964403001853?via%3Dihub.
- “Azolla.” Wikipedia, Wikimedia Foundation, 8 July 2024, https://en.wikipedia.org/wiki/Azolla.
- “Azolla Event.” Wikipedia, Wikimedia Foundation, 13 Feb. 2024, https://en.wikipedia.org/wiki/Azolla_event