Sea creatures pollinate marine plants and algae, surprising scientists (2022)

ByLina Zeldovich

Published August 8, 2022

8 min read

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About a decade ago, Vivianne Solis-Weiss, a marine biologist at Universidad Nacional Autónoma de México who studies marine worms, talked to a colleague studying seagrasses, flowering plants that grow in the ocean.

“‘Every time we gather the flowers, we see these small animals all over them,’” she recalls her colleague telling her. Both wondered why these little worms and tiny shrimp-like crustaceans would gather there. Could they be pollinating the plants—the marine equivalent of bees and butterflies?

Solis-Weiss and her colleagues hypothesized that the creatures might indeed play a role in ocean pollination and outlined their idea in a study, which appeared in the small journal Inter-Research Science Publisher in 2012.

“It was very hard to publish that first paper, because no one would believe us,” she recalls.

The role of pollinators on Earth is well-established. Hundreds of thousands of flowering species depend on animals and insects to procreate. The plants provide nectar or the promise of something to eat, and the pollinators facilitate the plants’ sexual reproduction. But until recently, it was believed to be a terrestrial-only phenomenon that didn’t exist in the ocean.

“There is a dogma that in marine environments all the fertilization is done by water movements,” says Emma Lavaut, a marine biologist at Roscoff Marine Station of Sorbonne University in France, who studies Gracilaria gracilis, a seaweed commonly called red algae that grows in coastal rock pools. Indeed, in many marine organisms, males and females release their eggs and sperm into the water, letting the currents mix and fertilize them.

Yet, in the past few years, new evidence has emerged suggesting that the ocean has its own pollinators. These creatures can be likened to the “bees of the sea,” and they may be more common than we imagine. As scientists learn more about their symbiotic relationships, it changes how they think about the evolution of all involved—algae, plants, insects, and crustaceans. It also highlights the complexity of these mutually beneficial relationships.

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Grass and seaweed mysteries

To prove their hypothesis, Solis-Weiss’s team set up research fields of seagrass Thalassia testudinumon the ocean shore and in aquariums, capturing the pollination process with photos and videos. Every sunset when the male flowers of T. testudinumopened, worms and other invertebrates would swarm among them, covering themselves in pollen.

“We made experiments to show that they will go to forage in the masculine flowers, get the pollen, which sticks to their body, and then go to the feminine flowers and leave the pollen there,” Solis-Weiss says. In 2016, the team published these findings, along with pictures of marine worms covered in pollen in the journal Nature—the first ever study to demonstrate pollination in the sea.

Lavaut was next to observe a similar phenomenon while working on her PhD thesis about the G. gracilis’ reproductive mysteries. Rather than spewing its eggs into the waves like many other ocean inhabitants,the female alga keeps them inside its funnel-shaped filaments called thalli. The males release the sperm, but the tiny cells don’t have the tails to swim to the female plants and get inside the filaments.

That seeming disadvantage doesn’t affect the reproductive success of the seaweed: The taxonomic group to which red algae belong evolved around 1 billion years ago. Lavaut and her advisor Myriam Valero, a population geneticist at the French national research agency CNRS, wanted to understand how these organisms reproduce.

Over the years of studying the algae in the tidepools around Europe, Valero noticed that most fertilization happens at low tide, when there is little water. At that time, swarms of little isopods called Idotea balthica—crustaceans that look like a cross between a shrimp and a pill bug—swim within the algae. Valero and her team wondered if they were transporting the sperm on their bodies.

To test that idea, the team used virgin G. gracilisthathas never been fertilized before and didn’t have any fruiting structures called cystocarps. The scientists placed male and female plants inside multiple aquariums and added 20 crustaceans to some but not others. When cystocarps developed, the aquariums with the creatures had 20 times more of them.

“I was surprised by the fact that there was much more fertilization,” Lavaut says. The team also gathered crustaceans that swam in the tanks with the male alga for some time, then releasing them into tanks with virgin female plants, which also increased the number of cystocarps. Under the microscope, the isopods were covered in tiny specks of sperm just like marine worms in Solis-Weiss study. Lavaut’s group reported its findings on July 28 in the journal Science.

In this case, both organisms are helping each other. Algae provide shelter for the isopods, but also food in the form of an algal biofilm that grows to coat G. gracilis. That cleanup helps these red algae photosynthesize.

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“If there’s too much [biofilm] growth, the red algae start to die,” Lavaut says—and the isopods help keep it clean.

Ancient roots

But while two teams described a seemingly similar phenomenon, evolutionary biologists and pollination ecologists point out that the two studies have major differences.

Seaweed and seagrass may sound similar, but they are two very different organisms with divergent evolutionary trajectories. Seagrasses have only been around for about 130 million years, says Jeff Ollerton, an ecologist who studies pollination at the Kunming Institute of Botany at the Chinese Academy of Sciences who was not involved in either study.

Seagrasses evolved from terrestrial plants that returned to sea yet retained some of their land features, such as flowering. And, apparently, relying on animals for pollination.

“It’s so interesting to see how they found in the water different kinds of animals to replace bees and butterflies,” says Solis-Weiss—which she means in a figurative, not literal sense.

In comparison, seaweeds are only distantly related to plants, and are neither plants nor animals, but their own thing—a type of algae, Ollerton explains. They are ancient organisms that evolved eons before plants left the ocean and began to grow on land. That means that pollination may predate plants, says Zong-Xin Ren, botanist and pollination ecologist also with the Kunming Institute.

“This finding totally changed our idea [of] what is pollination,” he says. “We may even redefine what pollination is.”

Save the isopods

This discovery prompted Ren and Ollerton to write a perspective paperDid pollination exist before plants?—in which they reflect on the significance of such mutually beneficial relationships between animals and photosynthetic organisms stretching back much further in evolutionary history than thought.

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Such relationships between species are what allows ecosystems to function, and “to understand when such interaction[s] began will greatly increase our understanding of the original biodiversity,” Ren says.

“We know so little about our world, so little about what’s happening on land and even less about what’s happening in the water,” he adds. “The paper gave us the tip of the iceberg.”

The new research suggests that the important and previously unknown relationships between animals and aquatic plants and algae could make them more vulnerable. In the case of red algae, for example, most pollination takes place in shallow tide pools, where the delicate dance between animals and those they pollinate could be disrupted by pollution, climate change, and development.

On land, bees are under threat from pesticides and other toxins, much of which washes into the sea. Will the sea’s bees find themselves in a similar peril one day? On his blog, Ollerton cautions about this possibility.

“In the same way that ‘Save the Bees’ has been a rallying call for conserving interactions between species on land,” he writes, “we may soon hear this message echoed in ‘Save the Isopods.’”

Looking forward, the researchers are excited to see if more examples of pollination can be found in nature—and they suspect there will be.

“There are no doubt many more revelations awaiting the careful observer,” Ollerton and Ren write.


How do marine plants pollinate? ›

Pollen transport by water-flow (hydrophily) is a typical, and almost exclusive, adaptation of plants to life in the marine environment. It is thought that, unlike terrestrial environments, animals are not involved in pollination in the sea.

Do underwater plants get pollinated? ›

Underwater invertebrates can ferry pollen between flowers, in the same way that bees and other animals pollinate plants on land.

How do algae pollinate? ›

Red algae benefit from the pollination by crustacean

Upon contact with a female alga, the sperm attaches itself to its reproductive structure and fertilizes the eggs. The researchers are now curious to find out if other algal species are also pollinated with the help of animals.

How does seaweed pollinate? ›

As isopods scuttle along a male seaweed stalk, they are bombarded by spermatia, which are coated in a tacky, mucuslike substance. Like a powder-coated bee spreading pollen from plant to plant, isopods spread spermatia throughout a tide pool as they travel between seaweed clumps.

How do marine plants reproduce? ›

Reproduction. Although most aquatic angiosperms can reproduce by flowering and setting seeds, many have also evolved to have extensive asexual reproduction by means of rhizomes, turions, and fragments in general.

How do aquatic animals undergo pollination? ›

Many species overcome this hurdle by thrusting their flowers up and out of the water where there are far more pollen vectors. Others rely on water currents and a little bit of chance. For aquatic plants whose flowers open under water, water pollination, or "hydrophily", has long been the only proposed mechanism.

Which plant is pollinated by water? ›

Water pollinated plants are Vallisneria, water lily, Zostera.

Why are water plants get pollinated even if they are in the middle of a pond? ›

Most aquatic plants have flowers that grow into the air, where they are pollinated by insects. Plants that are water-pollinated usually have small, inconspicuous male flowers that release lots of pollen grains that drift in the water where they are caught by the large, feathery stigmas of female flowers.

Is algae water pollinated? ›

Once thought to be a land-only phenomenon, pollination may have existed in the ocean millions of years before terrestrial plants appeared.

What is the importance of pollination? ›

It is an essential ecological survival function. Without pollinators, the human race and all of earth's terrestrial ecosystems would not survive. Of the 1,400 crop plants grown around the world, i.e., those that produce all of our food and plant-based industrial products, almost 80% require pollination by animals.

Why are pollinators important in the reproduction of plants? ›

Pollination is an essential part of plant reproduction. Pollen from a flower's anthers (the male part of the plant) rubs or drops onto a pollinator. The pollinator then take this pollen to another flower, where the pollen sticks to the stigma (the female part). The fertilized flower later yields fruit and seeds.

Does pollination help photosynthesis? ›

Increasing absorption of CO2 and other harmful to humans, wild life and animals emissions via increased pollination of flowering trees, plants and flowers which in turn increases the numbers of trees and via photosynthesis increased absorption of emissions and increased production of atmospheric oxygen.

How do plants depend on animals for reproduction? ›

Animals help plants by helping pollinate flowers or by dispersing seed. They also help supply nutrients when they die and decompose.

Are there bees in the ocean? ›

For the first time, researchers have found evidence that underwater ecosystems have pollinators that perform the same task as bees on land. Just like their terrestrial cousins, grasses under the sea shed pollen to sexually reproduce.

What is cross pollination short answer? ›

Cross-pollination is the process of applying pollen from one flower to the pistils of another flower. Pollination occurs in nature with the help of insects and wind.

What are plants that grow in water called? ›

Aquatic plants are the plants which are adapted to grow in water. Plants like lotus and hydrilla are examples of aquatic plants.

Is marine algae a plant? ›

Some can grow to up to 60 metres in length. Seaweeds include members of the red, brown and green algae. They are members of the kingdom Protista meaning they are not Plants. They do not have the vascular system (internal transport system) of plants and do not have roots, stems, leaves and flowers or cones.

Do underwater flowers exist? ›

Sea anemones, though considered the flowers of the sea for their gracefully flowing tentacles and array of colors, are not plants at all. The tentacled organisms are meat-eating animals that typically attach themselves to the seafloor or coral reefs.

What is pollination by animals called? ›

Pollination, which occurs through the means of animals, is known as zoophily.

In which of the following aquatic plant pollination takes place by insect? ›

Majority of floating aquatic plants are insect or wind pollinated.

Do animals help in pollination? ›

In general, pollination by animals occurs after they reach inside the flowers for nectar. While feeding on the nectar, the animal rubs or touches the stamens and is covered in pollen. Some of this pollen will be deposited on the stigma of the next flower it visits, pollinating the flower.

How are marine angiosperms pollinated? ›

The marine angiosperms have adapted to a hydrophilous pollination mode, in which pollen is released and captured underwater.

How are the flowers of sea grasses adapted for pollination? ›

<br> In sea grasses show hydrophilly type of pollination here the female flowers are submerged in water to receive pollen grains for pollination inside water. pollen grains are long, ribbon like structures to be carried passively inside the water.

How is water hyacinth pollinated? ›

The flowers of water hyacinth and water lily emerge above the level of water and are pollinated by insects or wind.

Why do plants flower underwater? ›

Considering the purpose of flowers, you might wonder how plants grow in water. The truth is that many aquatic plants grow above the surface of the water. Usually, their roots are submerged, but the flower remains above the surface. This gives water plants a better chance to pollinate.

Is water lily water pollinated? ›

In aquatic plants such as water hyacinth and water lily, pollination is by water.

How do plants depend on animals for reproduction? ›

Animals help plants by helping pollinate flowers or by dispersing seed. They also help supply nutrients when they die and decompose.

How do wind help in pollination? ›

Wind pollinating plants release billions of pollen grains into the air so that a lucky few will hit their targets on other plants. Many of the world's most important crop plants are wind-pollinated.

How some plants are adapted for achieving pollination through wind? ›

They often possess well-exposed stamens so that the pollens are easily dispersed into wind currents, and large, often-feathey sligma to easily trap air-borne pollen grains. <br> Wind pollinated flowers often have a single ovule in each ovary and numerous flowers packed into an inflorescence.

What are the characters of water pollinated flowers? ›

  • Water pollinated plants are usually aquatic.
  • They produce a large number of pollen grains as most of them get lost in the water flow and very few are able to reach the stigma.
  • The stigmas of the female flower are usually above the water and are large and feathery to catch the pollen grains.

How does seagrass reproduce? ›

Most seagrasses reproduce by pollination - the pollen is transported to other plants by water. The roots and horizontal stems (rhizomes), often buried in sand or mud, anchor the grasses and absorb nutrients. Leaves, usually green, are produced on vertical branches and also absorb nutrients.

Which aquatic plant is pollinated by insect? ›

ii) Water lily and water hyacinth are pollinated by insects or wind.

Which pollen grains are long and ribbon like? ›

Zostera is a submerged sea-grass which releases long, ribbon-like pollen grains underwater. The pollen grains are carried passively by water and ultimately reach female flowers.

Why are water plants get pollinated even if they are in the middle of a pond? ›

Most aquatic plants have flowers that grow into the air, where they are pollinated by insects. Plants that are water-pollinated usually have small, inconspicuous male flowers that release lots of pollen grains that drift in the water where they are caught by the large, feathery stigmas of female flowers.

Can you put a peace lily in a fish tank? ›

Peace lilies grows beautifully in aquariums — making them suitable for aquaponics systems. This peace lily plant has been living in my aquariums for over 15 years. It helps to keep the water clean and reduce algae growth. Roots provide shelter for fish babies and serve as a home for hatching snails.

Can I put flowers in my fish tank? ›

Your plants will grow and your fish will swim around, but for the most part your aquarium will look the same every day. Adding freshly cut flowers to your aquascape allows you to change your layout weekly. Just think of how the bright scales of your fish would accent the delicate petals of the flowers.


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