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.

FAQs

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 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 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.

How is seagrass pollinated? ›

Sexual Reproduction: Seagrasses reproduce sexually like terrestrial grasses, but pollination for seagrasses is completed with the help of water. Male seagrass flowers release pollen from structures called stamens into the water.

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.

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.

How do underwater 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 seagrasses 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.

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.

Is kelp a seaweed? ›

Kelp is a large, brown seaweed that typically grows in shallow saltwater near coastal areas around the world. You can eat it raw, cooked, as a powder, and it's included in a number of supplements.

Which is two plant examples of pollination by water? ›

Water pollinated plants are Vallisneria, water lily, Zostera.

How is pollination achieved in the water lily? ›

In water lily, pollination takes place through wind or insect as the female flower emerges above the surface of water.

What is pollination by animals called? ›

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

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.

Is water lily water pollinated? ›

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

What is surface pollination? ›

In the surface mode of pollination, pollen rafts or 'search vehicles' which superficially resemble snowflakes, form at low tide and are transported on the surface of the sea by winds and water currents. Some of the search vehicles collide with the floating female stigmas, effecting pollination.

What is pollination by water called? ›

Water pollinated plants are aquatic. Pollen floats on the water's surface drifting until it contacts flowers. This is called surface hydrophily, but is relatively rare (only 2% of pollination is hydrophily). This water-aided pollination occurs in waterweeds and pondweeds.

In which aquatic plant pollination takes place by insect? ›

Final answer: In water hyacinth and water lily pollination takes place by insects and wind respectively.

Which aquatic plant is pollinated by insect? ›

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

Is water lily poisonous? ›

All water lilies are poisonous and contain an alkaloid called nupharin in almost all of their parts, with the exception of the seeds and in some species, the tubers.

Are there any blue aquatic plants? ›

Deep Blue Buce Plant (Bucephalandra sp. “Deep Blue”) is a striking variant of the extremely popular Bucephalandra group. It is a very hardy plant that can be grown emersed or submerged in the aquarium, terrarium, and paludarium. It requires only low to moderate lighting and can thrive in a variety of water parameters.

What are macrophytes? ›

Macrophytes are aquatic plants growing in or near water. They may be either emergent (i.e., with upright portions above the water surface), submerged or floating. Examples of macrophytes include cattails, hydrilla, water hyacinth and duckweed. Macrophyte sampling during the 2012 National Lakes Assessment in Colorado.

Do underwater plants produce oxygen? ›

The primary source of oxygen for a pond is from microscopic algae (phytoplankton) or submerged plants. In the presence of sunlight, these produce oxygen through photosynthesis and release this oxygen into the pond water.

How do plants underwater survive without sunlight? ›

This process is called photosynthesis. In the deep ocean, many hundreds of meters away from the sun's rays, another process is taking place: chemosynthesis. Tiny microbes use chemical energy instead of light to combine water and carbon dioxide to make sugar.

How do underwater plants get CO2? ›

But for plants that live completely submerged in water, CO2 is limited and many of these plants have developed a mechanism to tap into other carbon sources. In this case, they extract it from bicarbonate — a naturally occurring mineral that comes from the weathering of soils and rocks.

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 sea plants reproduce? ›

Seagrasses can reproduce sexually or asexually. They are flowering plants that produce seeds. Pollen is carried through the water to fertilize female flowers. Seagrasses can also send out rhizome roots that can sprout new growth, so a single plant is capable of producing an entire underwater meadow.

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.

How does seaweed breed? ›

Seaweed is a plant, but does not reproduce like most plants do on land, with flowers and pollen. Seaweed is more like a fern that reproduces by means of spores. Alexander Ebbing studies how these spores (gametophytes) can be controlled using various (a)biotic factors, further domesticating the species.

Can seaweed reproduce asexually? ›

Seaweed reproduction can involve either exclusively sexual or asexual phases, while some species display an alternation of generations that involves both in succession.

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.

How do seagrass reproduce asexually? ›

Asexual reproduction method: Like land grass, seagrass' roots connect with one another underneath the seabed like roots, also called rhizomes. Rhizomes can spread widely under the seabed and push shoots above the seabed. This means all young seagrass share the same body and genetic materials.

How do plants survive in the ocean? ›

TL;DR: Ocean plants have developed adaptations such as the ability to absorb nutrients from water, the ability to float and the ability to anchor themselves to rocks on the ocean floor in order to thrive in their challenging environment.

How does sea grass grow? ›

Seagrass are flowering plants that grow entirely underwater

The depth at which seagrass are found is limited by water clarity, which determines the amount of light reaching the plant. Light is required for the plants to make food through photosynthesis.

Is water lily water pollinated? ›

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

How does seagrass adapt? ›

Seagrasses are resistant to erosion by waves and tidal currents, due to well-developed rhizomes and numerous, fleshy roots that anchor into the substrate. The supple leaves are better resistant to water movement than stiff leaves.

Why all Hydrophytes are not pollinated by water? ›

All hydrophilous plants are hydrophytes as they require water in close proximity for pollination to occur. However, in majority of hydrophytes, like water hyacinth and water lily, flowers lie above the level of water and thus are pollinated by insects or wind as in most of the land plants.

Which aquatic plant is pollinated by insect? ›

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

In which aquatic plant pollination takes place by insect? ›

Final answer: In water hyacinth and water lily pollination takes place by insects and wind respectively.

How are lilies pollinated? ›

Pollination Process

Their bright colors call in butterflies and bees, the lily's primary pollination assistants. Insect helpers jump from flower to flower, carrying pollen from the stamens to the pistils. Pollen attaches to the sticky stigma and then works its way down the style and into the ovary.

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