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Like Bees of the Seas, These Crustaceans Pollinate Seaweed


Move over birds and bees, there may be one other pollinator on planet Earth, and it lives in the ocean.

In a study, published Thursday within the journal Science, scientists found that a tiny crustacean, Idotea balthica, played the role of pollinator for a species of seaweed. They do that by inadvertently collecting the algae’s sticky spermatia, its equivalent of pollen, on their bodies and sprinkling it around as they move from frond to frond searching for food and shelter.

That is the primary time an animal has been observed fertilizing an algae. This discovery not only extends the scope of species that use this reproductive strategy, it also raises questions on whether it first evolved on land or in the ocean.

It was long thought that animals only pollinated plants on land. Nonetheless, in 2016 scientists discovered that zooplankton pollinate Thalassia testudinum, a sea grass species present in the Caribbean. Sea grasses are the one flowering plants that grow in marine environments, but they continue to be closely related to terrestrial plants. Seaweeds alternatively, while technically plants themselves, will not be closely related to terrestrial plants.

The invention that Thalassia testudinum was pollinated by animals was made after scientists noticed an unusually high density of marine invertebrates visiting sea grass flowers. Shortly after this discovery, Myriam Valero, a population geneticist at Sorbonne University in France, observed something similar happening among the many red algae she was studying.

The seaweed species she was studying, Gracilaria gracilis, at all times seemed popular with invertebrates, specifically the isopod species Idotea balthica. Because Gracilaria gracilis produce spermatia that, like pollen grains, cannot move on their very own, Dr. Valero wondered if the isopods is likely to be playing a job within the spermatia’s dispersal. Earlier studies suggested that the spermatia of Gracilaria gracilis were dispersed by ocean currents, but given their abundance in calm coastal rock pools, Dr. Valero suspected one other dispersal mechanism was at play.

To check her hypothesis, Dr. Valero and Emma Lavaut, a graduate student at Sorbonne, grew female and male Gracilaria gracilis and placed them six inches apart in seawater tanks. Half the tanks were populated with the tiny crustaceans, while the others weren’t. At the tip of their experiment, they found that fertilization occurred around 20 times as much within the tanks with the isopods than within the tanks without them.

In a subsequent experiment, the researchers took crustaceans that had hung out in tanks with reproductive male Gracilaria gracilis and transferred them to tanks with unfertilized female algae. They found that doing so also resulted in high rates of fertilization. They examined the isopods under a microscope and located that that they had spermatia stuck to almost every a part of their bodies.

The researchers imagine the isopods have a mutualistic relationship with the seaweed. The algae provides the isopods with food in the shape of a species of microalgae that grow on its surface in addition to shelter. In exchange, the isopods help fertilize the algae.

“That is such a profoundly fascinating study that actually shakes up our understanding of how seaweeds reproduce,” said Jeff Ollerton, a visiting professor on the Kunming Institute of Botany in China who was not involved with the study but co-wrote a perspective article that accompanied the study in Science on Thursday. “One of these interaction can have been happening long before plants ever evolved and using a 3rd party for copy can have much deeper roots than we ever realized — if you happen to’ll excuse the pun.”

The group to which the Gracilaria gracilis belongs is assumed to have evolved around 500 million years before the primary plants appeared on land. Although isopods only hit the scene 300 million years ago, it is feasible that before their arrival, there have been red seaweeds that relied on another now-extinct marine invertebrates to “pollinate” them.

“It could be possible that the connection between seaweed and animals predates the evolution of the animal-plant relationship,” said Dr. Valero, who acknowledged that this hypothesis couldn’t yet be proven. One other possibility, she said, was that animal-mediated fertilization strategies evolved independently and repeatedly within the terrestrial and marine environment.

Dr. Valero added that it was vital to search out out whether other red algae species relied on marine animals for fertilization since it may very well be critical to the upkeep of biodiversity in our oceans. While scientists are documenting how pollution and climate change affect the connection between plants and pollinators on land, now we have no idea how these forces impact the connection between algae and their “pollinators” within the ocean.

In the approaching years, Dr. Valero hopes to be certainly one of the scientists to figure this out.

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