Like Sea Bees, These Crustaceans Pollinate Seaweed

By Anne Roth

Gone are birds and bees, other pollinators on planet Earth, and live in the ocean. In a study published Thursday in Science, scientists found that a small crustacean, Idotia balthica, plays the role of a pollinator for this type of seaweed. They do this by inadvertently collecting the algae’s sticky sperm, which is the pollen equivalent, on their bodies and whisking them around as they move from ringworm to ringworm in search of food and shelter. This is the first time an animal has been observed feeding on algae. The discovery not only expands the range of species using this breeding strategy, but also raises the question of whether they first evolved on land or in the sea.

It has long been believed that animals only pollinate plants on Earth. However, in 2016 scientists found that zooplankton pollinated Thalassia testudinum, a type of seaweed found in the Caribbean. Seaweeds are the only flowering plants that grow in marine environments, but they are still closely related to land plants. On the other hand, seaweed is not closely related to land plants, although technically it is cultivated alone.

It was found that Thalassia testudinum was pollinated by animals when scientists observed high densities of marine invertebrates visiting seaweed flowers. Shortly after this discovery, population geneticist Myriam Valero of the Sorbonne University in France noticed something similar was happening among the red algae he was studying. The species of seaweed they studied, Gracilaria gracilis, appears to be common in invertebrates, particularly the isopod species Idotia balthica. Because Gracilaria gracilis produces sperm, which, like pollen, cannot move on its own, Dr. Valero wondered whether isopods played a role in the dispersal of sperm. Previous studies have shown that Gracilaria gracilis spermatozoa are dispersed by ocean currents, but because of the abundance of these spermatozoa in calm coastal rock pools, Dr. Valero suspected another diffusion mechanism.

To test his hypothesis, Dr. Valero and Emma Lafot, graduate students at the Sorbonne, raised males and females of Gracilaria gracilis and placed them six inches apart in seawater tanks. Half of the reservoir is inhabited by small crustaceans, while the rest are not. At the end of their experiment, they found that fertilization occurred about 20 times in isosceles tanks compared to tanks without them.

In a later experiment, the researchers took crustaceans that had spent time in tanks with breeding males of Gracilaria gracilis and transferred them to tanks with unfertilized female algae. They found that it also resulted in higher fertilization rates. He examined the isosceles under the microscope and found that almost every part of his body had sperm attached to it.

Researchers believe that isopods have a relationship with seaweeds. Isopods provide food in the form of a type of microscopic algae that grow on their surface as well as shelter. In turn, isopods help in the fertilization of algae.

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