These Pollinating Crustaceans Are the Bees of the Sea

Small, bug-like creatures can transfer pollen to red seaweed underwater

Crustacean
The crustacean Idotea balthica can pollinate red seaweed. Wilfried Thomas / Station Biologique de Roscoff, CNRS, SU, Roscoff, France

Bees, butterflies, moths, hummingbirds and other nectar-seeking wildlife are often heralded for the vital role they play in pollinating flowering plants on land.

Now, there’s a new creature to add to the very important pollinator list, one that helps plants flourish in a surprising place: underwater.

Scientists have discovered that a small, bug-like crustacean called Idotea balthica can pollinate red seaweed, a type of algae often found growing in tide pools. The findings, published Thursday in the journal Science, add to a small but growing body of evidence that raises questions about whether animal-mediated pollination may have first evolved underwater, instead of on land. It’s also possible that pollination evolved in separate instances, underwater and on land.

“Until recently, fertilization with the help of animals was believed to have emerged among plants when they moved ashore 450 million years ago,” says Myriam Valero, a biologist at Sorbonne University and one of the study’s authors, to NewScientist’s Carissa Wong. “Red algae arose over 800 million years ago and their fertilization via animal intermediaries may long predate the origin of pollination on land. However, we cannot rule out that different animal-mediated fertilization mechanisms evolved independently and repeatedly in terrestrial and marine environments.”

After scientists discovered in 2016 that zooplankton can pollinate seagrass in the Caribbean, Valero got curious about whether the same phenomenon might be happening with the red seaweed Gracilaria gracilis she studies.

To answer that question, Valero and other collaborators situated one male and one female red seaweed plant about six inches apart in aquariums. Next, they added 20 of the I. balthica crustaceans to the tanks. For comparison, they also set up aquariums containing a male and female plant but did not add the crustaceans.

They found that there were 20 times more fertilization events in the tanks with the crustaceans than those without. The scientists also gathered crustaceans that had spent time in aquariums with reproductive male seaweed plants and relocated them to tanks containing unfertilized female plants. This, too, produced high rates of fertilization. Looking at the crustaceans under a microscope, they also discovered spermatia—the seaweed’s version of sperm—stuck to their bodies.

Spermatia
The crustaceans had spermatia on their bodies. Sebastien Colin / Max Planck Institute for Biology, Tübingen, Germany; Station Biologique de Roscoff, CNRS, SU, Roscoff, France

The researchers suspect that the crustaceans are getting something out of the deal, too. Namely, a safe place to hide from predators and a source of food in the form of small, single-celled alga that grow on red seaweed plants, reports Erik Stokstad for Science.

The study, which is the first to document an animal fertilizing seaweed, “really shakes up our understanding of how seaweeds reproduce,” Jeff Ollerton, an ecological scientist and the author of Pollinators and Pollination: Nature and Society who was not involved with the study, tells the New York Times’ Annie Roth.

“This type of interaction may have been going on long before plants ever evolved and using a third party for reproduction may have much deeper roots than we ever realized,” he says.