Meet the tiny critter that pollinates seaweed like a bumblebee

Science It’s one of the only sea creatures known to carry sperm on its body. by Jennifer Walter July 28, 2022 © Wilfried Thomas @Station Biologique de Roscoff, CNRS, SU, Roscoff, France

Demitry Skorinoff / 500px/500px/Getty Images Most plants couldn’t survive without bees, thanks to their ability to pollinate and help stationary organisms reproduce.

But for seaweed, the story is a little different. Seaweed is not a true plant, but algae. Most species of algae are thought to reproduce asexually or rely on currents in the ocean to spread mature sex cells, known as gametes. Shutterstock

© Wilfried Thomas @Station Biologique de Roscoff, CNRS, SU, Roscoff, France Meet the tiny isopod Idotea balthica. It has an affinity for the red algae Gracilaria gracilis, which grows in bunches of scraggly seaweed, creating the perfect shelter from predators.

I. balthica doesn’t eat the seaweed. But it’s an extremely common presence on G. gracilis, so the researchers wondered if it could potentially be aiding the seaweed in a mutual benefit. © Wilfried Thomas @Station Biologique de Roscoff, CNRS, SU, Roscoff, France

And if so, was I. balthica directly carrying gametes on its body, or indirectly creating currents to push them through the water?

Shutterstock For the study, they designed two experiments to see if the isopods moved gametes from male to female samples of seaweed.

Here are the isopods bumbling between male and female seaweed samples during an experiment.

© Sebastien Colin; Max Planck Institute for Biology, Tübingen, Germany; Station Biologique de Roscoff, CNRS, SU, Roscoff, France It turns out I. balthica does have the ability to transport gametes between seaweed in a similar way to how a bumblebee carries a plant’s pollen on its fuzzy legs.

The green flecks show clusters of gametes from the male seaweed on the hair-like bristles of I. baltica’s legs.

Since algae like G. gracilis predate plants by millions of years, it’s possible that pollinators might be older than plants themselves.

There could have been a different seaweed pollinator that came before I. baltica, researchers suggest in a related Science commentary.

Shutterstock The isopod didn’t appear until far after Gracilaria algae cropped up in Earth’s oceans.

But the isopod and the seaweed have a beneficial relationship that probably goes back millions of years — even if scientists weren’t aware of it until now.