Scientists have long assumed that plants that live underwater either self pollinate or grow via cloning. After all, there are no bees in the sea—and the motion of the water itself was once thought to be sufficient to move sea pollen from point A to point B. But it turns out that water is only half the story, reports Emily Benson for New Scientist. Scientists have now discovered that tiny invertebrates also take pollen from place to place underwater, visiting flowers and spreading their pollen like bees.
The discovery, recently published in the journal Nature Communications, could change the way scientists think of oceans. Brigitta van Tussenbroek is a marine botanist at the National Autonomous University of Mexico’s marine science institute who studies macrophytes—aquatic plants—in beds of seagrass. A few years ago, she was studying the plants in a lagoon in the Mexican Caribbean when she observed tiny invertebrates visiting male and female flowers. Upon further observation, van Tussenbroek and her colleagues suspected that these little visitors had another purpose: pollination.
The team took to the lab to learn more. There, they used aquariums containing male and female flowers of Thalassia testudinum, or turtle grass, some of which had a few pollen grains already attached, and poured in seawater that contained about 500 sea creatures (mainly crustacean larvae) per liter. Then they filmed what they saw. Within 15 minutes of pouring in the water, pollen grains began to appear on the female flowers. In comparison, tanks without the crustacean-containing seawater didn’t result in the same phenomenon.
Okay, so bee-like creatures could be responsible for part of the pollination under the sea. But did van Tussenbroek and her team just discover a previously unknown process that makes the entire underwater ecosystem grow? The jury is still out: It’s not clear yet whether the tiny, pollen-carrying crustaceans are a substitute for water in the case of turtle grass or if they’re the only way pollination occurs. Scientists also don’t yet know if other species of grass rely on crustaceans for the same service.
Nevertheless, the experimental results could be a sign that “sea bees” are buzzing around underwater, making things grow—and given global threats to sea grass, that could be a very good thing. Sea grass plays a vital role in Earth’s ecosystem, sequestering carbon and allowing biodiversity to flourish. But it's in trouble: Earth loses about 1.5 percent of its sea grass cover every year, and over a quarter of all historic sea grass meadows have been destroyed. Scientists may have only just discovered so-called “sea bees,” but already the stakes for their survival are high.