Unlikely Pollinators: Experts Observed Animal-Mediated Fertilization of Seaweed for the First Time

For the first time, experts have evidence of animal-driven "pollination" of seaweed. Red algae were initially believed to reproduce without the help of other living creatures, but recent findings show how small crustaceans help transport sex cells of male and female algae, similar to bees pollinating flowers and fruits.

Crustaceans Pollinating Seaweed: A First

(Photo: Sean Gallup/Getty Image)
HELGOLAND, GERMANY - AUGUST 03: A live adult female European lobster (Homarus gammarus) lies on the floor for a photo at the Helgoland Biological Institute (Biologische Anstalt Helgoland), part of the Alfred Wegener Institute for Polar and Marine Research, on August 3, 2013, on Helgoland Island, Germany. Scientists released 415 one-year-old lobsters into the North Sea later in the day to repopulate the lobster population around Helgoland (also called Heligoland). In the 19th century, local fishers caught up to 80,000 lobsters a year in the surrounding waters, combined with the heavy allied bombing of the island during and after World War II and other environmental factors decimated the lobster population.

In the study published in the journal Science, titled "Pollinators of the sea: A discovery of animal-mediated fertilization in seaweed," researchers note that both crustaceans and red algae belong to an ancient group, far older than land plants, which raises the possibility that the first pollination occurred in the ocean, hundreds of millions of years before what we believe.

Pollination is described as the process of transferring male sex cells - pollen, to female flowers on land. But in 2016, researchers discovered that marine invertebrates "pollinate" seagrass flowers by feeding on and moving between the pollen-masses of seagrasses, a descendant of land plants. But nothing of the sort has been documented in algae.

Like other red algae, Gracilaria gracilis does not have free-swimming male sex cells. Initially, it was believed that the sex cells were dispersed to female alga via water flow, similar to how wind spreads pollen to fertilize some land plants.

In a recent study, Myriam Valero, a population geneticist at Sorbonne University, Paris, and her colleagues, analyzed the genetics and mating of the red algae. After collecting seaweed samples and storing them in tanks, the team noticed hundreds of small, oblong crustaceans in the lab tanks. The discovery and the similarity of the spermatia of the algae and pollen led researchers to wonder if crustaceans played a role in the pollination of the algae, reports ScientificAmerican.

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Sex Cell Dispersal in Red Algae

Researchers placed male and female algae 15 centimeters apart with no water movement. Some tanks included Idotea balthica, an isopod crustacean, while others didn't. When successful fertilization occurs on the female algae, it creates bubble-like structures - cystocarp. By counting cystocarps, researchers quantified how many spermatia were reaching and fertilizing their female counterparts. When isopods were present in the tanks, fertilization was 20 times higher than in the control tanks.

Likewise, researchers set up tanks incubating only female algae and isopods exposed to male red algae earlier. Some of the females bore cystocarps, offering evidence that crustaceans - relatives of pill bugs - shuttle sex cells between the stalks of algae.

The team further confirmed the role of the isopods when looking at the crustaceans under a powerful microscope. Like bumblebees dusted with pollen, these marine animals had spermatia stuck all over their bodies.

The recent discovery hints that algae may have been among the first organism to reproduce using animals to spread its sex cells.

Conrad Labandeira, a paleontologist at the Smithsonian National Museum of Natural History, explains that the system could extend to the Precambrian era when red algae were present. Back in those days, the pollinators wouldn't have been the same isopods but rather early arthropod groups, reports ScienceNews.