On land, birds and bees are very effective pollinators; however, it is unclear how this essential process is carried out in marine environments. Small marine worms and crustaceans were shown to be responsible for transporting pollen from one blossoming seagrass plant to another by researchers ten years ago. Now, another study team has uncovered what may be a new pollinator. In this scenario, the organism in question is a slender crustacean known as an isopod. As it grazes on red algae, the isopod transfers its sperm cells from its body to the plant, therefore fertilizing it.
Myriam Valero, a population geneticist at the French national research agency CNRS, has spent a significant amount of time in the tidepools of Europe doing research on the genetics of the red alga Gracilaria gracilis. It’s rare for the plant to reproduce in this way. In many marine animals, the sperm and egg cells of men and females are released into the ocean to combine with those of other marine organisms. On the other hand, the situation is more difficult when it comes to Gracilaria: Egg cells are not released by the female alga, but rather kept inside funnel-shaped filaments until they are ready to hatch. Even though the cells do not have tails to assist them in swimming, the male’s sperm still has to find a way to reach them.
Valero observed that the algae were often covered by crawling isopods, which are crustaceans that are around 4 centimeters in length and resemble thin pillbugs. She pondered the possibility that a certain species of Idotea, Idotea balthica, was the one responsible for transferring sperm from male to female algae. It was evident, upon examination with a microscope, that minute sperm adhere to the isopod. She explains that they started to consider the possibility that it may perform the same function as a pollinator.
The long-held belief that animal-mediated pollination is absent in the sea has recently been contradicted in seagrasses, motivating investigations of other marine phyla. This is particularly relevant in red algae, in which female gametes are not liberated and male gametes are not flagellated. Using experiments with the isopod Idotea balthica and the red alga Gracilaria gracilis, we demonstrate that biotic interactions dramatically increase the fertilization success of the alga through animal transport of spermatia on their body.
The group of researchers began by cultivating virgin female algae in the laboratory before introducing them to tanks containing male algae. Isopods were introduced into some of the aquarium tanks. The team published its findings today in the journal Science. They found that the algae that lived with the crustaceans were around 20 times more effective at reproducing. This was determined by the number of fertilized structures known as cystocarps.
Valero has the impression that the connection is advantageous for both parties in a number of ways. Because Idotea is often the same color as the plant, it is possible that the alga is providing a spot for younger isopods to hide from predators. The crustaceans also feed on diatoms, which are single-celled algae that develop on the red algae and are consumed by the crustaceans as food. Isopods may get their nourishment from this particular source. According to the findings of other studies, keeping the red algae clean encourages their rapid growth.
Nevertheless, this symbiosis seems to be far less complex than the highly specialized partnerships that exist between insect pollinators and plants that grow on land. In these associations, flowers and insects have coevolved morphology and behavior that optimizes pollination. Why is anything like this so uncommon in the ocean? Rick Grosberg, a marine evolutionary scientist at the University of California, Davis, pointed out that it may be related to the physics of living in water, which is considerably denser than air. He says this might be the case since water is much more dense than air. It’s possible that the energy gained from the nectar isn’t worth the work it takes to swim near the bloom in the first place.
It has not yet been determined whether or not isopods are successful at pollinating algae in their natural environments; other experts point out that the current study only reveals that isopods can pollinate algae in lab aquaria. Additionally, Don Levitan, a marine biologist at Florida State University, speculates that wind and waves may be more successful in dispersing the sperm of the algae than other environmental factors.
Ecological interactions may take many forms, but they all play a role in driving biodiversity and keeping it alive. However, even the most basic interactions between isopods and algae might be put in jeopardy by climate change or the acidity of the water, as Valero points out; this could wind up being detrimental to one or both of the species. To have a comprehensive awareness of the risk, it is necessary to acquire a deeper comprehension of the types of interactions involved.