It has long been known that animals help plants to reproduce on earth, it is pollination. We have just found the same thing underwater for the first time: a small crustacean that carries the gametes of a red algae.
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Nature has been quite unfair in organizing the reproduction of species. Some male gametes are equipped with what is called a flagellum (this is the case with the human spermatozoon): for them, it is quite simple to fertilize the female gametes. But others are not “conveyed” and must therefore find an ally, like this marvelous little crustacean, the idotée. It looks a bit like a 1 cm long shrimp which has the elegance to walk on this red algae, the gracillaria, to load its legs and its shell with slightly sticky male gametes and to go deposit in females. Exactly like a bee or a wasp goes from flower to flower to distribute pollen.
This is the very first time that this type of animal pollination has been demonstrated for algae. About fifteen years ago, we observed it with flowering marine plants, but algae is not a flowering plant, it’s more complicated (it has no root and organs of invisible reproductions.)
For 20 years that they have been working there, researchers from the National Center for Scientific Research (CNRS) in Roscoff, led by Myriam Valéro and Christophe Destombes, first thought that the current carried gametes. But in the rock basins where this red algae lives, they saw that it was more fertilized at low tide in calm water than at high tide with current. One day they noticed all these idotas clinging to the seaweed. They put them in two aquariums: male and female algae at 15 cm from each other, without idotées in the first, with in the second. Guess where there was the most fertilization? In the second of course. 20 times more.
The crustacean finds its account there too. The proof and it’s incredible: the crustacean does not eat the red algae (while it eats the others). It even washes away the humus that clutters it, which facilitates photosynthesis. And in return, we think that the algae shelters it and protects it from predators. We discover in any case with this publication of the review Science that pollination is much older than we thought (since these red algae are more than 800 million years old). We were talking about 140 million years for flowering plants.
We understand how precious this mutual aid between animals and plants is for biodiversity. And therefore to be protected. “It’s our food chain, it’s the balance of the oceans” remember Myriam Valero the researcher from Roscoff, expressing the wish that we think twice before concreting the ribs.