It always counts as a surprise when we find out that unexpected networks have been operating right under our collective noses. We use the word ‘discovery’ to describe the newness to our understanding, even if, in retrospect, it might be a bit like describing a city’s take-out food delivery system as a ‘discovery’ just because no one had noticed a connection between all the scooters with restaurant names and the arrival of restaurant food at private homes.
The discovery, in this case, is something that makes a lot of sense: At least one kind of sea grass that flowers underwater manages to employ underwater pollinators in a manner similar to terrestrial flowering plants that use airborne pollinators like bees, bats and birds.
There aren’t many plants that actually flower under water – most produce their flowers above the water surface. Thalassia testudinum, known as turtlegrass, grows in large meadows, and produces small flowers near the seabed. The male flowers release pollen in the evening, and until now it was thought that the pollen was carried to female plants solely via water currents.
But a study published last fall in Nature Communications showed that there is another factor that increased the distribution of pollen. In a series of aquarium-based experiments, it was demonstrated that a variety of invertebrates, from spider crab larvae to tiny crustaceans to marine worms, are drawn to the male and female flowers, and these fauna were proven to fulfil the criteria of being characterized as pollinators* even in the absence of water flow.
The researchers from the National Autonomous University of Mexico state that that other, larger animals might also contribute to pollination, but that these were not included in this particular study. Unlike bees, there’s no hive or honey involved. But, like their terrestrial counterparts, the fauna here were attracted to the flowers for feeding, and moved between the blossoms in search of more food.
A male turtlegrass flower releases its nocturnal pollen. Photo: ICMyL via DGCS
Look at the intelligence of turtlegrass. It has small flowers, and they aren’t packed densely together, waving in the breeze. Rather, they are close to the sea bed and spaced well apart. Relying solely on water flow to pollinate might not do the trick. Why not make the petals sticky and attractive to the myriad small creatures abundant in the water, and get them to do a bit of the heavy pollen lifting for extra evolutionary insurance?
I applaud lead researcher Brigitta van Tussenbroek and her research team for noticing and studying this fascinating network of activity, which they have given the name zoobenthophilous pollination, i.e. pollination carried out by animals close to the sea bed. The discovery of the role fauna play in underwater pollination could help better understand and protect these ecosystems, which, as van Tussenbroek and her colleagues state, “are amongst the world’s most productive ecosystems. (They) improve water transparency, stabilize coastlines and store carbon, and also provide food and shelter to a diverse faunal community.”
I have the feeling it may just be the beginning of a deeper understanding of many things that are right in front of us, but which we aren’t yet seeing. All it requires is a willingness to shift our perspective.
A female turtlegrass flower with visiting invertebrates, bits of pollen and sand. Photo: ICMyL via DGCS
*From the study “Experimental evidence of pollination in marine flowers by invertebrate fauna” the criteria for the animals to be considered pollinators are:
(1) both male and female organs (of the flowers) are visited, (2) the visitor carries pollen, (3) the visitor transfers pollen between male and female sexual organs, (4) pollen deposition by the visitor results in successful fertilization, estimated as pollen germination on the stigmas, pollen tube growth or seed set.