Aquatic communities of bromeliads

Most epiphytic bromeliads retain water at the base of their leaves, forming a suspended mini-aquatic ecosystem. The plant draws its nutrients from these reservoirs at the base of each leaf, using its roots only to anchor itself to the supporting tree.

In each of these small water tanks, dead leaves that have fallen from the high branches of the support tree accumulate and decompose under the action of micro-organisms and small detritivorous invertebrates. These decomposers convert the leaves to the ultimate stage of mineral salts, which are then available to the plant itself. We can therefore speak of a true mutualistic association between the plant that provides an aquatic habitat for this microfauna and the microfauna that provides it in return with a rare nutrient, mineral nitrogen, so prized by the plant.

While the aquatic communities of tank bromeliads in the understorey are relatively well studied, those in the canopy have never been the subject of in-depth studies. A fairly comprehensive study method was applied in the Life On Trees programme for each of these mini aquatic ecosystems in order to maximise the inventory of all the living organisms in these small pools perched in the highest parts of the tree.

The contents of dozens of bromeliads were taken from all three trees and brought back to the base camp. This water was then treated and filtered in the field to extract the various organisms.

Several hundred samples were packaged. Some will be analysed to identify all the small aquatic organisms (protists, rotifers, nematodes, etc.) using both microscopy and DNA analysis methods. Samples conditioned for invertebrates will be analysed by a specialist in aquatic invertebrates. The environmental DNA targeting vertebrates (amphibians, reptiles, mammals and birds) will be analysed from the organic matter sedimented in bromeliad pits. Initial environmental DNA results have been conclusive, with traces of DNA from birds, mammals and amphibians, most of which are difficult to detect using more conventional methods.

Thanks to all of these protocols, we hope to make the most complete inventory possible of all the eukaryotic biodiversity associated with the bromeliads in the study trees, from the smallest unicellular eukaryotes such as paramecia, to the largest mammals that regularly visit the canopies to feed.