Six freshwater plants depend on the sea on Kerguelen | Polarjournal
Between moss-covered peat bogs and glacial valley lakes, water-logged troughs mostly line the gentle slopes of the sub-Antarctic island coasts. A few rare flowering plants find refuge there, plants that are fond of spaces rich in nutrients brought by marine animals. Image: Camille Lin / TAAF

At the convergence of the Southern, Pacific, Atlantic and Indian Oceans, the sub-Antarctic islands are home to some rare freshwater aquatic plants. They live in pits filled with water where southern elephant seals take baths as well as in temporary pools. Anne-Kristel Bittebiere, a biologist from the University of Lyon, is interested in the ecology of the 6 native species that thrive naturally on the Kerguelen archipelago. “It is not so much the rain, nor the heat that structures the distribution of Ranunculus, the small short rush, the Southern limosella or the Antarctic callitrich, but their proximity to the ocean as animal activity coming from the open ocean brings nutrients.”

The researcher and her colleagues from Lyon, Rennes and Paris published their first results on the subject in Polar Biology in early April. These results are of interest to the managers of the French Southern Territories National Nature Reserve: “Scientific knowledge of these species is essential to protect them, both in terms of their biology and their ecology,” says Clément Quétel, head of the Conservation and Restoration of Natural Environments Department.

When she went to the site with the French Polar Institute in 2016, the biologist realized that aquatic plants were sheltering in these water-filled holes used by animals to bathe. “We went to the Molloy side [ancienne base géophysique], followed the rivers and looked for where freshwater aquatic plants could find habitats to grow.” she continues.

The Kerguelen archipelago is dotted with freshwater aquatic ecosystems, such as temporary pools, ponds, lakes, peat bogs, seeps between rocks, hot springs, but also southern elephant seal troughs.

At present, the origin of the formation of the southern elephant seal troughs is not known. Do these marine mammals create a pit through their movements over time? Or do they simply use these depressions dug by natural erosion to rest? One thing is clear, their presence enriches the environment with nutrients that are beneficial to plants, either when they moult or complete their digestive cycle. Image: Camille Lin / TAAF

“On the Courbet Peninsula, the ponds temporarily get drier, which is normal in the summer. But this year 2022-2023 it was very dry and they dried out more than usual.” she explains. “Normally, the levels don’t have much effect on these aquatic plants, even if the water has temporarily receded from the pond, they can survive.” On the other hand, temperature variations accentuated by global warming can affect their metabolism.

“Limosella that we keep in culture at the laboratory in Lyon multiplies by cloning,” she adds. On the island, ranunculus and other aquatic plants could be dispersed by Eaton’s pintails, which are common in these wetlands, by scattering seeds or plant pieces.

“In rivers, there may be algae, but no flowering plants and very little vegetation. There are not many vital nutrients like nitrate or phosphorus and long the edge, only mosses grow. But annual floods could wash them away. The farther you get from the coast, the fewer pools there are and the fewer nutrients there are, too,” notes the biologist.

These specific plants have very limited distribution areas and we find some species on Marion Island or on other subantarctic islands. Limosella is also present in the northern hemisphere, as on Saint-Pierre-et-Miquelon, off the coast of Canada. Only the buttercup Ranunculus moseleyi would be endemic to the archipelago.

Camille Lin, PolarJournal

Taxonomic details: As specified by Pierre Agnola, in charge of the conservation programs of the flora and habitats of the National Nature Reserve of the French Southern Territories, the 6 species of flowering plants that are part of the freshwater aquatic ecosystems of the Kerguelen archipelago are three species of ranunculus: 1. Ranunculus biternatus ; 2. Ranunculus pseudotrullifolius ; 3. Ranunculus moseleyi. As well as short rush (Juncus scheuchzerioides), Southern limosella (Limosella australis) and Antarctic callitiche (Callitriche antarctica).

Link to study: Douce, P. et al(2023). Biotic and abiotic drivers of aquatic plant communities in shallow pools and wallows on the sub-Antarctic Iles Kerguelen. Polar Biol. https://doi.org/10.1007/s00300-023-03122-y.

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