MacLIFE to study subantarctic islands rivers ecosystems

One of the areas of the world where climate change (CC) effects are the strongest is the Southern Ocean. It does affect ocean functioning, its biodiversity, it interacts with Antarctic ice dynamics, at various spatial and temporal scales. In the immensity of this ocean, patches of terrestrial life and remarkable associated biodiversity are spread thin: the belt of subantarctic islands. They harbour extraordinary avian, mammalian, plant life, part of it often endemic to one island. These islands however are also strongly sensitive to two anthropogenic factors: introduced non native species, and climate change.

Drying ponds and outlets in the subantarctic islands landscape under the effect of climate change. Picture from J. Labonne.

While the impacts of a number of terrestrial introduced non indigenous species (NIS) on native biodiversity and terrestrial ecosystems dynamics is now investigated, and partly documented, there is yet no information about the effect of non native freshwater species introductions on the functioning of river ecosystems. Likewise, next to nothing is known on the effect of CC on the rivers functioning. This gap in knowledge presents two problems: first, it underlines our lack of understanding of basic ecosystem functions in these latitudes – most of the available knowledge originates from European and American streams – and second, it prevents us to develop adapted mitigation strategies for environment and biodiversity managers.

The Kerguelen islands harbour a wide range of ecosystems, especially for freshwater ecosystems.

The MacLIFE initiative elected to tackle this challenge, and applied to the French Polar Institute to develop a research program in the subantarctic Kerguelen islands. These islands were introduced with 8 species of salmonids fish, the first natural reproduction observed in 1962. 5 species remain, and some of them, like brown trout, invade the whole archipelago.

Above view of the Marion Dufresne, the scientific ship operated by the TAAF and the French Polar Institute to support the scientific programs and wildlife conservation in the subantarctic territories.

We built a program in three steps. First, we will document the spread and structure of NIS of salmonids in the archipelago, based on our available long term data, samples collections, and by performing new survey of the current extent of their presence. This will allow us to estimate absence or presence of each species, their density and population structures.

Second, we will establish a baseline of the river ecosystems functioning in the archipelago. This will be done by sampling communities, establishing trophic networks, and measuring matter and energy flows. We will monitor water quality, biomass of biofilm and diversity of macro-invertebrates, and the relation to CO2 emission. We will take specific care to monitor rivers that have long been liberated by ice from those that are yet under the effect of the ice cap melting, and attempt at capturing the pace of ecological succession downstream the ice cap.

Typical landscape downstream the melting Cook ice cap in Kerguelen islands. Pictures from J. Labonne, INRAE.

Third, we will endeavour at finding the effects of NIS salmonids on the functioning of the rivers. This step will be tremendously bolstered by our available database on the distribution of salmonids, and the new update that will be obtained in the next expeditions. We will thus be able to contrast the dynamics of rivers with respect with presence, absence , diversity and quantity of NIS.

Some of the critters found in and around Kerguelen rivers, that enter the diet of resident salmonids. Some are endemic, like the caterpillar of Pringleophaga kerguelensis (upper left), some are introduced and invasive such as the merizodus (bottom right). Picture from S. Glise, INRAE.

Finally, we will also investigate the eco-evolutionary feedback between river ecosystems and communities, and the population structure of NIS on the colonization front. In particular, we will investigate the relationship between the river ecosystems and the evolution of life history traits and their underlying genetic drivers.

The MacLIFE community applied to get two expeditions, from 2023 to 2025, in order to develop this new research program, that will complete our activities in temperate regions of the northern hemisphere. We expect our program to be evaluated in December 2022, so fingers are kept crossed until then.