Estimating biodiversity changes in the Camargue wetlands: An expert knowledge approach

Abstract

Mediterranean wetlands are critical strongholds for biodiversity and the provision of ecosystem functions and services; yet, they are being severely degraded by a number of socio-economic drivers and pressures, including climate change. Moreover, we still lack comprehensive understanding of the extent to which biodiversity loss in Mediterranean wetlands will accelerate change in ecosystem processes. Here, we evaluate how changes in biodiversity can alter the ecosystem of the Camargue (southern France). We collected data on species presence/absence, trends and abundance over a 40-year period by combining observations from the scholarly literature with insights derived from expert knowledge. In total, we gathered more than 1500 estimates of presence/absence, over 1400 estimates of species abundance, and about 1400 estimates of species trends for eight taxonomic groups, i.e. amphibians, reptiles, breeding birds, fish, mammals, dragonflies (odonates), orthopterans and vascular plants. Furthermore, we used information on recently arrived species and invasive species to identify compositional changes across multiple taxa. Complementing targeted literature searches with expert knowledge allowed filling important gaps regarding the status and trends of biodiversity in the Camargue. Species trend data revealed sharp population declines in amphibians, odonates and orthopterans, while birds and plants experienced an average increase in abundance between the 1970s and the 2010s. The general increasing trends of novel and invasive species is suggested as an explanation for the changing abundance of birds and plants. While the observed declines in certain taxa reflect the relative failure of the protection measures established in the Camargue, the increasing exposure to novel and invasive species reveal major changes in the community structure of the different taxonomic groups. This study is the first attempt to assess changes in biodiversity in the Camargue using an expert knowledge approach, and can help manage the uncertainties and complexities associated with rapid social-ecological change in other Mediterranean wetlands.

The future for Mediterranean wetlands: 50 key issues and 50 important conservation research questions

“…Populations of many native, wetland-dependent species have been declining over the past half-century (MWO 2018;Fraixedas et al 2019). It seems likely that these trends will continue [I16] given the pressures highlighted in our horizon scan and their cumulative effect on habitat fragmentation [I17].…”

“…For example, the Mediterranean lost approximately 50% of its natural wetland surface area over the twentieth century (Perennou et al 2012) and a sample of natural wetland sites shrunk by 45-51% on average between 1970 and 2013 (MWO 2018). Wetland-dependent amphibians, reptiles, mammals, fish, odonates and orthopterans have all recently experienced large declines in abundance over recent decades (MWO 2018;Fraixedas et al 2019). Critically Endangered species include the Adriatic sturgeon Acipenser naccarii, the Greek red damselfly Pyrrhosoma elisabethae and the beautiful water-starwort Callitriche pulchra (IUCN 2020).…”

Community homeostasis of coastal microbial mats from the Camargue during winter (cold) and summer (hot) seasons

“…The Camargue, which is the delta of the Rhone River, has two distinct regions: the northern part, from the city of Arles to the Vaccares lagoon, is cultivated for rice, and the southern part, containing numerous lagoons of brackish water, is a site of salt harvesting, and where the microbial mats were sampled. Rice farming poses a risk for microbial mats due to the use of pesticides and fertilizers (Fraixedas et al, 2019; Osman et al, 2019) (Figure 1).…”

Field margins as substitute habitat for the conservation of birds in agricultural wetlands

“…Biodiversity associated with these rice paddy landscapes includes both waterbirds and terrestrial bird species. While the role of rice paddy landscapes for waterbirds has been largely studied, their role for terrestrial birds has received much lower attention (Elphick, 2015), whereas they have suffered a very significant decline since the 1950s due to the intensification of agricultural practices and the decrease of landscape heterogeneity (Fraixedas et al, 2019; Sirami et al, 2019). Terrestrial birds using rice paddy landscapes include different ecological guilds: reedbed birds, which are primarily associated with freshwater marshes (Morganti et al, 2019); forest edge species, which are originally associated with forest borders and clearings (Hinsley and Bellamy, 2019; Newton, 2017); and grassland species, which originally live in grassy or shrubby vegetation with no tree cover (Di Giacomo et al, 2010).…”

“…It is also the fifth European rice production area (FAO, 2018). If agriculture plays a critical role in the hydrosaline equilibrium of the delta by pumping freshwater from the Rhône River, farmland birds have shown the highest rate of decline in the last 50 years (Fraixedas et al, 2019; Galewski and Devictor, 2016). Hence, it is critical to better understand how field margins and semi-natural habitats remaining within agricultural landscapes may contribute to the restoration of biodiversity.…”