Banc d'Arguin National Park

Abstract Throughout its range, the Eurasian spoonbill Platalea leucorodia is migratory, but there is a well-documented exception in a population living in the Parc National du Banc d’Arguin in Mauritania. Based on their smaller body size, absence of a yellowish breast band during breeding, and fully black bills, they were assigned subspecies status ( Platalea leucorodia balsaci ) in 1974. Despite obvious threats (small numbers, and their low-lying breeding islets being under pressure from sea level rise), the Mauritanian spoonbill has not been assessed for inclusion on the IUCN Red List. The nominate subspecies P. leucorodia leucorodia , which joins the Mauritanian subspecies at Banc d’Arguin during the non-breeding season, is categorized as Least Concern. There is genetic and behavioural evidence of gene flow between balsaci and leucorodia , and in December 2023 and 2024, we observed that over half of the spoonbills born at Banc d’Arguin (identifiable by their colour-rings) had the yellow-tipped bill characteristic of leucorodia . As the increase in the marked balsaci population has not resulted in resightings away from Banc d’Arguin in the well-monitored flyway of leucorodia from West Africa to Europe, the introgression of leucorodia genes into balsaci seems to have left the isolating character of residency of the Banc d’Arguin-breeding spoonbills intact. We propose that the subspecies balsaci should be categorized as Vulnerable on the IUCN Red List. We recommend continued monitoring of the breeding population of balsaci , with the inclusion of new studies of morphology and genetics.

The Banc d’Arguin is the most ecologically significant coastal wetland of West Africa, a UNESCO Marine World Heritage area with one of the most extensive seagrass areas on Earth, used by many marine species as breeding and/or feeding habitat. However, little is known about the subtidal biodiversity supported by these extensive seagrass meadows. This study aimed to assess the influence of subtidal seagrass vegetation on fish assemblages, using beach seines to compare vegetated and unvegetated habitat. Effects of season and site were also assessed. We sampled fish communities predominantly composed of juveniles (98.7%). Specifically, we analyzed differences in abundance, species richness, diversity, evenness, and assemblage structure across these factors. Season was the most influential driver of fish assemblage structure, even more than habitat, as expected in a nursery area where fish reproduce seasonally. Notably, four species - Atherina boyeri , Eucinostomus melanopterus , Mugil capurrii , and Chelon dumerili - accounted for 53.7% and 49.2% of the variation in assemblages across habitat and season, respectively. Moreover, four times as many species were found exclusively in seagrass habitats compared to unvegetated areas, underscoring the critical role of seagrass meadows in the Banc d'Arguin in supporting species that depend on such shallow sheltered habitats, enhancing regional biodiversity, and contributing to the sustainability of fisheries. • Seagrass habitats buffer variability of fish assemblages • Four times more exclusive species in vegetated than unvegetated areas • Seasonal recruitment drives fish assemblage structure more than habitat type • Juveniles dominate fish assemblages, with four species explaining 45% of variation • Multivariate analyses reveal hidden patterns in complex ecological systems

Studying the breeding patterns and diet of conspicuous predators is a useful way to understand the structure of marine coastal food webs. The Banc d'Arguin, Mauritania, hosts a significant portion of the West African population of a widespread and conspicuous fish predator, the Caspian Tern Hydroprogne caspia. At two small islands, the relatively offshore Arel and the inshore Zira, in the Parc National du Banc d'Arguin, the size of the colonies and the timing of the first wave of breeding were measured during the breeding seasons 2015–2018. At Arel, the summed number of nests counted varied between 128 in 2015 to 306 in 2018 and at Zira between 375 in 2015 to 279 in 2018. Breeding at Arel commenced about a month later than at Zira. During the breeding season of 2016, the diet of Caspian Terns was assessed by the identification of hard items found in pellets collected near nests. All of these appeared to be parts of fish (e.g., otoliths, bones, vertebrae, scales, bullae and atlas). Despite the effort, for Arel 47% and for Zira 45% of the fish parts remained unidentified. Nevertheless, diet composition differed in interesting ways between the two colonies. At offshore Arel, the identifiable part of the diet consisted primarily of pelagic species, namely Hemiramphidae, while at inshore Zira, pellets consisted primarily of bentho-pelagic prey, namely Cichlids. Repeated sampling across years may show whether the evidence for earlier inshore breeding holds up and is consistently correlated with dietary differences.

Coastal systems store enormous carbon quantities in their sediment, which originates from various autochthonous and allochthonous sources. Carbon fluxes in coastal ecosystems have a strong effect on the recipient food-webs and carbon emission offsets. Yet, the relative importance of autochthonous vs. allochthonous C inputs to coastal carbon budget is still challenging to identify. Here, we combine diatoms preserved in the sediment with geochemical analyses to identify the sources of carbon stored in Africa’s largest intertidal seagrass beds at Banc d’Arguin, Mauritania. The area lies between an active ocean upwelling and the ‘Sahara-dust hotspot’ systems. The extensive seagrass beds of the area are thus expected to receive C from these neighboring systems in addition to producing C in-situ. Three sediment cores (50 cm) were collected at three intertidal sites with different hydrodynamic regimes, and analyzed for diatom composition, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and carbon isotopic signatures (δ13C). Diatom taxa are grouped into three guilds: (1) benthic (epiphyte, epipelon, and epipsammon), (2) planktonic, and (3) freshwater. Benthic diatoms are considered to be autochthonous, while typical oceanic and freshwater diatoms are considered to be allochthonous. Benthic diatoms are the most diverse and abundant group, while allochthonous freshwater (i.e., dust imported) and typical upwelling (i.e., tidal imported) taxa ranked last in both abundance and species’ richness. Structure equation modelling shows that variation in the stored carbon is best explained by the total abundance of diatoms and guild composition. We conclude that the C stored in the intertidal seagrass beds of Banc d’Arguin is predominantly autochthonous. Our method provides an effective way to identify historical carbon sources in coastal systems.

Abstract Marine coastal ecosystems are crucial to human populations in reducing disaster risk. Least Developed Countries are particularly vulnerable to the effects of climate change, such as sea‐level rise and storm surges. The Mauritanian coast, West Africa, ranks among the most vulnerable worldwide to sea‐level rise, and coastal communities in the National Park of Banc d’Arguin (PNBA) are particularly at risk. Here, we assessed the service of coastal protection in PNBA by (1) mapping the coastal marine ecosystems with Sentinel‐2 imagery and determining their spatial wave height attenuation rates; (2) assessing the vulnerability of villages and natural habitats to coastal hazard risk; and (3) assessing the applicability of coastal protection measures in the PNBA. We found that a total of 83% of the populated coastline presents a moderate to high risk of flooding and erosion, with Iwik and R’Gueiba being the most threatened villages in the PNBA. As for the ecological risk, two low‐elevated islands, which support breeding colonies of birds, are particularly vulnerable to sea‐level rise. However, in other areas, the rupture in the dune cord created new lagoons that present valuable ecological and economic interests like the Lagoon of Bellaat. Improving the comprehension of wave attenuation provided by coastal habitats, combined with identifying the vulnerability and applicability of coastal protection measures, is essential for achieving the Sendai Framework for Disaster Risk Reduction goals. In the PNBA, relocation of identified villages at risk is probably the best cost‐effective solution with the least disturbance to both breeding and wintering birds. Protection of coastal ecosystems will also ensure a continued provision of other ecosystem services, including food supply for sea dependent populations, and contribute to achieving the Paris Agreement and Sustainable Development Goals.

In 1974 R. de Naurois and F. Roux proposed that the distinct morphology of Eurasian Spoonbills Platalea leucorodia breeding on offshore islands in the Banc d'Arguin, Mauritania, in comparison with the sympatrically wintering northwest European breeding Spoonbills Platalea leucorodia leucorodia, justifies recognition as a separate subspecies Platalea leucorodia balsaci. This proposal is examined here on the basis of variation in nuclear DNA, microsatellites identified earlier for P. minor and P ajaja. We show that there is significant variation between Spoonbills breeding in Mauritania (n = 25) and the sympatrically wintering conspecifics breeding in the Dutch Wadden Sea (n = 105). Of the total genetic variation among the 130 individuals, 6.3% is attributable to variation between the two breeding areas (93.7% of the variation is within breeding areas). Pairwise FST values showed low genetic differentiation (FST'S < 0.012) among breeding colonies within The Netherlands. The level of genetic differentiation indicates that the level of gene flow between The Netherlands and Mauritania is much lower (∼4–5 individuals/generation) than among the Dutch colonies on separate Wadden Sea islands. Field observations on individually colour-marked birds from The Netherlands indeed suggest extensive dispersal within northwest Europe, with some introgression of leucorodia genes into the balsaci population. The level of microsatellite distinctiveness between sympatric populations of the two subspecies is similar to that recorded for subspecies of other migrant birds, and as such justifies the subspecies status of the Mauritanian Spoonbill.

IUCN, WWF and the US National Oceanic and Atmospheric Administration (NOAA) have developed this guidebook to assist marine protected area (MPA) managers in assessing the performance of their MPA. Based on this assessment, it shows how necessary changes can be made to improve management measures. It presents a flexible approach that can be used in many types of MPA and offers a variety of specific biological, socio-economic and governance indicators to measure the effectiveness of management actions in achieving MPA goals and objectives.