Predicted regime shift in the seagrass ecosystem of the Gulf of Arguin driven by climate change

Rosa M Chefaoui,Carlos M Duarte,M Abdoull Ba,M.A Sidi Cheikh,Ester A Serrao,Ana I Tavares,Duarte G Frade

doi:10.1016/j.gecco.2021.e01890

Abstract

The Banc d′Arguin is a marine ecosystem of global conservation significance, the largest bird sanctuary of western Africa, supported by one of the most extensive seagrass beds in the world composed by three seagrass species, two temperate near their southern limit ( Zostera noltei and Cymodocea nodosa ) and one tropical at its northern limit (Halodule wrightii) . Here we predict the fate of this seagrass ecosystem under climate change scenarios during the 21st century, using species distribution models and sea level rise estimates. We forecast a probable decline in total seagrass area of 3340 Km 2 (78%) by 2100, involving the loss of both temperate seagrasses ( Z. noltei, C. nodosa ), the foundational ecosystem components. By 2050, only the tropical species (H. wrightii) would remain , which forms thin and sparse shallow stands functionally distinct from the previous tall dense meadows that span wider vertical ranges. Intertidal flats, the essential bird foraging habitats, would become unvegetated and also suffer a major reduction in area (114 km 2 by 2050, 587 km 2 by 2100). The large projected loss of foundational seagrass species portends a collapse of major ecosystem functions with profound impacts on biodiversity, fishery resources and ecosystem services.

Highlights

The Gulf of Arguin on the western coast of Africa (Mauritania), facing one of the richest upwelling fishing regions, contains one of the most extensive pristine seagrass habitats on Earth (Tregarot et al, 2021)
A regime shift in the seagrass ecosystem of the Gulf of Arguin is expected considering the effects of climate change and sea level rise (SLR)
Our projections foretell a major loss of ecosystem structuring vegetation, so that the previous tall and broad-leaved C. nodosa canopies in the subtidal zone will retain only the shorter and thin tropical H. wrightii

Summary

Introduction

The Gulf of Arguin on the western coast of Africa (Mauritania), facing one of the richest upwelling fishing regions, contains one of the most extensive pristine seagrass habitats on Earth (Tregarot et al, 2021) These provide major feeding and/or breeding sites for a wide range of marine species, including seabirds, turtles, endangered elasmobranchs and species of commercial interest (Araujo and Campredon, 2016). Important coastal wetland in Western Africa, recognized for its unique universal value by the UNESCO’s Marine World Heritage Programme It is a globally significant hotspot for blue carbon, as it ranks as the third largest area of seagrass and the third largest carbon stock, as well as the fifth most extensive tidal marshes and carbon stocks among these UNESCO sites (Duarte et al, 2021). The PNBA is recognized as the most important habitat of the Western Atlantic for nesting birds and Palaearctic migratory waders (https://whc.unesco.org/en/list/506/)

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