Warming Threatens to Propel the Expansion of the Exotic Seagrass Halophila stipulacea

Marlene Wesselmann,Carlos M Duarte,Ester A Serrao,Núria Marbà,Rosa M Chefaoui

doi:10.3389/fmars.2021.759676

Abstract

The spread of exotic species to new areas can be magnified when favored by future climatic conditions. Forecasting future ranges using species distribution models (SDMs) could be improved by considering physiological thresholds, because models solely based on occurrence data cannot account for plasticity due to acclimation of individuals to local conditions over their life-time or to adaptation due to selection within local populations. This is particularly relevant for the exotic seagrassHalophila stipulacea, which colonized the Mediterranean Sea a century ago and shifted its thermal niche, coping with a colder regime. Here, we used two hybrid models combining correlative SDMs with the thermal limits for growth of native and exoticH. stipulaceapopulations to predict the distribution of the species in its native (Indian Ocean and Red Sea) and exotic ranges (Mediterranean Sea and Caribbean Sea) under two scenarios forecasting limited (RCP 2.6) and severe (RCP 8.5) future climate changes by 2050 and 2100. Then, we assessed the differences between hybrid models based on native Red Sea thermal limits (niche conservatism: 17–36°C) and on exotic Mediterranean thermal limits (local adaptation: 14–36°C). At the Mediterranean exotic range, the local adaptation hybrid model accurately agreed with the present distribution of the species while the niche conservatism-based hybrid model failed to predict 87% of the current occurrences of the species. By contrast, both hybrid models predicted similar species distributions for the native range and exotic Caribbean range at present and projected thatH. stipulaceawill maintain its current worldwide under all future greenhouse gas emission scenarios. The hybrid model based on Mediterranean thermal limits projected the expansion ofH. stipulaceathrough the western Mediterranean basin (except the gulf of Leon) under the most severe scenario (RCP 8.5) by 2100, increasing its distribution by 50% in the Mediterranean. The future expansion ofH. stipulaceais related to its capacity to cope with warm waters and it may become a relevant species in the future, particularly under the projected decline of native Mediterranean seagrasses, resulting in important shifts in seagrass communities and overall ecosystem functions.

Highlights

Temperature regimes, a determinant factor controlling the biogeographic distribution of species (Brown et al, 2004; Dell et al, 2011), are expected to continue to increase due to the rise in anthropogenic emissions of greenhouse gases (Intergovernmental Panel on Climate Change [IPCC], 2014), driving a global redistribution of species with economic and ecological consequences (Pecl et al, 2017)
Habitat increases were projected for the south of the Red Sea, Seychelles, western Mediterranean and Atlantic coast of Morocco by 2050 and 2100 (RCP 2.6)
We show that the global future spread of Halophila stipulacea in contrasting climate change scenarios is better predicted when accounting for local adaptation as compared to niche conservatism

Summary

Introduction

Temperature regimes, a determinant factor controlling the biogeographic distribution of species (Brown et al, 2004; Dell et al, 2011), are expected to continue to increase due to the rise in anthropogenic emissions of greenhouse gases (Intergovernmental Panel on Climate Change [IPCC], 2014), driving a global redistribution of species with economic and ecological consequences (Pecl et al, 2017). Similar climatic conditions between native and recipient locations are key for successful biological invasion and establishment (Duncan et al, 2003; Thuiller et al, 2005; Bennett et al, 2021) and, it is expected that warming might accelerate the spread of exotic tropical species into warm temperate areas and/or increase their abundance, exacerbating their impacts (Bates et al, 2013; Poloczanska et al, 2013; Sorte et al, 2013; Bennett et al, 2021). In marine systems the impact of exotic species on recipient ecosystems is maximized where the median temperature is slightly (2.2◦C) cooler than the optimal average temperature at the original range of the species (Bennett et al, 2021)

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Discussion

Conclusion