Phenotypic Plasticity in Sargassum Forests May Not Counteract Projected Biomass Losses Along a Broad Latitudinal Gradient

Lidiane P Gouvêa,Eduardo Bastos,Giulia Burle,Cintia D L Martins,Gabrielle Koerich,Leticia M C Peres,Fernanda Ramlov,Eliza Fragkopoulou,Carlos F D Gurgel,Ester A Serrão,Jorge Assis,Paulo A Horta

doi:10.1007/s10021-022-00738-9

Lidiane P Gouvêa, Eduardo Bastos + Show 10 more

Open Access

https://doi.org/10.1007/s10021-022-00738-9

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Abstract

Phenotypic plasticity and local adaptation can adjust individual responses to environmental changes across species’ ranges. Studies addressing the implications of such traits have been underrepresented in the marine environment. Sargassum cymosum represents an ideal model to test phenotypic plasticity, as populations along the southwestern Atlantic Ocean display a sharp decrease in abundance toward distributional range limits. We (1) characterized the macroecological environment of S. cymosum across a latitudinal gradient, (2) evaluated potential differences in ecophysiological adjustments (biomass, photosynthetic pigments, phenolic compounds, total soluble sugars and proteins, and carbon–nitrogen—CN—content), and (3) tested for differences in thermal tolerance based on time series analyses produced from the present to contrasting representative concentration pathways scenarios (RCP) of future climate changes. Our results showed distinct macroecological environments, corresponding to tropical and warm temperate conditions, driving biomass and ecophysiological adjustments of S. cymosum. Populations from the two environments displayed contrasting thermal tolerances, with tropical individuals better coping with thermal stress when compared to more temperate ones (lethal temperatures of 33 °C vs. 30 °C); yet both populations lose biomass in response to increasing thermal stress while increasing secondary metabolites (for example, carotenoids and phenolic compounds) and decrease chlorophyll’s content, Fv/Fm, total soluble sugars concentration and CN ratio, owing to oxidative stress. Despite evidence for phenotypic plasticity, significant future losses might occur in both tropical and warm temperate populations, particularly under the no mitigation RCP scenario, also known as the business as usual (that is, 8.5). In this context, broad compliance with the Paris Agreement might counteract projected impacts of climate change, safeguarding Sargassum forests in the years to come.

Highlights

Higher population abundance is predicted in the center of species’ geographic distributions due to the prevalence of more favorable conditions, while from the center toward the edge, abundance is expected to decrease as conditions become less suitable (Brown 1984; Brussard 1984)
The cluster analysis using macroecological environmental variables divided the populations along the latitudinal gradient in two main clusters: tropical, comprising PI, PB, RN, BA, ES and warm temperate represented by SP, RJ and SC
Biomass, carbon and nitrogen (CN), and total soluble sugars presented higher concentrations in the tropics, while carotenoids, proteins and chlorophylls were higher in the warm temperate region (Figure 2b and Table S5)

Summary

Introduction

Higher population abundance is predicted in the center of species’ geographic distributions due to the prevalence of more favorable conditions, while from the center toward the edge, abundance is expected to decrease as conditions become less suitable (Brown 1984; Brussard 1984). When exposed to extreme thermal conditions, photosynthesis, resource utilization, and growth, as well as changes in carbon (C), nitrogen (N), proteins, and storage of carbohydrate content are straightforward indicators of cell’s physiological status (Torres and others 1991; Wernberg and others 2016; Gouvea and others 2017; Costa and others 2019). These indicators can be used to test for phenotypic plasticity between populations of contrasting ranges under increasing thermal stress

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