Thermal Performance of Seaweeds and Seagrasses Across a Regional Climate Gradient

Scott Bennett,Marina Forteza,Núria Marbà,Raquel Vaquer-Sunyer,Guillem Roca,Gabriel Jordá

doi:10.3389/fmars.2022.733315

Abstract

Comparative patterns in thermal performance between populations have fundamental implications for a species thermal sensitivity to warming and extreme events. Despite this, within-species variation in thermal performance is seldom measured. Here we compare thermal performance both within-species and between-species, for two species of seagrass (Posidonia oceanica and Cymodocea nodosa) and two species of seaweed (Padina pavonica and Cystoseira compressa) across the Mediterranean Sea. Experimental populations from four locations representing between 75 and 99% of each species thermal distribution and a 6°C gradient in summer temperatures, were exposed to 10 temperature treatments between 15 and 36°C. Experimental thermal performance displayed the greatest variability between species, with optimal temperatures differing by over 10°C within the same location. Within-species differences in thermal performance were also important for P. oceanica which displayed large thermal safety margins within cool and warm-edge populations and small safety margins within central populations. Our findings suggest patterns of thermal performance in Mediterranean seagrasses and seaweeds retain deep “pre-Mediterranean” evolutionary legacies, suggesting marked differences in sensitivity to warming within and between benthic marine communities.

Highlights

Ocean warming is altering the distribution and abundance of species across the globe (HoeghGuldberg and Bruno, 2010)
While many of these impacts have been concentrated in warm edge populations (Wernberg et al, 2016), cooler, central populations can be highly sensitive to extirpation (Marba and Duarte, 2010; Bennett et al, 2015), highlighting that not all species or locations are susceptible to warming
If individuals display similar thermal limits irrespective of range position, thermal safety margins will decrease toward the warm edge of a species range, creating a gradient of increasing thermal sensitivity from cool to warm edge populations (Bennett et al, 2019)

Summary

INTRODUCTION

Ocean warming is altering the distribution and abundance of species across the globe (HoeghGuldberg and Bruno, 2010). If individuals display similar thermal limits irrespective of range position, thermal safety margins will decrease toward the warm edge of a species range, creating a gradient of increasing thermal sensitivity from cool to warm edge populations (Bennett et al, 2019) This is a common assumption used in many species distribution models, for example, that rely on the realised distribution of species to predict the likelihood of extirpation or range shifts under climate change (Araújo and Peterson, 2012; but see Martínez et al, 2014; Valladares et al, 2014). The Mediterranean Sea settled to its current climatic conditions approximately 2000 years ago (Bianchi et al, 2012), characterised by a steep 6◦C climatic gradient from west to east Despite their evolutionary resilience, seaweeds and seagrasses are susceptible to contemporary warming in the Mediterranean. This work addresses underlying differences in thermal sensitivity predictions that arise from scaling issues in climate change ecology and contributes toward more nuanced, scalable links between geography and thermal physiology

MATERIALS AND METHODS

RESULTS

DISCUSSION

ETHICS STATEMENT