Marine Heat Waves Hazard 3D Maps and the Risk for Low Motility Organisms in a Warming Mediterranean Sea

Giovanni Galli,Cosimo Solidoro,Tomas Lovato

doi:10.3389/fmars.2017.00136

Abstract

Frequency and severity of heat waves is expected to increase as a consequence of climate change with important impacts on human and ecosystems health. However, while many studies explored the projected occurrence of hot extremes on terrestrial systems, few studies dealt with marine systems, so that both the expected change in marine heat waves occurrence and the effects on marine organisms and ecosystems remain less understood and surprisingly poorly quantified. Here we: i) assess how much more frequent, severe, and depth-penetrating marine heat waves will be in the Mediterranean area in the next decades by post-processing the output of an ocean general circulation model; and ii) show that heat waves increase will impact on many species that live in shallow waters and have reduced motility, and related economic activities. This information is made available also as a dataset of temperature threshold exceedance indexes that can be used in combination with biological information to produce risk assessment maps for target species or biomes across the whole Mediterranean Sea. As case studies we compared projected heat waves occurrence with thermotolerance thresholds of low motility organisms. Results suggest a deepening of the survival horizon for red coral (Corallium rubrum, a commercially exploited benthic species already subjected to heat-related mass mortality events) and coralligenous reefs as well as a reduction of suitable farming sites for the mussel Mythilus galloprovincialis. In recent years Mediterranean circalittoral ecosystems (coralligenous) have been severely and repeatedly impacted by marine heat waves. Our results support that equally deleterious events are expected in the near future also for other ecologically important habitats (e.g. seagrass meadows) and aquaculture activities (bivalvae), and point at the need for mitigation strategies.

Highlights

Climate change is expected to alter the average values of environmental properties, and the extreme ones, as well as the frequency of occurrence of conditions nowadays considered as extreme (Seneviratne et al, 2014)
As case studies we present maps of threshold exceedance for temperature and duration exposure values indicated as lethal for the mussel Mythilus galloprovincialis, the seagrass P. oceanica, and for the red coral Corallium rubrum, a key species of Mediterranean coralligenous habitats (Ballesteros, 2006)
Marine heat waves (MHWs) frequency data are more scattered with rather high values of standard deviation that are close to the mean differences (Figures S3.1B,E)

Summary

Introduction

Climate change is expected to alter the average values of environmental properties, and the extreme ones, as well as the frequency of occurrence of conditions nowadays considered as extreme (Seneviratne et al, 2014). While phenotypic plasticity can provide means for individuals to acclimate to adverse conditions, this is possible only within certain limits and, in any case, it comes at an energetic cost and leaves an organism stressed and more vulnerable to other pressures (Haguenauer et al, 2013). Both acclimation and adaptation mechanisms are likely to counterbalance slow gradual changes, but may be less effective in buffering the impact of extreme or episodic events. On land, an intensification of hot extremes throughout the Mediterranean area (Déqué et al, 2007; Diffenbaugh et al, 2007) whereas no such analysis is currently available for the Mediterranean marine environment, except for limited regions and/or depths (e.g., Jordà et al, 2012; Marbà et al, 2015)

Objectives

Methods

Results