Population collapse of habitat-forming species in the Mediterranean: a long-term study of gorgonian populations affected by recurrent marine heatwaves.

Daniel Gómez‐Gras ,J B Ledoux,R Amate,O Torrents,Àngel López‐Sanz ,Míkel Zabala ,Cristina Linares ,Nathaniel Bensoussan ,Silvija Kipson ,Ignasi Montero‐Serra ,Paula López‐Sendino ,Emma Cebrián ,Pierre Drap ,Frédéric Zuberer ,Maša Frleta‐Valić ,Christian Marschal ,Diego K Kersting ,Marta Pagès‐Escolà ,Núria Teixidó ,Alba Medrano ,Donna Dimarchopoulou ,Olivier Bianchimani ,Joaquim Garrabou

doi:10.1098/rspb.2021.2384

Abstract

Understanding the resilience of temperate reefs to climate change requires exploring the recovery capacity of their habitat-forming species from recurrent marine heatwaves (MHWs). Here, we show that, in a Mediterranean highly enforced marine protected area established more than 40 years ago, habitat-forming octocoral populations that were first affected by a severe MHW in 2003 have not recovered after 15 years. Contrarily, they have followed collapse trajectories that have brought them to the brink of local ecological extinction. Since 2003, impacted populations of the red gorgonian Paramuricea clavata (Risso, 1826) and the red coral Corallium rubrum (Linnaeus, 1758) have followed different trends in terms of size structure, but a similar progressive reduction in density and biomass. Concurrently, recurrent MHWs were observed in the area during the 2003–2018 study period, which may have hindered populations recovery. The studied octocorals play a unique habitat-forming role in the coralligenous assemblages (i.e. reefs endemic to the Mediterranean Sea home to approximately 10% of its species). Therefore, our results underpin the great risk that recurrent MHWs pose for the long-term integrity and functioning of these emblematic temperate reefs.

Highlights

The disturbance regimes of marine ecosystems are shifting worldwide due to anthropogenic climate change
Our results provide insights into the trajectories that marine heatwaves (MHWs)-impacted populations of Mediterranean octocorals could follow in the face of climate change
Predictions of shifts in the structure and functioning of temperate reefs under climate change are challenged by a poor understanding of the long-term recovery capacity from MHWs of their habitat-forming species

Summary

Introduction

The disturbance regimes of marine ecosystems are shifting worldwide due to anthropogenic climate change. In the Mediterranean, MHWs are frequently impacting the coralligenous assemblages, which are temperate reefs harbouring approximately 10% of Mediterranean species [3,7] Within these reefs, the habitat-forming octocorals (e.g. Paramuricea clavata and Corallium rubrum) have been among the most affected organisms, providing excellent biological models to explore the resistance and recovery capacity. To further explore the trajectories of the monitored populations over the monitored periods with respect to the ones that they should have followed if remaining undisturbed or having totally recovered, we represented their log–log biomass against density values in relation to their species-specific self-thinning lines [29].

Results

E Corallium rubrum n colonies m–2 n colonies m–2

Findings

Discussion