Impact of climate change and ENSO on aerobic habitat in the South East Pacific

– Alexandra Parouffe, LEGOS –

Résumé :

On-going climate change (CC) has emerged as an additional anthropogenic threat to marine ecosystems across the world’s ocean. The oceans are warming at unprecedented rates and a global deoxygenation is materializing. The consequences on marine ecosystems are already observed.

The South East Pacific (SEP) hosts the Humboldt Current System (HCS), the most productive system in the world. It is associated with an Eastern Boundary Upwelling System (EBUS), an Oxygen Minimum Zone (OMZ), and is crossed by several seamount systems, hosting unique ecosystems composed of endemic species. Whereas the impact of climate change in the SEP physical processes has been well documented, the impact on marine organisms has been studied only weakly.

The response of organisms to CC is usually attributed to species thermal tolerance levels, which would be reached or exceeded with rising temperature. Temperature is a controlling driver of species physiology and metabolism. Rising temperature and changes in oxygen content modulate the oxygen supply and demand of aerobic organisms. In addition, if climate change impacts the SEP, it is also subjected to the largest climatic mode, the El Niño Southern Oscillation (ENSO), for which the effect on the SEP ecosystems are consequential but not well explained.

Therefore, the purpose of this study is to assess the pressure exerted by CC and ENSO on marine organisms in the future climate. We use metabolic constraints to infer the impact on organisms’ physiology. We hypothesise that changing oxygen and temperature due to CC or ENSO may cause mismatch between oxygen supply and demand, hence modulating habitat suitability.

We show that there are strong regional patterns of changes in habitat suitability. We find that whereas hypoxia tolerant species evolving in the vicinity of the OMZ may find improving conditions, most of the SEP organisms will face pressure from deoxygenation trends and warming, either due to ENSO or CC.

Jury :

• Andreas Oschlies, referee, GEOMAR, Germany
• Brad Seibel, referee , University of South Florida, USA
• Ana Queiros, examiner, Plymouth Marine Laboratory, UK
• David Veliz, examiner, Universidad de Santiago, Chile
• Boris Dewitte, examiner, CEAZA, Chile, and CECI, Toulouse
• Véronique Garçon, thesis co-director, IPGP, Paris
• Aurélien Paulmier, thesis director, LEGOS, Toulouse