246 / 2024-09-12 16:23:17

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

climate change, ENSO, marine aerobic habitat, South East Pacific

Session 15 - Ocean deoxygenation: drivers, trends, and biogeochemical-ecosystem impacts

The oceans are warming at unprecedented rates and as a consequence they are losing oxygen. The consequences on marine ecosystems are already observed, with rapid poleward shifts of pelagic organisms and profound transformations of ecosystems, attributed to ocean warming.

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. The impact of climate change (CC) on the SEP marine organisms has been weakly studied. If CC impacts the SEP, it is also subjected to the largest climatic mode, the El Niño Southern Oscillation (ENSO). ENSO profoundly impacts the SEP environment by modulating oxygen and temperature levels, but how it impacts marine aerobic habitat around key areas of the SEP remains unclear.

Therefore, our goal here is to assess the pressure CC and ENSO exert on marine organisms in the future climate. We use climatic velocities of the metabolic index and Pcrit, which accounts for minimal metabolic demand, 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 aerobic scope and 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. Eastern Pacific El Niño events marginally compensate for the deoxygenation trends in remote areas of the seamounts. These changes in habitat suitability and in particular the differences between the epipelagic and mesopelagic realms, could have profound implications at the ecosystem level, triggering a recomposition and reorganisation of fish populations. This poses additional challenges for the design of Marine Protected Areas such as considering the whole trophic chains and 3D habitat of target species.