Simulated Abrupt Shifts in Aerobic Habitats of Marine Species in the Past, Present, and Future

• Published in: Earth's future Vol. 12; no. 4
• Main Authors: Fröb, Friederike, Bourgeois, Timothée, Goris, Nadine, Schwinger, Jörg, Heinze, Christoph
• Format: Journal Article
• Language: English
• Published: Bognor Regis John Wiley & Sons, Inc 01.04.2024; Wiley
• Subjects: abrupt shift; Ambient temperature; Atmospheric aerosols; Decomposition; Deoxygenation; Earth system model; Habitats; Hypoxia; Marine ecosystems; marine habitat; Metabolism; Ocean temperature; Ocean warming; Oceans; Oxygen; Oxygen demand; Partial pressure; Physiology; Sensitivity; Species; Temperature; Temperature tolerance; Thresholds; Time series; Upper ocean
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2023EF004141

The physiological tolerances of marine species toward ambient temperature and oxygen can jointly be evaluated in a single metric: the metabolic index. Changes therein characterize a changing aerobic habitat tailored to species‐specific thermal and hypoxia sensitivity traits. If the geographical limits of marine species as indicated by critical thresholds of the metabolic index shift abruptly in response to ocean warming and deoxygenation, aerobic habitat could potentially be lost abruptly. Here, we assess the spatio‐temporal detectability of abrupt shifts in potential habitats for selected marine species within the Shared Socioeconomic Pathway 5–8.5 (SSP5‐8.5) scenario run with the fully coupled Norwegian Earth System Model version 2 (NorESM2‐LM). We use an environmental time series changepoint detection routine and analyze the number and timing of these abrupt changes over the past, present and future. We construct nine ecophysiotypes with low, medium, and high resting vulnerability to hypoxia and sensitivity of hypoxia vulnerability to temperature, respectively, with six different thresholds for minimal oxygen demand. For all ecophysiotypes with positive temperature sensitivity to hypoxia, the volume of non‐viable habitat in the upper ocean expands between 1850 and 2100. Changepoints in the metabolic index are detected in 49.0 ± 9.2% of the volume that eventually becomes non‐viable for all ecophysiotypes over the course of the 21st century. More than 75% of these abrupt shifts occur in response to warming close to the surface, while at depth, the abrupt shifts driven by changes in oxygen partial pressure become more important, with potentially severe consequences for marine species, populations, and ecosystems. Plain Language Summary Future ocean warming and the accompanying deoxygenation will change the extent of habitats of all marine species. If the rate of future warming and deoxygenation is slow enough, marine species could adapt to the lower oxygen availability or migrate away to places that match their metabolic habitat requirements. However, if these rates are fast, and potentially exacerbated by abrupt shifts, the consequences for the future distribution of marine species will be profound. Here, we analyze abrupt shifts, or changepoints, in the metabolic index as a measure of metabolic habitat requirements for different marine species. Using projections of an Earth system model, we find that approximately half of the eventually lost habitat between 1850 and 2100 experiences abrupt shifts, and most of them occur between 1950 and 2040, mainly driven by the projected warming. Key Points Marine habitats described by the metabolic index are lost for a range of marine species in a strong emission scenario Abrupt changes in the metabolic index are detected in all ocean basins over a wide range of depth levels Temperature changes drive abrupt metabolic index changes close to the surface, while changes in oxygen become important at depth