Marine ecosystem resilience during extreme deoxygenation: the Early Jurassic oceanic anoxic event

Abstract

Global warming during the Early Jurassic, and associated widespread ocean deoxygenation, was comparable in scale with the changes projected for the next century. This study quantifies the impact of severe global environmental change on the biological traits of marine communities that define the ecological roles and functions they deliver. We document centennial-millennial variability in the biological trait composition of Early Jurassic (Toarcian) seafloor communities and examine how this changed during the event using biological traits analysis. Environmental changes preceding the global oceanic anoxic event (OAE) produced an ecological shift leading to stressed benthic palaeocommunities with reduced resilience to the subsequent OAE. Changes in traits and ecological succession coincided with major environmental changes; and were of similar nature and magnitude to those in severely deoxygenated benthic communities today despite the very different timescales. Changes in community composition were linked to local redox conditions whereas changes in populations of opportunists were driven by primary productivity. Throughout most of the OAE substitutions by tolerant taxa conserved the trait composition and hence functioning, but periods of severe deoxygenation caused benthic defaunation that would have resulted in functional collapse. Following the OAE recovery was slow probably because the global nature of the event restricted opportunities for recruitment from outside the basin. Our findings suggest that future systems undergoing deoxygenation may initially show functional resilience, but severe global deoxygenation will impact traits and ecosystem functioning and, by limiting the species pool, will slow recovery rates.

Ocean warming affected faunal dynamics of benthic invertebrate assemblages across the Toarcian Oceanic Anoxic Event in the Iberian Basin (Spain)

“…This difference could be due to the magnitude and prolonged duration of raised temperatures in our study system or because increases in temperature need not be deleterious as long as organisms shift towards or stay close to their thermal optima. Our observation of functional shifts at the onset of the TOAE is consistent with the timing of functional changes in dysoxic to anoxic settings [28,29,31,89]. However, apart from functional change, these dysoxic-anoxic environments also exhibit compositional shifts at the onset of the TOAE negative carbon isotopic excursion.…”

“…The latest phase of the TOAE is characterized by a swift recovery of both taxonomical and ecological biodiversity. Such a geologically quick recovery contrasts with other areas where the TOAE is characterized by black shales (e.g., [28,29,31,89]) and has been related to the more favourable conditions of Tethyan areas where anoxia and dysoxia did not develop [9]. The return to high diversity values in the latest TOAE is synchronous with the shift to more positive δ 18 O values, with cooler temperatures indicating the end of the hyperthermal interval.…”

Ecological functioning of mudflats: global analysis reveals both regional differences and widespread conservation of functioning

“…Major localised threats for mudflats include coastal urbanisation, dredging, land reclamation and diffuse and point source pollution (e.g. Frid & Caswell 2017), which occur against a backdrop of global climate change (IPCC 2013, van der Wegen et al 2017.…”

Advances in the understanding of the Toarcian Oceanic Anoxic Event (IGCP-655 annual report)

“…There are significant advances on the incidence of the T-OAE on the macroinvertebrate communities (e.g., Baeza-Carratalá et al, 2017;Caswell and Frid, 2017;Martindale and Aberhan, 2017;Monarrez et al, 2017;Posenato et al, 2017). Brachiopods and bivalves have been the main studied groups.…”