354-4 The Effects of Anoxia on Panthalassan Food Web Stability during the Late Triassic

Abstract:

Anoxia ranks among the most widespread deleterious anthropogenic effects on modern marine ecosystems, and ancient analogues are critical for forecasting their resilience. The geological record provides crucial context for understanding the long-term effects of recurring anoxia on food web stability. The Late Triassic was an interval of prolonged extinction characterized by a series of stepwise biotic turnovers that culminated in the end-Triassic mass extinction (ETME). These biotic crises are heavily associated with anoxia, prompted by massive volcanic eruptions from the Central Atlantic Magmatic Province, which may have significantly destabilized marine communities. Here, we examine marine food webs from the Norian and Rhaetian stages to determine how anoxia may have impacted food web stability prior to the ETME. To quantify these impacts on ecosystem stability, we analyzed the network structure of these food webs, specifically focusing on modules and modularity. In food webs, modules act as structural compartments of heavily interacting species. High modularity increases ecosystem resilience because these compartments act as buffers, preventing local secondary extinctions from cascading across the entire network. We assessed the number of modules and modularity in food webs reconstructed from fossil assemblages found in the Gabbs Formation in the Muller and New York Canyons (west-central Nevada, USA).

Food web links were assigned based on the potential for consumer-resource interactions for 154 taxa in the Norian and 67 taxa in the Rhaetian. The Norian food web has a higher modularity of 0.382 and consists of four modules: (1) a detritivore module, (2) a grazer module, (3) a bacteriovore module, and (4) a carnivore module. During the Rhaetian, this structure collapsed to a lower modularity of 0.098 and two modules: (1) a detritivore module and (2) a bacteriovore module. This decrease is likely due to extinctions driven by anoxia, which also resulted in the loss of associated interactions among taxa—producing a sparser, less connected food web. These structural changes suggest that anoxia significantly destabilized marine food webs across the Norian–Rhaetian boundary. If modules are an important feature of stable marine ecosystems that can be disrupted by anoxia, this study would provide critical insights for modern conservation by using the breakdown of specific modules as an early warning indicator for ecosystems currently facing severe oxygen depletion.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.