Quantifying deep-water marine ecospace utilization andecosystem engineering from late Permian to Middle Triassic

Abstract

<p indent=0mm>With the loss of around three-fourths of marine and continental genera, the end-Permian mass extinction (EPME) event was the biggest biotic crisis in the Phanerozoic era. The shallow marine and continental ecosystem were almost collapsed due to continuous harsh and turbulent environment, e.g., global warming and anoxic event. However, the overall response strategies of biotic communities and function of marine ecosystem engineering are still uncertain. As a promising window for understanding organism-environmental interactions, trace fossils not only record the response of soft-bodied animals that are not easily preserved as fossils to the mass extinction event, but also record a large number of complex behaviors involving the construction of ecosystems, and document the entire process of the collapse and recovery of marine ecosystems during the Permian-Triassic transition. A global Permian-Triassic deep-water marine database was compiled on the basis of literatures and personal data. The total number of invertebrate ichnogenera identified as valid is 62 from a survey of 146 Permian-Triassic stratigraphic unites. Ichnodiversity simply refers to the number of ichnotaxa present at ichnogenus level. Ichnodisparity is a measure of the variability of morphological plans in trace fossils, which reveals major innovations in body plan, locomotive system, and behavioral program. The multidimensional ecospace utilization and ecosystem engineering schemes based on body fossils have been adapted for trace fossils. Ecospace utilization is quantified on the basis of the number of modes of life, following three parameters: Tiering (subdivided into surficial, semi-infaunal, shallow, intermediate and deep tiers), motility (subdivided into motile, facultatively motile and non-motile types), and feeding mode (subdivided into suspension feeding, non-specialized deposit feeding, specialized deposit feeding, predation and others). Ecosystem engineering is categorized on the basis of three parameters: Tiering (as described above), mode of sediment interaction (intrusion, compression, backfilling and excavation), and mode of sediment modification (biodiffusion, conveyors, regenerators, and gallery biodiffusion). Ecosystem engineering impact (EEI) values and ranges on the basis of three parameters: (1) Tiering (surficial tier, semi-infaunal tier, shallow tier, intermediate tier, and deep tier); (2) bioirrigation potential (improbable, probable, and possible); and (3) potential functional group, describing how substrate is modified by burrowing organisms (biodiffusion, conveyors, regenerators, and gallery biodiffusion). This paper aims to understand the patterns of EPME on the marine deep-water ecospace utilization and ecosystem engineering, and the adaptation and modification mechanism of organisms in the Early Triassic deep-water ecosystem recovery from an ecological perspective. Our results show that in the Permian-Triassic transition, ichnodiversity, ichnodisparity, bioturbation index, the ecospace utilization and ecosystem engineering cubes of deep-water marine were not significantly declined, indicating that the marine deep-water ecosystem was under relatively stable conditions during the EPME. Non-specialized deposit feeding, motile, gallery biodiffusion and compression were the most common ecosystem engineers. Notably, gallery biodiffusion, as the highest impact sediment modification functional group, is present through the transition of Permian-Triassic. Modes of life in the Early and Middle Triassic tend to be diversified and dominated by the backfilling-conveyors in the shallow tiering. Increased bioirrigation further affected the geochemical cycle of the substrate in the Early Triassic and laid the foundation the further construction and development of deep tiering ecospace utilization. In the Middle Triassic, the nutrient deep-tiering ecospace was inhabited by organisms with advanced bioirrigation capacities.