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Periodic Report Summary 1 - MAREST (Marine Ecosystem Stability and Turnover)

Modern sea-level and climate changes have a strong potential to shift biological communities into novel states that have not present-day analogues, leaving ecologists with no observation basis to predict the likely biotic effects. The fossil record can offer examples of long-term biotic responses to past environmental changes, if portrayed in an appropriate time environmental framework.

Project MAREST applies an integrated field-based and analytical approach that combines for the first time sequence stratigraphy and palaeoecology – the core disciplines of Stratigraphic Palaeobiology - and geochemistry, to answer the following questions: (1) how do marine benthic communities respond to cyclic sea level changes? (2) Do communities continuously change through time or alternate intervals of stasis and turnover? (3) What is the relationship between the stratigraphic architecture and environmental perturbations that cause turnover? These questions are fulfilled through three main objectives: (1) to measure benthic community changes in the face of sea level change as detected from the sequence-stratigraphic architecture. (2) to reconstruct the niche evolution of fossil taxa through time; (3) to yield quantitative estimates of environmental gradients that control the turnover of benthic communities.
Whereas similar questions have been addressed for Palaeozoic and Caenozoic fauna, no attempt exists for the Mesozoic, a fundamental period in the history of life characterized by rapidly increasing ecospace utilization and biological diversification, and by the origin and radiation of the major groups that constitute modern marine ecosystems. Project MAREST focuses on the Middle-Upper Jurassic of the Western Interior (Sundance Seaway, USA) where macro-invertebrate rich, onshore-offshore sections, can be followed between and within third- and second order depositional sequences and parasequences.
Since the beginning of the project in January 2015, during the outgoing phase at the University of Georgia, progresses have been made in order to address objectives one and two, and research results of high quality have been produced and published in international conferences and journals. During two field seasons, quantitative abundance estimates were obtained from Middle-Upper Jurassic marine rocks at 44 localities in Wyoming, Montana and South Dakota. At each locality, stratigraphic columns were logged for lithology, bedding, sedimentary structures and trace fossils, in order to integrate palaeocological data within a sequence stratigraphic and environmental framework. Later, the statistical analysis of faunal data through diversity and ordination methods, allowed the reconstruction of benthic community changes through the 13 myr history of the Seaway.
The main results achieved so far show that (i) Seaway communities were characterised by low richness and high dominance relative to most areas globally in the Jurassic, and this was driven by steep temperature and salinity gradients along the length of the Seaway that hindered colonization of species from the open ocean. (ii) A main faunal turnover occurred at the Middle–Upper Jurassic transition, which coincided with a change from carbonate to siliciclastic depositional systems. This was initiated by northward drift of the North American Plate, which moved the area from subtropical latitudes to more humid temperate latitudes, and by global cooling. (iii) Turnover was not uniform across the onshore–offshore gradient, but was higher in offshore environments. The higher resilience of onshore communities to third-order sea-level fluctuations and to the change from a carbonate to a siliciclastic system was driven by eurytopic species that persisted from the opening to the closing of the Seaway. Lower stability in offshore facies was instead controlled by the presence of more volatile stenotopic species.
These results highlight: (i) the need for ecological studies to complement taxonomic studies of macroevolutionary events, because estimates based on an ecological analysis of relative abundance patterns contrast with taxonomic-based approaches, which show instead onshore increase in taxonomic turnover rates. (ii) The importance of a stratigraphic palaeobiological approach for understanding the link between environmental and faunal gradients, and for understanding the long-term changes in these gradients over time that produce the local stratigraphical pattern of changes in community composition.

During the next phase of the project (incoming phase: January-December 2017), at Plymouth University, objective three will be addressed by reconstructing temperature and salinity gradients in the Seaway through the analysis of stable isotope and trace elements of unaltered calcitic mollusc shells collected in the Seaway. This will allow to understand the relationship between changes in community composition and environmental factors, building a bridge between Stratigraphic Palaeobiology and geochemical studies. Stable isotope and trace element analyses from fossil shells are among the most used techniques to reconstruct past climate changes, and their application to the Mesozoic is widespread however no case-studies exist so far that link qualitatively and quantitatively faunal and multiple environmental proxy changes.
Project MAREST will provide a significant contribution to our understanding of the response of shallow water marine ecosystems to sea level and climate changes, a topic relevant to the European Research Area, as shown by the 2013 working document "An EU strategy on adaptation to climate change", focused on the impacts of climate changes on coastal zones.
On the project website ( updates and news on the progress of MAREST are available.

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United Kingdom


Life Sciences
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