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1. Quantifying paleoecological impact of the OAE1a on shallow marine ecosystems from southeastern France

   https://doi.org/10.1016/j.sedgeo.2024.106757  

   Godet, Alexis; Byerly, Jacob; Bourdon, Matthew; Suarez, Marina (November 2024, Sedimentary Geology)

   Climate and environmental instability during the early Aptian culminated with the unfolding of the Oceanic Anoxic Event (OAE) 1a, which resulted in the deposition of black shales in deep marine settings and a typical negative spike followed by a positive excursion in δ13C values. In Vercors (southern France) the Urgonian platform developed prior to and coeval to the OAE1a, but the impact of this paleoenvironmental crisis on the ecology of benthic ecosystems is yet to be quantified. We gathered field and petrographic data to identify sequence boundaries and maximum flooding surfaces that are biostratigraphically dated and correlated between four localities within the study area. A composite δ13C curve is built where the C3 to C7 isotope segments from the literature are identified, pinpointing the onset of the OAE1a above the last episode of deposition of Urgonian facies rich in rudist bivalves. Furthermore, thin section point counting data are used to quantify the proportion of allochems in samples and to trace changes in the ecology of ecosystems. The principal component analysis of point counting data helps define ecological tiers: a diversified, photozoan association with rudists, green algae, and benthic foraminifera dominated ecosystems before the OAE1a and up to the C7 segment, while a less diversified heterozoan association with bryozoans and crinoids developed after the OAE1a. To explore the triggers for this change, the principal component analysis of elemental geochemical data highlights an increased nutrient and detrital input as major triggering mechanisms for ecological adjustments and changes in the biodiversity of ecosystems. In particular after the OAE1a, an increase in detrital and nutrient input leads to the replacement of photozoan by heterozoan assemblages more adapted to these stressful conditions. This research directly links paleoenvironmental deterioration to paleoecological changes and quantifies the amount of adaptation of ecosystems. 

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2. The response of Corbières carbonate platform to Early Cretaceous super greenhouse conditions

   Sharpe, Justin; Sansing, Alexis; Suarez, Marina; Godet, Alexis (May 2024, SEPM)

   Shallow marine reef systems are the most diversified ecosystems of modern oceans but face a severe threat from climate change: 91% of ecosystems in the Great Barrier Reef suffer from coral bleaching. To better understand how such ecosystems cope with environmental stress, a carbonate platform from the Corbières region of southern France serves as ancient analog as it developed during the Early Aptian OAE1a, a period marked by significant climate and volcanic activity. The study sought to uncover how benthic carbonate-producing ecosystems adapted during this challenging period. The OAE1a is typically identified by distinctive shifts in carbon isotope composition (δ13C) values and increased organic matter preservation in deep marine settings. Identifying these shifts can shed light on factors favoring carbonate production. The research proposes that warm, arid climates promoted reduced continental weathering and limited transfer of siliciclastic particles and dissolved nutrients that might enhance carbonate platform resilience. We identified seven out of eight segments of the OAE1a and specific microfacies in the Corbières region. Prior to the OAE1a, carbonate production was sustained by a photozoan assemblage with rudists and [insert main biota], with no changes in fauna and flora. A significant shift occurred at the interface between the Urgonian Marl that consists of siliciclastic-rich deposits with bryozoan and crinoid, indicating platform drowning and altered carbonate production. In the aftermaths of the OAE1a, carbonate production not only rebounded but thrived in the upper Urgonian Marl and Urgonian 2 with the return of a photozoan assemblage. This research provides an understanding into the adaptability of carbonate ecosystems to environmental stress, potentially offering lessons for mitigating similar crisis in the future. 

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3. Pentaradial eukaryote suggests expansion of suspension feeding in White Sea-aged Ediacaran communities

   https://doi.org/10.1038/s41598-021-83452-1  

   Cracknell, K; García‑Bellido, D.C.; Gehling, J.G.; Ankor, M.J.; Darroch, S.A.F.; Rahman, I.A. (February 2021, Scientific reports)

   null (Ed.)

   Suspension feeding is a key ecological strategy in modern oceans that provides a link between pelagic and benthic systems. Establishing when suspension feeding first became widespread is thus a crucial research area in ecology and evolution, with implications for understanding the origins of the modern marine biosphere. Here, we use three-dimensional modelling and computational fluid dynamics to establish the feeding mode of the enigmatic Ediacaran pentaradial eukaryote Arkarua. Through comparisons with two Cambrian echinoderms, Cambraster and Stromatocystites, we show that flow patterns around Arkarua strongly support its interpretation as a passive suspension feeder. Arkarua is added to the growing number of Ediacaran benthic suspension feeders, suggesting that the energy link between pelagic and benthic ecosystems was likely expanding in the White Sea assemblage (~ 558–550 Ma). The advent of widespread suspension feeding could therefore have played an important role in the subsequent waves of ecological innovation and escalation that culminated with the Cambrian explosion. 

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4. Biogeography and ecology of Ostracoda in the U.S. northern Bering, Chukchi, and Beaufort Seas

   https://doi.org/10.1371/journal.pone.0251164  

   Gemery, Laura; Cronin, Thomas M.; Cooper, Lee W.; Dowsett, Harry J.; Grebmeier, Jacqueline M. (May 2021, PLOS ONE)

   Frontalini, Fabrizio (Ed.)

   Ostracoda (bivalved Crustacea) comprise a significant part of the benthic meiofauna in the Pacific-Arctic region, including more than 50 species, many with identifiable ecological tolerances. These species hold potential as useful indicators of past and future ecosystem changes. In this study, we examined benthic ostracodes from nearly 300 surface sediment samples, >34,000 specimens, from three regions—the northern Bering, Chukchi and Beaufort Seas—to establish species’ ecology and distribution. Samples were collected during various sampling programs from 1970 through 2018 on the continental shelves at 20 to ~100m water depth. Ordination analyses using species’ relative frequencies identified six species, Normanicythere leioderma , Sarsicytheridea bradii , Paracyprideis pseudopunctillata , Semicytherura complanata , Schizocythere ikeyai , and Munseyella mananensis , as having diagnostic habitat ranges in bottom water temperatures, salinities, sediment substrates and/or food sources. Species relative abundances and distributions can be used to infer past bottom environmental conditions in sediment archives for paleo-reconstructions and to characterize potential changes in Pacific-Arctic ecosystems in future sampling studies. Statistical analyses further showed ostracode assemblages grouped by the summer water masses influencing the area. Offshore-to-nearshore transects of samples across different water masses showed that complex water mass characteristics, such as bottom temperature, productivity, as well as sediment texture, influenced the relative frequencies of ostracode species over small spatial scales. On the larger biogeographic scale, synoptic ordination analyses showed dominant species— N . leioderma (Bering Sea), P . pseudopunctillata (offshore Chukchi and Beaufort Seas), and S . bradii (all regions)—remained fairly constant over recent decades. However, during 2013–2018, northern Pacific species M . mananensis and S . ikeyai increased in abundance by small but significant proportions in the Chukchi Sea region compared to earlier years. It is yet unclear if these assemblage changes signify a meiofaunal response to changing water mass properties and if this trend will continue in the future. Our new ecological data on ostracode species and biogeography suggest these hypotheses can be tested with future benthic monitoring efforts. 

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5. Intraspecific variation and energy channel coupling within a Chilean kelp forest

   https://doi.org/10.1002/ecy.3198  

   Elliott Smith, E; Harrod, C; Docmac, F; Newsome, S. (October 2020, Ecology)

   Winemiller, KO. (Ed.)

   The widespread importance of variable types of primary production, or energy channels, to consumer communities has become increasingly apparent. However, the mechanisms underlying this “multichannel” feeding remain poorly understood, especially for aquatic ecosystems that pose unique logistical constraints given the diversity of potential energy channels. Here, we use bulk tissue isotopic analysis along with carbon isotope (δ13C) analysis of individual amino acids to characterize the relative contribution of pelagic and benthic energy sources to a kelp forest consumer community in northern Chile. We measured bulk tissue δ13C and δ15N for >120 samples; of these we analyzed δ13C values of six essential amino acids (EAA) from nine primary producer groups (n = 41) and 11 representative nearshore consumer taxa (n = 56). Using EAA δ13C data, we employed linear discriminant analysis (LDA) to assess how distinct EAA δ13C values were between local pelagic (phytoplankton/particulate organic matter), and benthic (kelps, red algae, and green algae) endmembers. With this model, we were able to correctly classify nearly 90% of producer samples to their original groupings, a significant improvement on traditional bulk isotopic analysis. With this EAA isotopic library, we then generated probability distributions for the most important sources of production for each individual consumer and species using a bootstrap‐resampling LDA approach. We found evidence for multichannel feeding within the community at the species level. Invertebrates tended to focus on either pelagic or benthic energy, deriving 13–67% of their EAA from pelagic sources. In contrast, mobile (fish) taxa at higher trophic levels used more equal proportions of each channel, ranging from 19% to 47% pelagically derived energy. Within a taxon, multichannel feeding was a result of specialization among individuals in energy channel usage, with 37 of 56 individual consumers estimated to derive >80% of their EAA from a single channel. Our study reveals how a cutting‐edge isotopic technique can characterize the dynamics of energy flow in coastal food webs, a topic that has historically been difficult to address. More broadly, our work provides a mechanism as to how multichannel feeding may occur in nearshore communities, and we suggest this pattern be investigated in additional ecosystems. 

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