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Post-extinction recovery of the Phanerozoic oceans and biodiversity hotspots

Pedro Cermeño, Carmen García-Comas, Alexandre Pohl,  Simon Williams, Michael J. Benton, Chhaya Chaudhary, Guillaume Le Gland, R. Dietmar Müller, Andy Ridgwell & Sergio M. Vallina 


The fossil record of marine invertebrates has long fuelled the debate as to whether or not there are limits to global diversity in the sea. Ecological theory states that, as diversity grows and ecological niches are filled, the strengthening of biological interactions imposes limits on diversity. However, the extent to which biological interactions have constrained the growth of diversity over evolutionary time remains an open question. Here we present a regional diversification model that reproduces the main Phanerozoic eon trends in the global diversity of marine invertebrates after imposing mass extinctions. We find that the dynamics of global diversity are best described by a diversification model that operates widely within the exponential growth regime of a logistic function. A spatially resolved analysis of the ratio of diversity to carrying capacity reveals that less than 2% of the global flooded continental area throughout the Phanerozoic exhibits diversity levels approaching ecological saturation. We attribute the overall increase in global diversity during the Late Mesozoic and Cenozoic eras to the development of diversity hotspots under prolonged conditions of Earth system stability and maximum continental fragmentation. We call this the ‘diversity hotspots hypothesis’, which we propose as a non-mutually exclusive alternative to the hypothesis that the Mesozoic marine revolution led this macroevolutionary trend.

Respirometric assessment of bacterial kinetics in algae-bacteria and activated sludge processes

A.Sánchez-Zurano, S.Rossi, J.M.Fernández-Sevilla, G.Acién Fernández, E.Molina-Grima, E.Ficara


Algae-bacteria (AB) consortia can be exploited for effective wastewater treatment, based on photosynthetic oxygenation to reduce energy requirements for aeration. While algal kinetics have been extensively evaluated, bacterial kinetics in AB systems are still based on parameters taken from the activated sludge models, lacking an experimental validation for AB consortia. A respirometric procedure was therefore proposed, to estimate bacterial kinetics in both activated sludge and AB, under different conditions of temperature, pH, dissolved oxygen, and substrate availability. Bacterial activities were differently influenced by operational/environmental conditions, suggesting that the adoption of typical activated sludge parameters could be inadequate for AB modelling. Indeed, respirometric results show that bacteria in AB consortia were adapted to a wider range of conditions, compared to activated sludge, confirming that a dedicated calibration of bacterial kinetics is essential for effectively modelling AB systems, and respirometry was proven to be a powerful and reliable tool to this purpose.

Profiling microalgal cultures growing on municipal wastewater and fertilizer media in raceway photobioreactors

ElisaClagnan, GiulianaD’Imporzano, MartaDell’Orto, AnaSanchez-Zurano, Francisco GabrielAcién-Fernandez, BiancamariaPietrangeli, FabrizioAdani


Microalgae cultivation is proposed as an effective system for pathogens reduction and wastewater depuration, however, a full characterisation of the risks is still needed. Two raceways were inoculated with Scenedesmus, one using wastewater and the other using a fertilizer medium. Microbial community and pathogen presence were explored by next generation sequencing (NGS), commercial qPCR array and plate counts. These methods proved to be complementary for a full characterization of community structure and potential risks.

Media and sampling locations contributed to shape communities and pathogenic loads. The main pathogenic genera detected were Arcobacter and Elizabethkingia (mainly in wastewater) with an important presence of Aeromonas (all samples). A lower presence of pathogens was detected in fertilizer samples, while wastewater showed a reduction from inlet to outlet. Raceways showed potential as an effective biotreatment, with most of the retained pathogens released in the outlet and only a minor part settled in the biomass.

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