%0 Journal Article %J Nature Climate Change %D 2019 %T Temperature patterns and mechanisms influencing coral bleaching during the 2016 El Niño %A McClanahan, T.R. %A Darling, E.S. %A Maina, J.M. %A Muthiga, N.A. %A D’agata, S. %A Jupiter, S.D. %A Arthur, R. %A Wilson, S.K. %A Mangubhai, S. %A Nand, Y. %A Ussi, A.M. %A Humphries, A.T. %A Patankar, V.J. %A Mireille M.M. Guillaume %A Philippe Keith %A Shedrawi, G. %A Julius, P. %A Grimsditch, G. %A Ndagala, J. %A Leblond, J. %K Algae %K Anthozoa %X Under extreme heat stress, corals expel their symbiotic algae and colour (that is, ‘bleaching’), which often leads to widespread mortality. Predicting the large-scale environmental conditions that reinforce or mitigate coral bleaching remains unresolved and limits strategic conservation actions1,2. Here we assessed coral bleaching at 226 sites and 26 environmental variables that represent different mechanisms of stress responses from East Africa to Fiji through a coordinated effort to evaluate the coral response to the 2014–2016 El Niño/Southern Oscillation thermal anomaly. We applied common time-series methods to study the temporal patterning of acute thermal stress and evaluated the effectiveness of conventional and new sea surface temperature metrics and mechanisms in predicting bleaching severity. The best models indicated the importance of peak hot temperatures, the duration of cool temperatures and temperature bimodality, which explained 50% of the variance, compared to the common degree-heating week temperature index that explained only 9%. Our findings suggest that the threshold concept as a mechanism to explain bleaching alone was not as powerful as the multidimensional interactions of stresses, which include the duration and temporal patterning of hot and cold temperature extremes relative to average local conditions. © 2019, The Author(s), under exclusive licence to Springer Nature Limited. %B Nature Climate Change %V 9 %P 845-851 %G eng %U https://www.nature.com/articles/s41558-019-0576-8 %R 10.1038/s41558-019-0576-8 %0 Journal Article %J Progress in Oceanography %D 2018 %T Plankton food-web functioning in anthropogenically impacted coastal waters (SW Mediterranean Sea): An ecological network analysis %A Meddeb, M. %A Grami, B. %A Chaalali, A. %A Haraldsson, M. %A Nathalie Niquil %A Pringault, O. %A Sakka Hlaili, A. %K Algae %K anthropogenic effect %K Anthropogenic impacts %K Anthropogenic pressures %K Bizerte %K Bizerte Bay %K Chemical analysis %K Chemical contamination %K coastal water %K community structure %K Ecological network analysis %K Ecology %K ecosystem function %K ecosystem modeling %K Ecosystems %K eutrophication %K food web %K Food webs %K Functional properties %K Inverse problems %K Lakes %K Linear inverse models %K Markov processes %K Mediterranean coastal waters %K Mediterranean ecosystem %K Mediterranean sea %K Monte Carlo methods %K network analysis %K Phytoplankton %K Plankton %K primary production %K Tunisia %K Zooplankton %X The study is the first attempt to (i) model spring food webs in three SW Mediterranean ecosystems which are under different anthropogenic pressures and (ii) to project the consequence of this stress on their function. Linear inverse models were built using the Monte Carlo method coupled with Markov Chains to characterize the food-web status of the Lagoon, the Channel (inshore waters under high eutrophication and chemical contamination) and the Bay of Bizerte (offshore waters under less anthropogenic pressure). Ecological network analysis was used for the description of structural and functional properties of each food web and for inter-ecosystem comparisons. Our results showed that more carbon was produced by phytoplankton in the inshore waters (966–1234 mg C m−2 d−1) compared to the Bay (727 mg C m−2 d−1). The total ecosystem carbon inputs into the three food webs was supported by high primary production, which was mainly due to >10 µm algae. However, the three carbon pathways were characterized by low detritivory and a high herbivory which was mainly assigned to protozooplankton. This latter was efficient in channelling biogenic carbon. In the Lagoon and the Channel, foods webs acted almost as a multivorous structure with a tendency towards herbivorous one, whereas in the Bay the herbivorous pathway was more dominant. Ecological indices revealed that the Lagoon and the Channel food webs/systems had high total system throughput and thus were more active than the Bay. The Bay food web, which had a high relative ascendency value, was more organized and specialized. This inter–ecosystem difference could be due to the varying levels of anthropogenic impact among sites. Indeed, the low value of Finn's cycling index indicated that the three systems are disturbed, but the Lagoon and the Channel, with low average path lengths, appeared to be more stressed, as both sites have undergone higher chemical pollution and nutrient loading. This study shows that ecosystem models combined with ecological indices provide a powerful approach to detect change in environmental status and anthropogenic impacts. © 2018 %B Progress in Oceanography %I Elsevier Ltd %V 162 %P 66-82 %G eng %U https://www.sciencedirect.com/science/article/abs/pii/S0079661117300782 %R 10.1016/j.pocean.2018.02.013 %0 Journal Article %J Journal of Marine Science and Technology %D 2014 %T Evolution of Vacuolar Pyrophosphatases and Vacuolar H+-Atpases in Diatoms %A Adrien Bussard %A Pascal Jean Lopez %K Algae %K endoplasmic reticulum %K H^+-PPases %K V-ATPases %K vacuole %X

To cope with changing environments and maintain optimal metabolic conditions, the control of the intracellular proton gradients has to be tightly regulated. Among the important proton pumps, vacuolar H^+-ATPases (V-ATPases) and H^+-translocating pyrophosphatases (H^+-PPases) were found to be involved in a number of physiological processes, and shown to be regulated at the expression level and to exhibit specific sub-cellular localizations. Studies of the role of these transporters are relatively scarce in algae and nearly absent in diatoms. Phylogenetic analyses disclose that diatoms, with both K^+-dependent and K^+-independent membrane integral pyrophosphatases, including proteins with high homology with a novel class of Na^+,H^+-PPases. Analyses of Phaeodactylum tricornutum EST libraries show that the gene putatively encoding a Na^+,H^+-PPase is over-expressed in urea adapted condition. Genome-wide investigations of the reservoir of V-ATPases encoding subunits demonstrate that diatoms display an expended number of genes encoding for the proteolipid subunits c of the V0 subcomplex. Preliminary localization studies show that one of V0-c subunits is associated to the endoplasmic reticulum membrane in P. tricornutum. Altogether our data highlight that the combination of comparative and functional genomic approaches reach promises to provide new information to the roles of membrane proton pumps in diatoms.

%B Journal of Marine Science and Technology %V 22 %P 50-59 %8 Feb %G eng %R 10.6119/JMST-013-0829-1