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Demarcq, H., Reygondeau, G., Alvain, S., & Vantrepotte, V. (2012). Monitoring marine phytoplankton seasonality from space. Remote Sensing of Environment, 117, 211–222.
Résumé: Remote sensing techniques are used to study the large scale patterns related to the seasonal modes of variability of the marine phytoplankton. Ten years of monthly composite maps of sea surface chlorophyll-a concentration and the PHYSAT database of four Phytoplanktonic Functional Types (PFTs), both from SeaWiFS, are used to investigate characteristics of phytoplankton seasonality in the trades and westerlies wind oceanic biomes, where data density is adequate. We use a combination of wavelet transform and statistical techniques that allow us to quantify both intensity and duration of the seasonal oscillation of chlorophyll-a concentration and PFTs relative occurrence, and to map these relationships. Next, the seasonal oscillations detected are related to four PFTs revealing six major global phytoplanktonic associations. Our results elucidate the intensity and duration of the seasonal dynamic of the chlorophyll-a concentration and of the relative occurrence of four PFTs at a global scale. Thus, the typology of the different types of seasonality is investigated. Finally, an overall agreement between the results and the biogeochemical provinces partition proposed by Longhurst is found, revealing a strong environmental control on the seasonal oscillation of primary producers and a clear latitudinal organization in the succession of the phytoplankton types. Results provided in this study quantify the seasonal oscillation of key structural parameters of the global ocean, and their potential implications for our understanding of ecosystem dynamics.
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Dhurmeea, Z., Pethybridge, H., Langlais, C., Somes, C. J., Nikolic, N., Bourjea, J., et al. (2020). Spatial variation in stable isotopes and fatty acid trophic markers in albacore tuna (Thunnus alalunga) from the western Indian Ocean. Deep Sea Research Part I: Oceanographic Research Papers, , 103286.
Résumé: Albacore tuna (Thunnus alalunga) is a highly economically important species in the western Indian Ocean. However, knowledge of its ecological and nutritional characteristics, essential for proper management of the species, is lacking in the region. The trophodynamics of the Indian Ocean albacore was thus examined using known fatty acid trophic markers (FATMs) of primary producers, nutritional condition indices (NCIs) (omega-3/omega-6 ratio and total fatty acid content (TFA)), and baseline and lipid corrected stable isotope of carbon (δ13Ccorr) and nitrogen (δ15Ncorr), measured in the muscle tissue. We applied generalized additive mixed models to understand the spatiotemporal patterns and drivers of these tracers, taking into consideration several intrinsic and extrinsic variables: fish size, fishing position, month, chlorophyll-a and sea surface temperature (SST). Both chlorophyll-a and SST were significant as single explanatory variables for all tracers with SST being the best predictor for docosahexaenoic acid/eicosapentaenoic acid ratio, the omega-6 protists FATM, omega-3/omega-6 ratio, δ13Ccorr and δ15Ncorr. TFA was best predicted by fish size only. Higher primary productivity, as inferred by high δ13Ccorr values and diatom contribution, nutritional condition and trophic position, as inferred by high δ15Ncorr values, were observed in albacore from the temperate southern waters than in the northern tropical regions. Relationships between environmental variables and corrected stable isotopes, FATMs confirm that ocean warming and changes in primary productivity will impact nutrient flow and energy transfer in the marine food web which may have negative nutritional outcomes for albacore. This knowledge is particularly crucial in areas where oceanographic conditions and seawater temperatures are changing at a fast rate and should also be taken into consideration by fisheries managers.
Mots-Clés: Climate change; Environmental parameters; Phytoplankton; Trophodynamics
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Duboz, R., Versmisse, D., Travers, M., Ramat, E., & Shin, Y. - J. (2010). Application of an evolutionary algorithm to the inverse parameter estimation of an individual-based model. Ecological Modelling, 221, 840–849.
Résumé: Inverse parameter estimation of individual-based models (IBMs) is a research area which is still in its infancy, in a context where conventional statistical methods are not well suited to confront this type of models with data. In this paper, we propose an original evolutionary algorithm which is designed for the calibration of complex IBMs, i.e. characterized by high stochasticity, parameter uncertainty and numerous non-linear interactions between parameters and model output. Our algorithm corresponds to a variant of the population-based incremental learning (PBIL) genetic algorithm, with a specific “optimal individual” operator. The method is presented in detail and applied to the individual-based model OSMOSE. The performance of the algorithm is evaluated and estimated parameters are compared with an independent manual calibration. The results show that automated and convergent methods for inverse parameter estimation are a significant improvement to existing ad hoc methods for the calibration of IBMs.
Mots-Clés: algorithms; and; calibration; ecosystem; estimation; Evolutionary; genetic; Individual-based; marine; model; Parameter
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Follesa, M. C., Marongiu, M. F., Zupa, W., Bellodi, A., Cau, A., Cannas, R., et al. (2019). Spatial variability of Chondrichthyes in the northern Mediterranean. Sci. Mar., 83, 81–100.
Résumé: Thanks to the availability of the MEDITS survey data, a standardized picture of the occurrence and abundance of demersal Chondrichthyes in the northern Mediterranean has been obtained. During the spring-summer period between 2012 and 2015, 41 Chondrichthyes, including 18 sharks (5 orders and 11 families). 22 batoids (3 orders and 4 families) and 1 chimaera, were detected from several geographical sub-areas (GSAs) established by the General Fisheries Commission for the Mediterranean. Batoids had a preferential distribution on the continental shelf (10-200 m depth). while shark species were more frequent on the slope (200-800 m depth). Only three species, the Carcharhiniformes Galeus melastomus and Scyliorhinus canicida and the Torpediniformes Torpedo matmorata were caught in all GSAs studied. On the continental shelf, the Rajidae family was the most abundant, being represented in primis by Raja clavaia and then by R. miraleius, R. polystigma and R. asterias. The slope was characterized by the prevalence of G. melastomus in all GSAs, followed by S. canictda, E. spinax and Squalus blainville. Areas under higher fishing pressure, such as the Adriatic Sea and the Spanish coast (with the exception of the Balearic Islands), show a low abundance of chondrichthyans, but other areas with a high level of fishing pressure, such as southwestern Sicily, show a high abundance, suggesting that other environmental drivers work together with fishing pressure to shape their distribution. Results of generalized additive models highlighted that depth is one of the most important environmental drivers influencing the distribution of both batoid and shark species, although temperature also showed a significant influence on their distribution. The approach explored in this work shows the possibility of producing maps modelling the distribution of demersal chondrichthyans in the Mediterranean that are useful for the management and conservation of these species at a regional scale. However, because of the vulnerability of these species to fishing exploitation, fishing pressure should be further incorporated in these models in addition to these environmental drivers.
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Garrido, M., Cecchi, P., Vaquer, A., & Pasqualini, V. (2013). Effects of sample conservation on assessments of the photosynthetic efficiency of phytoplankton using PAM fluorometry. Deep-Sea Res. Part I-Oceanogr. Res. Pap., 71, 38–48.
Résumé: Pulse Amplitude Modulated (PAM) fluorometry is now a widely used method for the assessment of phytoplankton fitness, with an increasing popularity in field assessments. It is usually recommended to carry out measurements swiftly after collection, but the number of samples and analytical procedures needed to obtain valuable datasets sometimes makes immediate analysis impracticable, forcing delays between fluorescence measurements. Conservation conditions of samples before analysis may potentially affect their photosynthetic performances but no formal study documenting such impacts appears available in the literature. The aim of this study was to investigate the effects of storage conditions (temperature, duration) on photosynthetic parameters in different phytoplankton communities (characterized in situ by a BBE fluoroprobe) sampled during summer in different environmental locations in a Mediterranean lagoon (Biguglia lagoon, Corsica, France). PAM-fluorescence parameters were measured after three different conservation durations (2-4 h, 6-8 h and 10-12 h after collection) on samples stored at three different temperatures (15 degrees C, 25 degrees C and 35 degrees C). Results showed that storage at the highest temperature severely impacted photosynthetic parameters, with cumulative effects as storage duration increased. For phytoplankton samples collected in warm or tropical environments, storage at “room temperature” (25 degrees C) only appeared a valid option if measurements have to be carried out strictly within a very short delay. Inversely, cooling the samples (i.e. conservation at 15 degrees C) did not induce significant effects, independently of storage duration. Cooling appeared the best solution when sampling-to-analysis delay goes over a few hours. Long-term storage ( > 8 h) should definitively be avoided. (C) 2012 Elsevier Ltd. All rights reserved.
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