Two decades of oligotrophication: Evidence for a phytoplankton community shift in the coastal lagoon of Thau (Mediterranean Sea, France)

Derolez, Valérie; Soudant, Dominique; Malet, Nathalie; Chiantella, Claude; Richard, Marion; Abadie, Éric; Aliaume, Catherine; Bakhouche, Béatrice

doi:10.1016/j.ecss.2020.106810

Cited by 40 publications

(48 citation statements)

References 73 publications

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“…From 1972 to 1993, DIP was analysed in water samples collected monthly in summer at ZA station, located in the shellfish farming area in the north-east part of the lagoon (Fig. 1A) (Collos et al, 2009;Derolez et al, 2020;Souchu et al, 1998).…”

Section: Hydrological Nutrients and Phytoplankton Time Seriesmentioning

confidence: 99%

“…Our results, based on long time series, show that the pelagic and benthic communities in Thau lagoon changed during the course of oligotrophication. Previous studies of the lagoon from the 1990s to the 2000s showed that the gradual decrease in nutrient inputs from the watershed resulted in a continuous decrease in nutrients and Chl a concentrations in the water column (Collos et al, 2009;Derolez et al 2020;Deslous-Paoli et al, 1998;Gowen et al, 2015). Our study revealed the continuation of oligotrophication over the past 20 years (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018), and the recovery of the ecosystem, through nutrient and phytoplankton parameters.…”

Section: Ecological Changes and Regime Shifts During Oligotrophicationmentioning

confidence: 99%

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Fifty years of ecological changes: Regime shifts and drivers in a coastal Mediterranean lagoon during oligotrophication

Derolez

Malet

Fiandrino

et al. 2020

Science of The Total Environment

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Thau lagoon is a large Mediterranean coastal lagoons and it supports traditional shellfish farming activities. It has been subject to eutrophication leading to major anoxic events associated with massive mortalities of shellfish stocks. Since the 1970s, improvements have been made to wastewater treatment systems, which have gradually led to oligotrophication of the lagoon. The aim of our study was to determine how the decrease in nutrient inputs resulted in major ecological changes in Thau lagoon, by analysing five decades of time-series of observations on pelagic and benthic autotrophic communities. We were able to identify two periods during the oligotrophication process. Period 1 was considered a eutrophic period, characterised by the shift from seagrass dominance to dominance of red macroalgae. Period 2 (1993-2018), characterised by improved eutrophication status, was further divided into three: a transition phase (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003) during which the water column continued to recover but the benthic community lagged behind in recovery and in partial resilience; a regime shift (2003)(2004)(2005)(2006), after which the water column became oligotrophic and seagrass began to recover (2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018). Considering anoxia crises as indicators of ecosystem resilience and resistance, we used a generalised linear model to analyse meteorological and environmental data with the aim of identifying the triggers of summer anoxia over the study period. Among the meteorological variables studied, air temperature had the strongest positive effect, followed by the period and wind intensity (both negative effects) and by rainfall in July (positive effect). The risk of triggering anoxia was lower in period 2, evidence for the increasing resistance of the ecosystem to climatic stress throughout the oligotrophication process. At the ecosystem scale and in the long term perspective, the ecological gains related to oligotrophication are especially important in the context of climate change, with more frequent and severe heat waves predicted.Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.

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Section: Hydrological Nutrients and Phytoplankton Time Seriesmentioning

confidence: 99%

Section: Ecological Changes and Regime Shifts During Oligotrophicationmentioning

confidence: 99%

Fifty years of ecological changes: Regime shifts and drivers in a coastal Mediterranean lagoon during oligotrophication

Derolez

Malet

Fiandrino

et al. 2020

Science of The Total Environment

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“…In this context, as studies of experimental warming are scarcer during fall, the autumnal in situ plankton community of the coastal Mediterranean Thau Lagoon was investigated. Thau Lagoon is connected by channels to the Mediterranean sea, and has a salinity varying from 29.6 to 40.8 (Derolez et al 2020b). This lagoon is rather shallow, with a mean depth of 4 m, and therefore is experiencing a great range of temperature variations through the year (Trombetta et al 2019).…”

Section: Introductionmentioning

confidence: 99%

“…The nanophytoplankton, which can dominate the phytoplankton community in term of biomass (Trombetta et al 2019), is characterised by cryptophytes, chrysophytes and prymnesiophytes (Bec et al 2011;Trombetta et al 2019). Microphytoplankton are mainly represented by diatoms and dinoflagellates are generally less abundant, excepted during exceptional blooms (Derolez et al 2020b). Thus, the phytoplankton community of Thau Lagoon is generally dominated by small phytoplankton (Trombetta et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Effects of experimental warming on small phytoplankton, bacteria and viruses in autumn in the Mediterranean coastal Thau Lagoon

et al. 2021

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To investigate the responses of a natural microbial plankton community of coastal Mediterranean waters to warming, which are still poorly known, an in situ mesocosm experiment was carried out in Thau Lagoon during autumn 2018. Several microorganisms, including virio-, bacterio-, and phytoplankton < 10 µm in size, were monitored daily and analysed using flow cytometry for 19 consecutive days in six mesocosms. Three mesocosms (control) had the same natural water temperature as the lagoon, and the other three were warmed by + 3 °C in relation to the control temperature. The cytometric analyses revealed an unexpected community dominated by picophytoplanktonic cells, including Prochlorococcus-like and Picochlorum-like cells, which had not previously been found in Thau Lagoon. The experimental warming treatment increased the abundances of nanophytoplankton, cyanobacteria, bacteria and viruses during the experiment and triggered earlier blooms of cyanobacteria and picoeukaryotes. Only the abundance of Picochlorum-like cells was significantly reduced under warmer conditions. The growth and grazing rates of phytoplankton and bacterioplankton estimated on days 2 and 8 showed that warming enhanced the growth rates of most phytoplankton groups, while it reduced those of bacteria. Surprisingly, warming decreased grazing on phytoplankton and bacteria at the beginning of the experiment, while during the middle of the experiment it decreased the grazing on prokaryote only but increased it for eukaryotes. These results reveal that warming affected the Thau Lagoon plankton community from viruses to nanophytoplankton in fall, inducing changes in both dynamics and metabolic rates.

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“…Thau Lagoon is another particularly interesting case of Mediterranean coastal lagoon eutrophication. Thau lagoon is an ecosystem located at the Mediterranean French coast, known by supporting traditional shellfish farming activities in France and which has been subject to eutrophication leading to large anoxic events associated with significant mortality of shellfish stocks (Derolez et al 2020). In this context, the North Lagoon of Tunis, a South Mediterranean lagoon, located in the north of Tunisia, provides a good example for the diagnosis and study of eutrophication in Mediterranean coastal ecosystems.…”

Section: Introductionmentioning

confidence: 99%

Machine Learning modeling techniques for forecasting the trophic level in a restored South Mediterranean lagoon using Chlorophyll-α

Hadid

Goyet

Chaar

et al. 2021

Preprint

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An Artificial Neural Network (ANN), a Machine Learning (ML) modeling approach is proposed to predict the ecological state of the North Lagoon of Tunis, a shallow restored Mediterranean coastal ecosystem. A Nonlinear Auto Regressive with exogenous input (NARX) neural network model was fitted to predict Chlorophyll- a (Chl- a ) concentrations in the North Lagoon of Tunis as an eutrophication indicator. The modeling is based on approximately three decades of monitoring water quality data (from January 1989 to April 2018) to train, validate and test the NARX model. The most relevant predictor variables used in this model were those having a high permutation importance ranking with Random Forest (RF) model, which simplified the structure of the network, resulting in a more accurate and efficient procedure. Those predictor variables are secchi depth, and dissolved oxygen. Various model scenarios with different NARX architectures were tested for Chl- a prediction. To verify the model performances, the trained models were applied to field monitoring data. Results indicated that the developed NARX model can predict Chl- a concentrations in the North Lagoon of Tunis with high accuracy (R= 0.79; MSE= 0.31). In addition, results showed that the NARX model generally performed better than multivariate linear regression (MVLR). This approach could provide a quick assessment of Chl- a variations for lagoon management and eco-restoration.

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Two decades of oligotrophication: Evidence for a phytoplankton community shift in the coastal lagoon of Thau (Mediterranean Sea, France)

Cited by 40 publications

References 73 publications

Fifty years of ecological changes: Regime shifts and drivers in a coastal Mediterranean lagoon during oligotrophication

Fifty years of ecological changes: Regime shifts and drivers in a coastal Mediterranean lagoon during oligotrophication

Effects of experimental warming on small phytoplankton, bacteria and viruses in autumn in the Mediterranean coastal Thau Lagoon

Machine Learning modeling techniques for forecasting the trophic level in a restored South Mediterranean lagoon using Chlorophyll-α

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