Goal 1

Interactions between contaminants and marine ecosystems

Phase I of the LMI made it possible to obtain a range of data on the levels of chemical and biological contamination and their environmental impacts in different Tunisian coastal ecosystems (Bay-Lagoon of Bizerte, Bay of Tunis, Gulf of Gabès). These achievements will provide the basis for writing a white paper that will present the state of coastal ecosystems and will be very useful for environmental managers. During phase II, the interactions between contaminants and marine ecosystems will be understood in order to respond to five main challenges.

Contaminant interactions and first trophic links

The effect of contaminants on the first links of food webs (planktonic organisms) has been demonstrated in several Mediterranean ecosystems. However, few data exist to date on the link between the bioavailability of contaminants, which strongly depends on their state of coordination complex with natural dissolved organic matter (DOM), and their impact on biota. However, knowledge of the bioavailability of contaminants is essential to assess and predict their impact on the marine environment. The degree of bioavailability of contaminants, as well as the influence of abiotic factors on the latter, will therefore be evaluated during phase II. Some planktonic organisms are bioindicators of pollution and can therefore be considered as tools for biomonitoring and early diagnosis of the state of the environment.

In addition, evaluating the effects and accumulation of contaminants in plankton poses real methodological challenges and requires the support of several disciplines of chemistry and biology. An interest will be given to the smallest fraction of plankton (pico- and ultra-phytoplankton), to understand how these communities interact with contaminants and how they contribute to their bioaccumulation in food webs. This action will be carried out during the MERITE-HIPPOCAMPE 2019 oceanographic campaign (INSU-MISTRALS-AT “Pollution and Contaminants” framework), which concerns the study of chemical contamination at the base of pelagic food webs (plankton) via a trans-Mediterranean approach. North-South, and in which several LMI partners are involved.

Dispersion/transport of contaminants

It is important to determine the fate of contaminants in coastal ecosystems and particularly in chemical pollution hotspots (such as the Gulf of Gabès, the Bizerte lagoon, etc.). This requires the study of the dispersion and transport of contaminants according to different physical forcing. A description of the major features of coastal dynamics in the Gulf of Gabes based on Lagrangian (drift buoys) and Eulerian (ADCP) data and a study of the distribution of plankton communities forced by hydrodynamics and the degree of pollution have been already initiated as part of the MERITE Gabès 2017 campaign (bringing together INSTM, FSB, FSS, CBS and MIO). These data will make it possible to feed/validate the models of dispersion and transport of contaminants from particles and plankton coupled to a model of coastal circulation and to better appreciate the relationships between contamination and planktonic habitats.

Transfer of contaminants in food webs

The impacts of contaminants on marine populations and communities have been well described (phase I), while little data exists on their effects at the functional scale (i.e. processes and activities). This point will therefore be better developed during phase II. The results will be of great importance since the structural and functional changes induced by the contaminants will be integrated into trophic transfer models (objective 3), which will make it possible to highlight the main trophic transfer pathways in environments strongly impacted by Pollution.

This action is part of the national GAMMA project (2016-2019), coordinated by the INSTM, and carried out as part of a collaboration between the INSTM and the FSB. Similarly, HSM and INSTM have developed a methodology for studying sediment cores in pre estuarine areas, which makes it possible to trace the history of solid inputs over the past decades, and the possibility of quantifying the associated contaminants. This methodology will be developed on other sites in coordination with the LMI partners, and the content of the cores could be the subject of in-depth studies, in particular on the origin of the clays, on the content of contaminants.

Atmosphere-marine ecosystem interactions

Atmospheric deposits (aerosols or Saharan dust) in marine ecosystems are important sources of nitrogen and phosphorus, also of contaminants such as ETMs and PAHs. These inputs are very frequent pulsed phenomena whose impact on marine ecosystems in the Mediterranean is well established but not yet fully quantified. The study of the impact of atmospheric inputs on plankton communities (bacterio-, phyto- and microzoo- plankton) has already been initiated during phase I within the framework of two transverse actions (AéroBiz and AéroSfax) carried out in the Lagoon -Bay of Bizerte and the Gulf of Gabès, which border the North African coast widely considered to be the greatest source of dust for the Mediterranean.

Moreover, this dust has a wide range and affects the northern coasts of the Mediterranean. The importance of atmospheric inputs will be assessed on a trans-Mediterranean scale during the MERITE-HIPPOCAMPE 2019 campaign (CHARMEX – MERMEX transversally in the “Pollution and Contaminants” TA of MISTRALS). In addition, systems for collecting atmospheric deposits will be installed at various stations in the Gulf of Gabes to assess the temporal variability of these inputs.

The response of plankton to strong and sporadic atmospheric deposition events has often been studied under controlled experimental conditions as close as possible to natural conditions such as mesocosms, but rarely in-situ. In-situ and high-frequency (spatial and temporal) observation at the individual cell scale using high-frequency flow cytometry will make it possible to study the dynamics of the impact of these phenomena on phytoplankton, to quantify this impact in terms of production, biomass and selective response to such environmental changes.

Emerging contaminants

The progress of our knowledge on emerging contaminants (microplastics, pharmaceutical products, etc.). The Claim project (H2020-BG7) in which two LMI partners are involved (MIO and INSTM) is excellent support for moving forward in this area of ​​research. The study of the spatial distribution and characterization of microplastics in surface water and sediment has already begun in the Gulf of Gabes as part of the MERITE 2017 campaign. Developing analysis methods (chromatographic, optical) of these emerging contaminants and their distribution (dissolved-solid) will also be a challenge for phase II. HSM also has skills in the analysis of drug residues, which will be combined with those of the LMI partners.