The quality of ecosystems and effects on organisms; the use of biological indicators

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Canche, Authie, Somme and Seine estuaries

The Canche estuary
The Canche estuary is one of the rivers that flow from the plateau of the southern Boulonnais and Picardy, into the English Channel. It is located in the department of Pas-de-Calais and is bordered by the town of Etaples in north and Touquet in the south. The Canche is a small estuary approximately 10 km in length and 1.5 km in width at its mouth, 7.8 km2 of surface and 6.9 m tidal range with a mean annual average of 11 m3 s-1 freshwater inputs. Forming an alluvial valley, the Canche is a verdant landscape of calm waters, marshes, meadows and small woods. The gentle gradient, averaging 1.5%, gives the river a meandering course. With sandbars and spits, the estuary of the Canche is typical of the estuaries of this region of France. The coastal dunes, marshes and valley are home to 485 different plants and a diverse range of wildlife. In terms of ichthyology, the Canche estuary was mostly used as temporary habitat by fish, as feeding or nursery grounds. Numerous individuals caught in this estuary were juveniles of euryhaline marine fish species (Amara et al., 2007; Selleslagh and Amara, 2008a).
The Authie estuars
Authie estuary is a macrotidal system (maximum tidal range of 8.5 m at its mouth) located in the northern part of France, at the border between the departments of Pas-de-Calais and the Somme and it is localised between Berck sur mer in the north and Fort-Mahon in the south. The mean annual discharge of the Authie estuary is 10 m3 s−1, and the estuary has a 985 km2 catchment area and 12.8 km2 of surface. The Authie, as a small estuary, is approximately 12 km in length and 1.5 km in width. This estuarine system is rapidly filling with silting, but a chief feature is the penetration of a substantial sand fraction originating from the English Channel. Morphologically, the Authie consists of a bay protected by a sand bar (located in subtidal to supratidal domains) at its mouth, which shelters the estuary from storm swells. The principal hydrodynamic feature is the rapid filling of the bay by the tide: during low tide, most of the estuary, except the main channel, is sub-aerially exposed, and during the flood period there is significant resuspension of fine sediment. The Authie estuary is considered to be a relatively “natural estuary”, compared with other local systems, although some polders have been constructed, inducing a seaward salt marsh progression and increased sedimentation (Anthony and Dobroniak, 2000).
The Somme estuary
The Somme estuary, located between Le Crotoy at north and Saint Valéry at the south, is found within the region of Picardie. It is a large megatidal ecosystem of the eastern English Channel (France) with an intertidal area (excluding salt marshes and channels) of 42.5 km2 occupied by seven distinct biosedimentary facies. It is characterized by a rather low fresh water input (35 m3 s-1) and strong hydrodynamic processes. Spring tides reach a height of 9.8 m and the salinity on mud flats rarely drops below 25 psu. The Somme has a 6550 km2 catchment area. It is approximately 14 km in length because of its delimitation the upper estuarine part by the presence of a dam, but extends on approximately 6 km in width at its mouth. The Somme basin is dominated by intensive cereal agriculture, which forms the major part of the catchment area. The main socio-economic activities consist of traditional practices such as hunting, cockle and inshore fishing and harvesting of vegetable products. In the surrounding polders, traditional agriculture is surviving. For the past few decades, tourism has developed on a large scale and has helped reorganize entirely the local economy. In order to manage the environment in a sustainable way, local authorities have installed a management body, called ‘’Syndicat Mixte pour l’Aménagement de la Côte Picarde’’ (SMACOPI). The syndicate claims restoring and rehabilitating estuarine features as well as opening new facilities to tourists in the area. The population density is relatively low (100 inhab / km2), with only three large urban centers. These are settled in the upper part (Saint- Quentin 60,000 inhab), in the middle part (Amiens 160,000 inhab), and along the downstream canalized part of the drainage network (Abbeville 30,000 inhab) (Cabioch and Glaçon, 1975; Amara et al., 2007).

Choice of European flounder (Platichthys flesus, L., 1758) as a biological model

The shallow marine coastal zones of the eastern channel and southern bight of the North Sea provide important nursery habitats for juvenile flatfish (Riou et al. 2001). First of all, young fish utilize estuaries and near-shore marine areas as nursery in order to benefit from the availability of food and perhaps also to gain protection from predators (McLusky and Elliot, 2004). In addition, juveniles in estuarine nursery areas tolerate and overcome some of the occurring environmental constraints (Vasconcelos et al., 2009). Hence, they can settle down in estuaries as their nursery grounds during an important part of their life and can reflect the environmental conditions changing. Finally, juvenile’s fish, as free-living and fast-developing organisms, are also highly susceptible to pollutants in the environment. Investigating, in situ and experimentally, how environmental disturbances affect the quality of fish juveniles is a major importance to understand their consequences on the population renewal of marine species (Rochette et al., 2010).
The European flounder (Platichthys flesus) is a flatfish of European coastal waters from the White Sea in North to the Mediterranean and the Black Sea in South. P. flesus was chosen as a suitable species in situ study for several reasons (Figure 7). Firstly, it widely distributed in marine and brackish habitats throughout Europe, especially, along the French coast of the Eastern English Channel (EEC) in low salinities during the first months following their settlement. Juveniles of this species concentrate in estuaries and are one of the most important components of the demersal fish assemblage in European estuarine waters. Secondly, it is common in both polluted and clean estuaries; and it prefers fine-grained to sandy sediments. As with many other flatfish, flounder migrate to deeper waters (20-60 m) during the winter months to spawn but return to shallow water (2-15 m) in the same estuary during the summer period. Finally, the European Flounder is commonly used in biomarker studies previously and also for environmental monitoring and toxicology studies in France and northern European waters. For example, this species has been adopted by the OSPAR Joint Assessment and Monitoring Programme as the sentinel species for biological effects monitoring in inshore/estuarine waters of the OSPAR maritime area. Therefore, they are more sensitive to the effects of pollution and other types of habitat degradation, since they feed on benthic organisms and live in close association with the bottom sediments, where most of the chemicals introduced into aquatic environments by human activities accumulate. (Sulaiman et al., 1991; Minier et al., 2000; Adams, 2002 ; Marchand et al., 2004; Kirby et al., 2004; Williams et al., 2006; Selleslagh and Amara, 2008a).

READ  Relationships of Environmental Factors and Benthic Macroinvertebrate Assemblages

Measurement of environmental parameters

Fish species are closely related to its environment and reflects both environmental conditions and integral factors (Liasko et al., 2010). As estuaries are important nursery grounds, it has been reported that such environmental influences are most likely to affect juveniles during their estuarine residency (Attrill and Power, 2002). In order to understand this relationship between fish juveniles and environmental factors, some abiotic and biotic variables were integrated in this study.

Physicochemical parameters

Prior the fish sampling, water physicochemical parameters (temperature (°C), salinity, oxygen (mg/l), conductivity (µS/cm) and pH using a Hanna HI 9828 multiprobes; turbidity (NTU) using a waterproof turbidimeter (Eutech instruments, TN-100) and depth (m) using a Garmin Fishfinder 250 sounder) were measured in each station of estuaries.

Table of contents :

Chapter I: General introduction
I.1. Coastal zones and its importance
I.2. Context of the Eastern English Channel
I.3. The quality of ecosystems and effects on organisms; the use of biological indicators
I.4. Fish as bioindicator of aquatic habitats
I.5. Thesis objectives and organisation
Chapter II: Methodology
II.1. In situ approach
II.1.1. Canche, Authie, Somme and Seine estuaries
II.1.2. Choice of European flounder (Platichthys flesus, L., 1758) as a biological model
II.1.3. Sampling strategies
II.1.4. Measurement of environmental parameters
II.1.4.1. Physicochemical parameters
II.1.4.2. Sediment sampling
II.1.4.3. Sediment analysis
II.1.4.3.1. Macrobenthos
II.1.4.3.2. Granulometry
II.1.4.3.3. Organic matter
II.1.5. Feeding analysis
II.2. Experimental approaches
II.2.1. Choice of European sea bass (Dicentrarchus labrax, L., 1758) as a biological model
II.2.2. Microcosm experience on sea bass juveniles (Dicentrarchus labrax, L. 1758) exposed to estuary sediment contamination
II.2.3. Mesocosm experiences on the effects of two toxic algal blooms: Phaeocystis globosa and Pseudo-nitzschia pseudodelicatissima on the physiological performance of sea bass juveniles (Dicentrarchus labrax, L., 1758)
II.2.3.1. Phytoplankton strains and culture conditions
II.2.3.2. Phytoplankton experimental procedure
II.2.3.3. Sampling
II.3. Other analysis of in situ, microcosm and mesocosm experiences
II.3.1. Sediment analysis
II.3.1.2. Metal analysis
II.3.1.3. Polycyclic aromatic hydrocarbons and Polychlorinated biphenyls analysis
II.3.1.4. Metal analysis: a) in fish and b) in fish gills
II.3.2. Biomarkers
II.3.2.1. Standard and samples preparations
II.3.2.2. Biotransformation (detoxification) enzymes
II.3.2.3.Antioxidant enzymes (oxidative stress biomarkers).
II.3.3. Fish mortality and physiological performance indicators
II.3.3.1. Daily mortality
II.3.3.2. Biological analysis
II.3.3.3. Specific growth rate in length and weight
II.3.3.4. Morphological condition index
II.3.3.5. Growth index
II.3.3.6. Nutritional indices
II.3.3.6.1. TAG/ST ratio
II.3.3.6.2. RNA/DNA ratio
II.3.4. Histology
II.3.5. Analysis of two algal blooms: Phaeocystis globosa and Pseudo-nitzschia pseudodelicatissima
II.3.5.1. Colorimetric method analysis for transparent exopolymer particles (TEP)
II.3.5.2. Sampling and determination of Pseudo-nitzschia pseudodelicatissima total abundances
II.4. Statistical analysis
Chapter III: Pollution impact on fish
III.1. Relating biological responses of juvenile flounder to
environmental characteristics and sediment contamination of estuarine nursery areas
III.1.2. Introduction
III.1.3. Materials and Methods
III.1.3.1. Study area and sampling
III.1.3.2. Environmental variables
III.1.3.3. Sediment contaminant analysis
III.1.3.3.1. Metal analysis
III.1.3.3.2. PAHs and PCBs analysis
III.1.3.4. Fish metal analysis
III.1.3.5. Biological analysis
III.1.3.5.1. Growth and condition indices
III.1.3.6. Feeding analysis
III.1.3.7. Statistical analysis
III.1.4. Results
III.1.4.1. Environmental variables
III.1.4.2. Fish biological responses
III.1.5. Discussion
III.2. Effects of estuary sediment contamination on physiology, biochemical biomarkers and immune parameters in juvenile European sea bass (Dicentrarchus labrax, L., 1758)
III.2.1. Introduction
III.2.2. Materials and Methods
III.2.2.1. Sediment collection
III.2.2.2. Fish and experimental set up
III.2.2.3. Sediment analysis
III.2.2.4. Physiological parameters
III.2.2.5. Molecular biomarker analysis
III.2.2.6. Metal analysis in gills
III.2.2.7. Histology
III.2.2.8. Statistical analysis
III.2.3. Results
III.2.3.1. Environmental parameters
III.2.3.2. Physiological parameters
III.2.3.3. Metal concentrations in gills
III.2.3.4. Biomarker responses
III.2.3.5. Immune system responses
III.2.3.6. Correlation between parameters
III.2.4. Discussion
III.2.4.1. Estuarine sediment contamination and metal accumulation in fish gills
III.2.4.2. Physiological indicators
III.2.4.3. Biomarker responses
III.2.4.4. Immune system alterations
III.2.5. Conclusion
Chapter IV: Effects of algal bloom
IV.1. Effects of transparent exopolymer particles (TEP) derived from
Phaeocystis globosa bloom on the physiological performance of
European sea bass juveniles
IV.1.1 Introduction
IV.1.2. Materials and Methods
IV.1.2.1. TEP production from decaying algal cultures and foam
IV.1.2.2. Experimental set up and sampling strategy
IV.1.2.3. Determination of TEP concentrations
IV.1.2.4. Fish mortality and physiological performance
IV.1.2.5. Statistical analysis
IV.1.3. Results
IV.1.3.1. Physico-chemical variables
IV.1.3.2. TEP concentrations
IV.1.3.3. Fish mortality and physiological performance
IV.1.4. Discussion
IV.2. Does Pseudo-nitzschia pseudodelicatissima can be deleterious to the growth and condition of European sea bass juveniles?
IV.2.1 Introduction
IV.2.2. Materials and Methods
IV.2.2.1. Pseudo-nitzschia pseudodelicatissima algal cultures
IV.2.2.2. Experimental set up and sampling strategy
IV.2.2.3. Sampling and determination of Pseudo-nitzschia pseudodelicatissima total abundances
IV.2.2.4. Fish mortality and physiological performance
IV.3.2.5. Statistical analysis
IV.2.3. Results
IV.2.3.1. Physico-chemical variables
IV.2.3.2. Pseudo-nitzschia pseudodelicatissima total abundance
IV.2.3.3. Fish mortality and physiological performance
IV.2.4. Discussion
Chapter V: General Conclusion
V.1. Pollution impact on fish
V.2. Effects of algal bloom
V.3. Perspectives
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