1

Le benthos dans le canal de rejet thermique de la centrale côtière du

Havre (France).

Benthos in the thermal discharge canal of the coastal power station of

Le Havre (France).

Auteurs: François Ghillebaert1, Isabelle Ghillebaert

1, Chloé Dancie

2 and Gérard Breton

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Adresses:

1 Ecotox, 11 rue Principale, Fr-62380 Affringues.

2 Cellule de Suivi du Littoral Normand, 53 rue de Prony, Fr-76600 Le Havre.

3 Association Port Vivant, 6 rue des Réservoirs, Fr-76600 Le Havre.

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Résumé La centrale côtière du Havre (France), située en Manche orientale, est composée de 3 tranches

de production électrique au charbon. Initialement, le traitement anti-salissures des circuits

d’eau de réfrigération été réalisé par une électrochloration en continu. En 1996, la chloration a

été substituée sur la tranche 1 par une injection en discontinue du produit Mexel® 432/0. Ce

traitement a été alors étendu aux unités 2 et 4 en 1997 et 2006 respectivement. L'impact

potentiel de ce nouveau traitement sur les organismes benthiques a été évalué par un index

biotique marin (logiciel d'AMBI) réalisé sur des prélèvements d’échantillons de sédiment

effectués en 2000, 2006, 2009 et 2012 dans le canal de rejet de la centrale. Lors de chaque

campagne d'échantillonnage, il est montré que les populations benthiques sont fortement

perturbées au point de rejet de la centrale. Cependant, la biodiversité est récupérée après

quelques centaines mètres, et la biodiversité ne se détériore pas au cours de cette période. La

perturbation de la biodiversité endobenthique n'a pas pu être attribuée directement à un

facteur spécifique comme le traitement anti-salissure, le rejet thermique, la vitesse de l'eau ou

les caractéristiques sédimentologiques.

The coastal power station of Le Havre (France), located in the Eastern English Channel,

operates 3 coal-fired units. Initially, the anti-fouling treatment of the cooling systems was

continuous electrochlorination. In 1996, the chlorination was replaced on Unit 1 by a

discontinuous injection of Mexel® 432/0 product. This treatment was then extended to the

units 2 and 4 in 1997 and 2006 respectively. The potential impact of this new treatment on the

benthic organisms was evaluated in the discharge canal of the power plant using the Marine

Biotic Index (AMBI software) on samples collected in 2000, 2006, 2009 and 2012. Each

sampling campaign demonstrated that the benthic organisms were highly affected at the

discharge point. However, the biodiversity was recovered a few hundred meters away, and no

deterioration of the biodiversity was observed through this period. The disturbance of the

endobenthic biodiversity could not be directly attributed to a specific factor like anti-fouling

treatment, thermal discharge, water velocity or sedimentology characteristics.

Mots clés:

Endobenthos, AMBI, Mexel, Anti-fouling, biodiversity

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Benthos in the discharge canal of the power station of Le Havre

1. Introduction Coastal electric power plants use sea water for cooling to complete the steam cycle. The

cooling water requirement for fossil fuelled power plants is about 30 m3s

-1/1000 MWe with a

temperature rise of 10 °C (Khalanski & Gras, 1996). This water is pumped and discharged

into the sea through an open cooling water system (CWS) without water preconditioning.

That is why, the sessile aquatic organisms at a planktonic stage (e.g. mussels, barnacles,

hydroids …) or bacteria can colonize the CWS, reducing the thermal efficiency and

increasing the risk of shut down linked to clogging the heat exchangers by the sudden release

of macrofouling into the water flow.

To limit the biofouling development, different chemicals or mechanical strategies have been

used. The most often-used is the water chlorination by direct injection of chlorine, stored at

the power plant under different forms (sodium hypochlorite solution, chlorine gas) or

produced in situ by seawater electrolysis (Jenner et al., 1998).

The coal-fired power station of Le Havre (Eastern English Channel, France) is located in the

tidal docks of the harbour. In 2012, this power plant has three units in service (Units 1, 2 and

4) using sea water pumped in the harbour (Table I). Unit 1 has a capacity of 250 MWe and a

cooling water flow rate of 9 m3s

-1. Each of the units 2 and 4 has a capacity of 600 MWe and a

water flow rate of 22 m3s

-1. At full load, the cooling water discharge of the power plant is thus

approximately 53 m3s

-1, with a temperature increase of approximately 9 °C. Initially, the anti-

fouling treatment for the 3 units was continuous electrochlorination at a concentration of

1 mgL-1

(HOCl) with a total concentration of free oxidant in the discharge ≤ 0.1 mgL-1

(Jenner et al., 1998). In units 1 and 2, this treatment was supplemented by a ferrous sulphate

treatment for corrosion inhibition protection of the tubes. In 1996, the power plant replaced

the chlorination and ferrous sulphate treatment of the unit 1 by the Mexel® 432/0 product.

Then, this treatment was extended to the units 2 and 4 respectively in 1997 and 2006. In 2008,

the Mexel® 432/0 product was reformulated to be in accordance with the European Biocidal

Product Directive (European Parliament Council, 1998). This new formulation is sold under

the name Mexel® 432/336/0. The Mexel

® 432 products are aqueous emulsions of aliphatic

amines classified as non-oxidizing biocide.

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At the power plant of Le Havre, several protocols of injection of the Mexel®432 products

were used. However, the mass of product daily injected was equivalent to an injection of

Mexel® 432/0 around 5 to 6 mgL

-1 during 30 to 45 minutes. Under these conditions, the

residual concentration of Mexel®

432 product at the discharge of the power station ranged

between 0.23 and 30 mgL-1

according to the treated unit and of the activity of the others units.

In the discharge canal, the Mexel®

432 concentration decreased quickly first due to water

dilution by the others units and water from the plume dilution, adsorption of alkylamines on

suspended solids, and by subsequent biodegradation. For these two lasts mechanisms, using a

primary degradation test in natural sea water filtered through a 1.0 μm at 20±1 °C, the

decrease of the Mexel®

432/0 concentration was more than 50 % after 2 days and 90 % after

15 days at an initial concentration of approximately 12 mgL-1

(López-Galindo et al., 2010).

For the Mexel®

432/336/0 product (Mexel, 2010), to sea water organisms in synthetic media,

the EC50 72 hrs to the algae Phaeodactylum tricornutum is 0.25 mgL-1

, the EC50 48 hrs to the

crustacean Arcatia tonsa is 0.96 mgL-1

and to the fish Scophthalmus maximus the LC50 96 hrs

is 3.70 mgL-1

. For the Mexel® 432/0 product, in synthetic sea water, López-Galindo et al.

(2010) obtained to the microalgae Isochrysis galbana and Dunaliella salina an EC50 96 hrs of

4.55±0.11 mgL-1

and 7.21±0.1 mgL-1

and on the invertebrate Brachionus plicatilis using

growth inhibition and death tests a LC50 24 hrs of 3.62±0.37 mgL-1

. According to these

authors, during the treatment the instantaneous Mexel® 432 concentrations at the discharge of

the power plant were higher or around the L(E)C50.

That is why, the potential impact of the anti-fouling treatment on the aquatic organisms in the

discharge canal of the power plant was evaluated after the implementation of the Mexel 432

treatment at the power plant and before and after the modification of the formulation of the

Mexel® 432 product. Benthic organisms are good indicators since they have limited ability to

escape (Bamber & Spencer, 1984). To this end, benthos evaluations were made in 2000, 2006,

2009 and 2012 at different sampling sites more or less distant from the discharge point of the

cooling water.

2. Material and methods

2.1. Sampling sites and methods

The harbour of Le Havre (42° 29' N; 0° 07' E) is located at the Seine lower estuary, in the

eastern English Channel (Figure 1). The power plant is on the tidal dock directly connected to

the open sea. Tidal range varies from 2.2 meters (neap tide) to 8 meters (spring tide). The

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cooling water used for the power plant is pumped from, and discharged to, the same dock. The

discharge canal is built of a concrete wall at its left and an old sheet piling bulkhead of steel at its

right side, in which a lot of leaks allow transfer a part of the discharge water. Four sampling

stations (2, 3, 4 and 5) were selected along the discharge canal. Three stations have been selected

as reference sites (1a, 1b and 6). The stations 1a and 1b are close to the discharge canal. The

station 1c is between the reference and the discharge canal can be potentially affected by the

discharged water due to the poor conditions of the sheet piling. The station 6 is located in front of

the inlet of the cooling system and the station 7 is close to the discharge of a sewage station. All

of these reference sites were not studied each time.

In 2000, 2006, 2009 and 2012, sediment samples were collected from a boat, using a Smith-

McIntyre grab sampling of 0.10 square meter and approximately 20 cm depth. The samples

were conditioned directly on board. For benthic organism evaluation, the sediments were

washed with sea water under pressure on a 1-mm mesh-size sieve. Then, retained materials

constituting the biological samples were fixed with 10 % salted formaldehyde and coloured

during several days with Phloxin B. The animals were then identified and counted.

Taxonomic treatment was as up-to-date as possible, keeping therefore in mind that

identifications were made by general taxonomists.

The sediment samples were processed during the winter the 20th

of December 2000, and during

the spring the 14th June 2006, the 29

th of May 2009 and 11

th of June 2012. Different teams were

involved in the study, inducing differences of sampling site and number of samples processed by

sampling site. The number of sediments samples processed at each station ranged between 0 and

6 according to the date of the campaign (Table II). In 2000, 2006 and 2009, when multiple

samples were processed at one station, they were gathered before benthic organism

identifications.

In 2012, the determination of organisms was completed by measurements of the total biomass

by species or taxon. The biomass was obtained by difference between the dry weight and the

ash weight of individuals gathered either by species or genus or family. The dry weight was

measured after 48 hours at 60°C; the weight of mineral ashes, was obtained after calcination

of the dry matter for 2 hours at 550 °C.

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2.2. Assessment of the benthic ecological quality

The benthic ecological quality at the various sampling stations was done by Marine Biotic

Index (AMBI) and multivariate AMBI (M-AMBI) using the AMBI software (Borja et al.,

2000). AMBI is derived from the proportions of individual abundance in five ecological

groups, which are related to the degree of sensitivity/tolerance to an environmental stress

gradient (Borja et al., 2000). It is calculated according to the following formula:

AMBI = ((0 x % GI) + (1.5 x % GII) + (3 x % GIII) + (4.5 x % GIV) + (6 x % GV))/100

With GI: Group I: species very sensitive; GII, Group II: species indifferent; GIII, Group III:

species tolerant; GIV, Group IV: second-order opportunistic species; GV, Group V: first-

order opportunistic species

The production of a continuous Biotic Coefficient makes it more suitable for statistical

analysis.

The multivariate AMBI (M-AMBI) is a factor analysis on Shannon’s diversity, richness and

AMBI (Muxika et al., 2007).

2.3 Statistical analysis

Statistical analysis was processed using the xlstat software (AddinsoftTM

version 2012.6.04).

The results were evaluated for normality and homogeneity of variances. In the cases of the

assumptions of normality and homogeneity of variances were not met, homogenisations of

variances were processed using the Box-cox transformation Then, ANOVA, Dunnett’s and

Tukey procedure were used to evaluate the data.

In 2000, 2006 and 2009, when multiple samples were processed per station, they were

gathered before benthic organism identifications. In 2012, the samples were studied

individually. That is why, statistical analysis on density and richness were performed

separately on the samples of 2012 to study the differences between stations. Then, all the

samples (sampling station x year) were studied simultaneously to observe the site and year

influences.

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3. Results Whatever the station, the sedimentary bottom was composed of soft to compact reduced mud

covered with a cream of mud. At the discharge point, the substrate was composed of little

mud with a lot of shell debris mainly of mussel shells and walls of barnacles, this being the

result of the winnowing of the smallest particles by the current. At the end of the discharge

canal, the size of the particles increased slightly to obtain a sandy mud.

3.1. Benthos

In this study, 152 taxa were observed (Table III); 51 % were Annelida, 19 % Arthropoda and

18 % Mollusca. However, based on the taxonomic identification limit and using the list of the

AMBI software for the attribution of ecological group, only 134 taxa were used.

Richness

The lowest richness of 6 taxa was measured in 2000 at the sampling point 1c and the highest

of 43 taxa was observed in 2012 at the sampling point 6 (Figure 2). A median number of 16

was determined for all the stations.

The richness ranged from 6 to 13, 9 and 17, 13 and 28 and between 28 and 43 taxa

respectively in 2000, 2006, 2009 and 2012. Over this period, and for the station studied each

time, the mean richness per station was for the station 1a, 3, 4, and 5 respectively 20.3, 16, 21,

and 22.3 taxa and no statistically significant differences could be observed. In 2012, the

richness for the station 1a, 2, 3, 4, 5 and 6 ranged from 19 to 29, 9 – 25, 13 – 18, 19 – 23, 21 –

32 and from 16 to 34 taxa. According to the Tukey’s test the richness in 2000 was equal to

this observed in 2006, significantly lower than the richness measured in 2009 and in 2012

(Figure 2). When the richness was low, no statistical difference was observed between

stations. Using the richness of stations 1a, 3, 4, 5 of years 2009 and 2012, the increase of the

richness across the discharge canal seems significant with a significant higher richness value

at the end of the canal (Station 5) compared to station 3.

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Density

Whatever the sample (station x year of sampling), the density of organisms ranged from 637

to 24 113 individuals.m-2

with a median number of 5 613 individuals.m-2

(Figure 3). The

lowest densities were observed in 2000 at the reference sampling point (1a) and at the inlet of

the power plant (sampling point 6). The highest density was measured in 2009 in the

reference sampling point 1b. The median density was 1899, 6070, 7157 and 3333 respectively

in 2000, 2006, 2009 and 2012.

The variability of the density between the different control stations 1a, 1b and 6 ranged from

637 to 2610 individuals.m-2

in 2000, 2870 and 7350 in 2006, 2547 and 24113 in 2009 and

2357 and 4310 individuals.m-2

in 2012. High variability was also observed, between sediment

samples processed the same year at the same sampling point. For example, for the 3 samples

processed at the reference station 1a in 2012, the density ranged from 1050 to 3220

individuals.m-2

, and for the sample reference 6, the density ranged from 1230 to 8170

individuals.m-2

. Using all the data, no statistically significant differences could be observed

between years or sampling stations. In 2006, 2009 and 2012, a significant decrease of the

density was observed at the station 3 compared to the station 5. In 2012, at the station 5, the

density of organisms.m-2

was significantly higher than in station 1a, 2 and 3. The densities in

stations 4 and 6 were not significantly different from the others.

Biomass

In 2012, the total biomass of the stations ranged from 2.27 to 68.48 g.m-2

(Table IV). The

stations 1a, 2, and 3 were dominated by epibenthic species (Table IV). More than 80 % of the

total biomass was represented by Nassarius reticulatus, Mytilus edulis and Carcinus maenas.

The station 4 was dominated by epibenthic species notably Crepidula fornicata and Mytilus

edulis but biomass of endobenthic species was equally significant, notably Cirriformia

tentaculata (25 % of the total biomass). The biomass of station 5 was represented by

epibenthic (Anthozoa, 36 %) and endobenthic species as Abra alba (6 %), Acanthocardia

echinata (21%) and Nucula nitidosa (14 %). Then, the biomass of station 6 was dominated by

endobenthic species as Euchone rosea (38%), Nephtys hombergii (19%) and Abra alba

(15%).

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Taxonomic composition

Polychaeta were present at every station whatever the year of sampling (Table III). This taxon

cumulated between 11 and 99 % of the number of total individuals.m-2

with a median number

of 77 %. Notably, Cirriformia tentaculata was observed on 22 sampling points (stations and

year) on the 25 processed with a median number of 1615 individuals.m-². This species was not

observed in 2000 in the stations 5 and 6 and in 2006 in the station 1b. Then, and to a lesser

extent, Lagis koreni was observed in 14 stations with a median number of 15 individuals.m-2

and Capitella capitata in 13 stations with a median number of 60 individuals.m-2

. The taxa

Bivalvia was present in 24 sampling out of the 25 processed. This taxa cumulated between 0

and 88 per cent of the number of total individuals.m-2

with a median number of 9 %.

However, it was not observed only in 2000 at the sampling station 4. This taxa is mainly

represented by Abra alba, Corbula gibba, Nucula turgida, and in a lesser extent Mytilus

edulis. Then, Malacostreaca, Anthozoa and Gastropoda were observed respectively in 19, 18

and 18 stations of the 25 sampling but they represented less than 1 per cent of the number of

total individuals.m-2

.

3.2. Ecological indicator

Using the data of all the stations and years, the ecological groups I, II, III, IV and V represent

respectively 23.9, 32.8, 23.9, 14.2 and 5.2 % of the observed species. However, the same

ecological groups represent 15.2, 9.2, 14.1, 47.9 and 13.1 % of the total number of individuals

observed (Table V).

The most often observed species Cirriformia tentaculata, Lagis koreni, Capitella capitata,

Abra alba, Corbula gibba, Nucula turgida and Mytilus edulis belong respectively to the

ecological groups IV, IV, V, III, IV, I and III.

Using the AMBI index software (Figure 4), the sampling stations can be classified from

undisturbed (2000 station 3; 2006 station 1b) to heavily disturbed (2000, station 7; 2012

stations 1a and 3), with most of them as slightly to moderately disturbed.

The sampling stations used as references were classified as undisturbed to heavily disturbed

with a mean of moderately disturbed. In the discharge canal, independently of the year, the

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stations were classified as heavily disturbed to slightly disturbed. The end of the thermal

discharge canal referenced station 5 was classified as slightly disturbed whatever the year.

The station 1c, located between the references points and the discharge canal was classified as

moderately disturbed. The inlet of the power plant was classified between slightly and

moderately disturbed and the discharge of the sewage plant was classified as heavily

disturbed.

4. DISCUSSION

In this study 152 taxa have been observed. This represents about 43% of the taxa observed

between 1992 and 2005 in the Le Havre harbour (Breton, 2005).

According to the hydrodynamism and the observed species, the harbour of Le Havre can be

considered as a paralic dock sensu Guelorget and Perthuisot (1983; 1984) and Guelorget (1985).

For example, in this study species like Ficopomatus enigmaticus and Nereis diversicolor have

been quoted. But others paralic species were observed in other studies processed in the Le Havre

harbour, for instance Chaetomorpha linum, Ulva intestinalis, Ulva lactuca, Cerastoderma

glaucum, Rhithropanopeus harrissii, Balanus amphitrite and Microdeutopus gryllotalpa (Breton,

2005). Due to the sampling method, it is not surprising that algae are not recorded.

Some foreign species, like Ficopomatus enigmaticus, Crepidula fornicata and Molgula

manhattensis settled a long time ago in the European waters and live in the harbour. New

migrants have been recorded notably the invasive species Hydroides ezoensis Okuda settled in

the coastal waters of Western Europa between 1980 and 1990 (Breton, 2005).

The richness of the different stations ranges from 6 to 43 taxa. The richness variation is high

between years of sampling and for a same sampling point between samples processed. This

variation can be linked to the used methodology and the period of sampling. In 2000, only one

sediment sample was processed per station while 6 samples were processed per station in

2006 and 3 in 2009 and 2012. As the samples are pooled before taxonomic identifications in

2006 and 2009, only the samples processed in 2012 are able to demonstrate the spatial

variability of diversity between samples processed at the same station. During this last year,

the richness for the station 1a, 2, 3, 4, 5 and 6 ranged from 19 to 29, 9 – 25, 13 – 18, 19 – 23,

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21 – 32 and from 16 to 34 taxa. Moreover, the richness ranged from 6 to 13, 9 to 17, 13 to 28

and from 28 to 43 taxa respectively in 2000, 2006, 2009 and 2012.

There is a significant increase of the endobenthic biodiversity from 2006 to 2012, with a

doubling of the number of taxa from 2009 to 2012. The results do not reflect necessary a

better quality of the sediment. This apparent increase from 2006 to 2012 mainly depends on

two methodological biases:

- the season of the sampling period or the date in the year of the spring settlement of the

endobenthic biota. The sediments samples were processed the 20th

of December 2000, and

during the spring the 14th

June 2006, the 29th

of May 2009 and 11th

of June 2012. Decrease of

number of macrofaunal species during the winter season was previously described (Bamber &

Spencer, 1984). According to the data set, it can be assumed that the biodiversity increase was

linked more to the normal spring recruitment with inter year variations than to a modification

of the environmental medium

- and possibly the know-how of the staff of taxonomists who identified taxa in 2012, whose

“performances” especially with regard to Polycheta, are high-rated.

A point of comparison is given by the (unpublished) results of the association Port Vivant,

dealing with the global epibenthic biodiversity in the port of Le Havre. The figure of the

specific richness increases slowly and regularly between 2005 (Breton, 2005) and 2012, along

with the progress of their observations. No peculiar acceleration was reported from 2009 to

2012.

Simultaneously, the density of organisms ranged from 637 to 24 113 individuals.m-2

with a

median number of 5 613 individuals.m-2

. Whatever the station, there was more endobenthic

species than epibenthic species. Contrasting with the richness data, median density displays

no statistical difference between the years, with 2610, 6070, 7157 and 3333 individuals.m-2

respectively in 2000, 2006, 2009 and 2012. The density of organisms normally shows a

seasonal cycle (Bamber & Spencer, 1984), the absence of significant difference can then be

linked mostly to the absence of sample repetitions per station and to the high difference

observed between stations during the same year. For example the density was from 637 to

8720 individuals.m-2

in 2000, 2870 and 21750 in 2006, 1963 and 24113 in 2009 and 1990 and

7883 individuals.m-2

in 2012. Even for very near stations like 1a, 1b and 1c, it ranged from

637 to 2610 individuals.m-2

in 2000, 2870 to 7350 in 2006, 2547 to 24113 in 2009 and

2357 individuals.m-2

in 2012. However, this high variability was also observed, between

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sediment samples processed the same year at the same sampling point. For example, for the

3 samples processed at the reference station 1a in 2012, the density ranged from 1050 to

3220 individuals.m-2

, and for the sample reference station 6, the density ranged from 1230 to

8170 individuals.m-2

. That is why, using all the data, no statistically significant differences

can be observed between sampling stations over the total period of the study.

Using the data of all the stations and years, the ecological groups I, II, III, IV and V represent

respectively 15.2, 9.2, 14.1, 47.9 and 13.1 % of the total number of individuals. The

Polychaeta were present at each station whatever the year of sampling and represent from

11 to 99% of the number of individuals observed. Notably, Cirriformia tentaculata,

Pectinaria (Lagis) koreni and Capitella capitata are opportunistic species of second and first

order which belong to ecological groups IV or V adapted to reduced sediments (Grall &

Glémarec, 2003). The bivalvia was the second most often observed taxa. This taxon

cumulated from 0 to 88 % of the total number of individuals.m-2

. It was mainly represented by

Abra alba, Corbula gibba, Nucula turgida, and in a lesser extent by Mytilus edulis. These

species belong respectively to ecological groups III, IV, I and III. The group I is composed of

species sensitive to organic enrichment, while group III accommodates species tolerant to

excess of organic matter enrichment. In agreement with the conclusions of Pruvot et al.

(2000) about the eastern port of Dunkerque (France) and Breton et al. (2005), the Corbula

gibba facies of the Abra alba and Pectinaria (Lagis) koreni communities characterizes a

biocoenosis of the organic-rich, fine sediments in confined harbour environments. That is

why, according to AMBI index software, the different stations in the harbour of Le Havre can

be classified from undisturbed (2000 station 3 ; 2006 station 1b) to heavily disturbed (2000,

station 7 ; 2013 stations 1a and 3), with most of them as slightly to moderately disturbed. The

discharge of the sewage plant (station 7) was classified as heavily disturbed. The enrichment

of the sediment by organic matter of this last station was certainly due to the nearby effluent

of the sewage plant of the city of Le Havre (Breton et al., 2005).

The sampling stations used as references are classified by the Marine Biotoc Index as

undisturbed to heavily disturbed with a mean of moderately disturbed. This relatively low

ecological quality must be put in relation with the fact that the harbour is a paralic medium.

In the thermal discharge canal, independently of the year, the stations were classified as

heavily disturbed to slightly disturbed. The end of the thermal discharge canal referenced

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station 5 was classified as slightly disturbed whatever the year. The inlet of the power plant

was classified between slightly and moderately disturbed.

This gradation between the outlet of the power plant and the end of the discharge canal was

not statistically significantly different as for the richness, due to the high variability of the

richness over this period and between samples processed at the same location. However, when

the data of 2009 and 2012 are analysed simultaneously a significant increase was observed

between the discharge point of the power plant and the end of the thermal discharge canal

(600 m far away). At this last point the biodiversity was close to the reference points. Similar

results were obtained in 2000 at the same location by scuba-diving observations (Breton,

2000; Breton & Vincent, 2002). According to these authors, the number epibenthic taxa was

respectively 5, 13, 24 and 32 around the stations 2, 3, 4 and 5. At the same time, in 2006,

2009 and 2012, an increase of the density was observed at the station 5 compared to the

station 3. In 2012, due to separate treatment of the 3 sediment samples processed per station,

it was observed that the density of organisms.m-² was significantly higher in the station 5 than

in station 1a, 2 and 3. The density in stations 4 and 6 was non-significantly different to the

others.

In the thermal discharge canal, the reduction of the disturbance of the environment between

the outlet of the power plant and the end of the canal can be linked to different factors like the

decrease of water velocity, the heat discharge or the discharge of anti-fouling product like

chlorine (Khalanski, 1976), Mexel®432 products (López-Galindo et al., 2010) or dredging

frequency of the end of the canal (McCauley et al., 1977).

However, as all the factors react simultaneously, it is difficult to estimate the impact of each

parameter. For example, according to Lardicci et al. (1999) the biological environmental

impact of heated effluents may vary greatly as a function of the quantity of heat discharged

and of the climatic, hydrological and biological features of environment. Then, even if

according to different authors, the thermal impact of power plant in sea water is low on

primary production up to 24°C for the water of Dunkerque (English channel, Khalanski,

1976) or on benthic communities (western Mediterranean, Lardicci et al., 1999), in different

cases this factor affects directly benthics and fish communities (Chou et al., 2004; Teixeira et

al., 2009, Atlantic Ocean on Brazil coast). In the same way, as indicated by Abelson and

Denny (1997) or observed by Pawlik and Butman (1993), the water velocity could greatly

affect the settlement of benthic organisms. Potentially, this impact can be linked directly to

the mechanical aspect of the velocity but indirectly by the impact on the sedimentology

observed in the canal and so the associated endobenthic fauna. The discharge point of the

14

power plant is directly affected by the water velocity. At this point the substratum is

composed by shell debris included in mud sediment composed by medium silt. With the

increasing of the distance, the shell debris content decreases and at the station 5 the sediment

can be classified as very fine sandy medium silt. Moreover, at the discharge point, and up to

the station 4, the canal is never dredged due to low sedimentology and difficulties of access.

At the opposite the bottom of the station 5 is frequently dredged. This modification of the

hard bottom seems to impact directly the species spectrum. In 2012, the study of the biomass

demonstrated a relation between the sampling station location and the contribution of the

epibenthic or endobenthic species. At the beginning of the discharge canal, the biomass of

stations 2 and 3 was dominated by epibenthic species. More than 80 % of the total biomass

was represented by Nassarius reticulatus, Mytilus edulis and Carcinus maenas. The station 4

was dominated by epibenthic species notably Crepidula fornicata and Mytilus edulis but

biomass of endobenthic species was equally significantly noticed notably with Cirriformia

tentaculata (25 % of the total biomass). The end of the thermal discharge canal (station 5) was

represented by epibenthic (Anthozoa, 36 %) and endobenthic species as Abra alba (6 %),

Acanthocardia echinata (21%) and Nucula nitidosa (14 %). At the inlet of the power station,

the biomass of station 6 was dominated by endobenthic species as Euchone rosea (38%),

Nephtys hombergii (19%) and Abra alba (15%). However, the biomass measurement was

performed only in 2012, and so no clear relation between epibenthic - endobenthic biomass

and sampling location can be pointed out.

That is why, even if López-Galindo et al. (2010) indicates that anti-fouling treatment using

chlorine or Mexel®432 product can potentially impact the environment, our observations

seem to demonstrate the absence of specific impact of the anti-fouling treatment. Notably, no

drastic decrease of the biological sediment quality was observed when the Mexel®

432/0 was

implemented in one new unit instead of the chlorination in 2006 or when this product was

replaced by the Mexel® 432/336/0 in 2008.

Then, according to this data set, the environmental impact of the discharge water of the power

plant of Le Havre including several factors as water velocity, thermal discharge, antifouling

product seems to be limited to few hundred meters from the discharge to the end of the canal

(site 5 of this study), confirming the observations performed on epibenthic species performed

by scuba-diving (Breton, 2000; Breton & Vincent, 2002).

15

5. CONCLUSION

This study permits generation of the beginning of a temporal biodiversity data set at the

discharge of the power plant of Le Havre. Over a 12 year period no significant trend of

modification of the biologic community could be observed indicating the absence of a specific

effect of the antifouling treatment processed at the power plant of Le Havre. This data set

demonstrated the importance to generate at the discharge of the power plant benthic studies

series over a long time period to erase the variations linked to methodology, or to local or

seasonal conditions in front of long term variations. To minimize the variability of the data it

seems important to perform the samples during the same season, at the same sampling points

and at least in triplicate. In order to complete the data set, it would be interesting to evaluate

the epifaunal specific richness during the same season and at the same sampling points.

ACKNOWLEDGEMENTS:

The authors would like to thank the Mexel Industries SAS for financial support. We would

like to thank equally the team of the TRASOM (Le Havre) for the nautical support, Grand

Port Maritime du Havre for the facilities, the authorizations, Port Vivant and its President

Denis Corthésy for the material help and Mr Rick Kreuser for the English reviewing. Finally,

we thank Mr Michel Khalanski for its critical review of the document and the useful

discussions.

REFERENCES

Abelson A. & Denny M., 1997. Settlement of Marine Organisms in Flow. Annu. Rev. Ecol.

Sys., 28: 317-339.

Bamber R.N. & Spencer J.F., 1984. The benthos of a coastal power station thermal discharge

canal. J. mar. biol. Ass. U.K., 64(3): 603-623.

Borja A., Franco J. & Pérez V., 2000. A Marine Biotic Index to Establish the Ecological

Quality of Soft-Bottom Benthos Within European Estuarine and Coastal Environments. Mar.

Pollut. Bull., 40(12): 1100-1114.

Breton G., 2000. Etude du benthos de sept sites du port du Havre (Seine-Maritime) : quai

Joannès-couvert-est, quai Mazeline, Môle central et quai de l'Atlantique. Muséum d'histoire

naturelle - Ville du Havre; annexes, 2 pl. coul.: 9.

Breton G., 2005. Le port du havre (Manche orientale, France) et ses peuplements : Un

exemple de domaine paralique en climat tempéré. Bull. Soc. zool. Fr., 130(4): 382–423.

16

Breton G. & Vincent T., 2002. La plongée subaquatique permet-elle d'évaluer de manière

fiable la biodiversité de l'épibenthos dans un port ? Bull. Soc. zool. Fr., 127(2): 83-94.

Breton G., Vincent T., Painblanc A. & Duchemin A., 2005. L’endofaune des bassins du port

du Havre (Manche Orientale). Bull. Soc. géol. Normandie et Amis Muséum du Havre, 92(1):

5-18.

Chou Y.L., Chen C.T.A. & Liu L.L., 2004. Effect of nuclear power plant thermal effluent on

marine sessile invertebrate communities in southern Taiwan. J. Mar. Sci. Technol., 12(5):

448-452.

European Parliament Council, 1998. Directive 98/8/EC of the European Parliament and of

the Council of 16 February 1998 concerning the placing of biocidal products on the market.

Official Journal of the European Communities: 63.

Grall J. & Glémarec M., 2003. Chapitre III: L’indice d’évaluation de l’endofaune côtière

I2EC. In Alzieu C. (coord.) : Bioévaluation de la qualité environnementale des sédiments

portuaires et des zones d’immersion. IFREMER ed.: 51-86.

Guelorget O., 1985. Entre mer et continent : contribution à l'étude du domaine paralique.

Université des Sciences et Techniques du Languedoc, Monpellier.725 pp.

Guelorget O. & Perthuisot J.-P., 1983. Le domaine paralique, expressions géologiques,

biologiques et économiques du confinement. Presses de l’École Normale Supérieure. Travaux

du Laboratoire de Géologie, ENS: 136.

Guelorget O. & Perthuisot J.-P., 1984. Indicateurs biologiques et diagnose écologique dans le

domaine paralique. B. Ecol., 15(1): 67-76.

Jenner H.A., Whitehouse J.W., Taylor C.J.L. & Khalanski M., 1998. Cooling water

management in European power stations Biology and control of fouling. Hydroécol. Appl.,

10(1-2): 1-225.

Khalanski M., 1976. Influence du fonctionnement d'une centrale thermique sur la production

primaire planctonique du port de Dunkerque. In Journées de la Thermo-Ecologie 145.

Khalanski M. & Gras R., 1996. Rejets thermiques en rivières et hydrobiologie : Un aperçu sur

l'expérience française : L'hydrobiologie. Houille blanche, 5: 13-18.

Lardicci C., Rossi F. & Maltagliati F., 1999. Detection of thermal pollution: variability of

benthic communities at two different spatial scales in an area influenced by a coastal power

station. Mar. Pollut. Bull., 38(4): 296-303.

López-Galindo C., Garrido M.C., Casanueva J.F. & Nebot E., 2010. Degradation models and

ecotoxicity in marine waters of two antifouling compounds: sodium hypochlorite and an

alkylamine surfactant. Sci. Total Environ., 408(8): 1779-1785.

McCauley J.E., Parr R.A. & Hancock D.R., 1977. Benthic infauna and maintenance dredging:

A case study. Water Res., 11(2): 233-242.

17

Mexel S.A., 2010. MSDS Mexel 432/336/0 version 5.2. 7.

Muxika I., Borja Á. & Bald J., 2007. Using historical data, expert judgement and multivariate

analysis in assessing reference conditions and benthic ecological status, according to the

European Water Framework Directive. Mar. Pollut. Bull., 55(1-6): 16-29.

Pawlik J.R. & Butman C.A., 1993. Settlement of a marine tube worm as a function of current

velocity : interacting effects of hydrodynamics and behavior. Limnol. Oceanogr., 38(8): 1730-

1740.

Pruvot C., Empis A. & Dhainaut-Courtois N., 2000. Présence du mollusque bivalve Corbula

gibba (Olivi, 1792) dans les sédiments meubles du port Est de Dunkerque (Mer du Nord).

Bull. Soc. zool. Fr., 125(1): 75-82.

Teixeira T.P., Neves L.M. & Araújo F.G., 2009. Effects of a nuclear power plant thermal

discharge on habitat complexity and fish community structure in Ilha Grande Bay, Brazil.

Mar. Environ. Res., 68(4): 188-195.

18

Figure 1: Points d’échantillonnage autour de la central électrique du Havre - Sampling

stations around the Le Havre Power Plant Figure 2 : Richesse mesurée aux différentes stations d’échantillonnage en 2000, 2006, 2009 et

20012 - Richness measured at the different sampling stations in 2000, 2006, 2009 and 2012

Figure 3: Densité d’organismes mesurée aux différentes stations d’échantillonnage en 2000,

2006, 2009 et 20012 - Density of organisms measured at the different sampling stations in

2000, 2006, 2009 and 2012. Figure 4: Index biotique marin (AMBI) mesuré aux différentes stations d’échantillonnage en

2000, 2006, 2009 et 20012 - Marine Biotic Index (AMBI) measured at the different sampling

stations in 2000, 2006, 2009 and 2012

Table I: Besoin en eau de refroidissement et élévation maximale de la temperature de l’eau

des trois tranches de la central électrique du Havre - Cooling water requirements and

maximum temperature increase in the three units at the Le Havre power plants Table II : Nombre d’échantillon de sédiment réalisé par champagne pour l’évaluation des

organismes benthiques - Number of sediment samples processed by campaign for benthic

organisms evaluation Table III : Organismes benthiques présents dans les différents échantillons – Composition of

benthic organism of the different samples Table IV : Biomasse totale et contribution des taxons épibenthiques et endobenthiques

dominants par station (échantillonnage effectué en 2012) - Total biomass and contribution of

the dominant epibenthic and endobenthic taxon per station (2012 sampling) Table V : Pourcentage des animaux de chaque groupe écologique observé dans les différents

échantillons de sédiment - Percentage of animals of each of ecological group observed in the

different sediment samples

19

Figure 1: Points d’échantillonnage autour de la central électrique du Havre - Sampling stations around

the Le Havre Power Plant

20

Figure 2 : Richesse mesurée aux différentes stations d’échantillonnage en 2000, 2006, 2009 et 20012 -

Richness measured at the different sampling stations in 2000, 2006, 2009 and 2012

Years with the same letter were not significantly different

21

Figure 3: Densité d’organismes mesurée aux différentes stations d’échantillonnage en 2000, 2006, 2009 et

20012 - Density of organisms measured at the different sampling stations in 2000, 2006, 2009 and 2012.

Stations with the same letter were not significantly different

22

Figure 4: Index biotique marin (AMBI) mesuré aux différentes stations d’échantillonnage en 2000, 2006,

2009 et 20012 - Marine Biotic Index (AMBI) measured at the different sampling stations in 2000, 2006,

2009 and 2012

23

Table I: Besoin en eau de refroidissement et élévation maximale de la temperature de l’eau des trois

tranches de la central électrique du Havre - Cooling water requirements and maximum temperature

increase in the three units at the Le Havre power plants

Nominal

Power

(Mwe)

Cooling

Water flow

(m3s

-1)

Maximum

Temperature

rise (°C)

Anti-fouling treatments

Continuous

chlorination Mexel

® 432/0 Mexel 432/336/0

Unit 1 250 9 8 Before 1996 1996-2008

Since 2008 Unit 2 600 22 9 Before 1997 1997-2008

Unit 4 600 22 9 Before 2006 2006-2008

Table II : Nombre d’échantillon de sédiment réalisé par champagne pour l’évaluation des organismes

benthiques - Number of sediment samples processed by campaign for benthic organisms evaluation

Date Station

1a 1b 1c 2 3 4 5 6 7 20

th of December

2000 2

1 1 1 1 1 1 1

14th

of June 2006 61

61

61

61

61

61

29th

of May 2009 31

31

31

31

31

31

11th

of June 2012 3 3 3 3 3 3

1 Sediment samples gathered before benthic organism identification

24

Table III : Organismes benthiques présents dans les différents échantillons – Composition of benthic organism of the different samples P

hy

lum

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

An

nel

ida

Cli

tell

ata Oligochaeta 5

7

10

Tubificoides sp. 5

967 150 1553 2213 37 587

Po

lych

aeta

Nereidae

No

t as

sig

ned

10

Polychaete 7

Polychaete sp. C

27

Po

lych

aeta

err

anti

a

Anaitides maculata 2

20 53

120

3

3

Eteone longa 3

30 3

13

Exogone naidina 2

3

Flabelligera affinis 2

373

13 183

Gattyana cirrhosa 3

10

10

Glycera fallax 2

3

Glycera tridactyla 2

3

Harmothoe impar 2

3

Harmothoe sp, 2

3

10

Lumbrineris

gracilis 2

3

Malmgreniella sp, 2

3

Marphysa

sanguinea 2

80

10

10

3 3

3

13

25

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

An

nel

ida

Po

lych

aeta

err

anti

a

Neanthes succinea 2

40 13

Nephtys cirrosa 2

17

3

Nephtys hombergii 2 67

103 60

60

17

3

157 37

Nephtys

kersivalensis 2

3

7 23 7

Nephtys sp. 2

3

Nereis diversicolor 3

180

10

40 40

83 13

10 3

Perinereis

cultrifera 3

10 280

3

7

Pholoe baltica 1

3

40 10

Pholoe inornata 4

13 3

7 3 7

Phyllodoce

lamelligera 2

3

Phyllodoce mucosa 3

63 3

50

Sphaerodorum

gracilis 2

3

Sphaerosyllis sp. No

t

assi

gn

ed

3

Sthenelais boa 2

3 3

Syllidae No

t

assi

gn

ed

13

26

P

hy

lum

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

An

nel

ida

Po

lych

aeta

erra

nti

a

Syllidia armata 2

7

Syllis gracilis 2

10

Typosyllis

prolifera 2

680

Po

lych

aeta

sed

enta

ria

Ampharete

finmarchica 1

3 67 13

Amphiglena

mediterranea 1

110

7

Amphitrite

johnstoni 1

3

Capitella capitata 5

230 60

20 7370

10

250

83 60

157 27 10 10

17

Capitella sp. 5

7 3

Caulleriella alata 4

3

3 7

Chaetozone gibber 4

7 3 20

867 160

Chaetozone setosa 4

17

Cirratulidae 4

3

7

Cirratulus cirratus 4

17 23

Cirratulus sp, 4

10

Cirriformia

tentaculata 4 7 2540 350 8180

630

1020 4850

3530 4310 50 14000 11873 1973 1583 7333 1900 70 613 17 1647 3 43

Dipolydora

caulleryi 4

10

Euchone rosea 2

53 7 113 13 2690 249

7

27

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

An

nel

ida

Po

lych

aeta

sed

enta

ria

Ficopomatus

enigmaticus 3

20

50

73 23

Hydroides ezoensis 3

3

3

Lagis koreni 4

10

27 3 10

50 40

33 77 17

13 17 7

3 3

Malacoceros

fuliginosus 5

467

33

Manayunkia sp. 3

3

Mediomastus

fragilis 3

7

53 17 20

Melinna palmata 3

30

637 37

Monticellina sp. 4

3

Notomastus

latericeus 3

3

3

Pherusa plumosa 3

3

Polydora ciliata 4

43

Polydora hoplura 4

110

Polydora sp. 4

10760

1550

Protocirrineris

chrysoderma 4

27

3

Pseudopolydora

antennata 4

13 10

Pseudopolydora

pulchra 4

7 3

Pygospio elegans 3

160

Sabella pavonina 1 180

13 150

700 70 5890

50 1970

28

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

An

nel

ida

Po

lych

aeta

sed

enta

ria

Scalibregma

celticum 3

3

Scalibregma

inflatum 3

110 7

33

Spio sp. 3

10

Spirobranchus

lamarcki 2

13

223

Spirobranchus sp. 2

3

113

Spirobranchus

triqueter 2

3

157

Streblospio

benedicti 3

17

3 30

Streblospio

schrubsholi 3

100

Terebellides

stroemii 2

7

Tharyx sp. 4

13 73

3 47 323

Art

hro

pod

a

Co

pep

od

a

Copepoda

Igno

red

3

Mal

aco

stre

aca

Abludomelita

obtusata 3

7 7

Ampelisca sp. 1

7

Ampelisca spinipes 1

3

3

Ampelisca

tenuicornis 1

3

3 20

29

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

Art

hro

pod

a

Mal

aco

stre

aca

Bodotria

scorpioides 2

3 7

3

Bodotria sp. 2

10

Carcinus maenas 3

10

3 3 7 3

Cheirocratus

intermedius 1

7

Corophium

volutator 3

3

77 167 13

Crangon crangon 1

10 63 7

3

40 20

3

Diastylis bradyi 2

20

3

3

Diastylis rugosa 1

10 7 3

Eudorella

truncatula 1

3

Eurydice pulchra 1

7

Jassa falcata 5

3

Jassa marmorata 5

430

20 10

3 3

7

7 7

Liocarcinus

depurator 1

10

Megalope No

t

assi

gn

ed

7

3

Pagurus sp. 2

3

Pariambus typicus 3

3

37

30

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

Art

hro

pod

a

Mal

aco

stre

aca

Phoxocephalidae 1

30 13

3 13

Pilumnus hirtellus 1

10

Pinnotheres pisum No

t

assi

gn

ed

17

Praunus inermis 1

3

Thoralus cranchii 1

3

Max

illo

pod

a

Balanus crenatus

Igno

red

50 40

227

97

Elminius modestus 2

27

Py

cnog

on

ida

Anoplodactylus

pygmaeus 2

290

31

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

Ch

aeto

gn

ath

a

Chaetognatha

Igno

red

3

Ch

ord

ata

Act

ino

pte

ryg

ii

Solea solea

No

t as

sig

ned

3

Ch

ord

ata

Act

ino

pte

ryg

ii Aphia minuta

Igno

red

3 3

7

Pleuronectidae No

t

assi

gn

ed

3

Asc

idia

cea Molgula

manhattensis 1

10

Styela clava 2

40

32

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

Ch

ord

ata

Ost

eich

thy

es

Gobiusculus

minutus

Igno

red

3

Cn

idar

ia

An

tho

zoa Anthozoa 2

103 7 447 83 10

Cereus

pedunculatus 1

4000 100 7

30

130

20 170 57 7 13 13 50 93

Ech

ino

der

mat

a

Ech

ino

idea

Echinocardium

cordatum 1

3

Ech

ino

der

mat

a

Op

hiu

roid

ea

Amphipholis

squamata 1

70

10

10 3 3

3

Amphiura chiajei 2

3

Amphiura

filiformis 2

3

Ophiolepidae No

t

assi

gn

ed

10

Ophiura affinis 2

7

33

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

Fo

ram

inif

era

No

do

sari

ata

Lagena sp.

No

t as

sig

ned

40

Mo

llu

sca

Biv

alv

ia

Abra alba 3 87 20

140 20 50 1010 280 310 10 30 15470 613 520 240

7 703 10 7 80 27 1227 110

Abra prismatica 3

210

13

17

Abra tenuis 3

30

160

Acanthocardia

echinata 1

20

Cerastoderma

edule 3

153

20

40

10

430

20

3

Corbula gibba 4 227 10 10

123 30 120

510

230 440 53 37 20

43 20

7 3

Ensis ensis 1

3 3 7

Kurtiella bidentata 3

20 13

Mytilus edulis 3

83

200

580 1050

17 13 13 10 7

500

23

Nucula nitidosa 1

3 107 3 1743 13

Nucula turgida 1 43 20

503

10 30 100

10 2600 93 163 63

27 1660

Phaxas pellucidus 1

3 13 3

17

70 10

Scrobicularia

plana 3

3

Tapes decussatus 1

10 10

3

3

Tellina pusilla 1 20

20

3 10 40

34

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

Mo

llu

sca

Gas

tro

pod

a

Crepidula

fornicata 3

30

20

3 7

10

230

Epitonium clathrus 1

10

Hinia incrassata 2

240 20 7 33 17 17 7 20

Hinia reticulata 2

40

40

160 130

140 110 50 23 47 97 60 30

Hydrobia ulvae 3

3

Littorina littorea 2

10 10

50

50 7 7

63 60

Littorina obtusata 2

40

Littorina saxatilis 2

10

Nassarius

incrassatus 2

3

Nassarius

reticulatus 2

100 47 63 20 3

Pyramidella sp. 1

3

Turbonilla lactea 1

83

Nem

ato

da

Nematoda 3

90 170 7 40

Nem

erte

a

Nemertea N

ot

assi

gn

ed

113 7 63 3 3

35

Ph

ylu

m

Cla

ss

Taxa

Eco

log

ical

gro

up

2000 2006 2009 2012

Sampling station

1a 1c 3 4 5 6 7 1a 1c 1b 3 4 5 1a 1b 1c 3 4 5 1a 2 3 4 5 6

Pla

tyh

elm

inth

es

Rh

abd

ito

ph

ora

Oligocladus

sanguinolentus

No

t as

sig

ned

40

36

Table IV : Biomasse totale et contribution des taxons épibenthiques et endobenthiques dominants par station (échantillonnage effectué en 2012) - Total biomass and

contribution of the dominant epibenthic and endobenthic taxon per station (2012 sampling)

Station

1a 2 3 4 5 6

Biomass (g.m-2

) 15.2503 68.4853 4.6713 64.8113 20.7763 2.2687

Dominant species

(contribution %)

Epibenthos

Nassarius

reticulatus (49%)

Carcinus maenas

(43%)

Mytilus edulis (82%)

Nassarius reticulatus

(6%)

Nassarius

reticulatus

(86%)

Crepidula fornicata

(36%)

Mytilus edulis

(30%)

Anthozoa

(36%)

Dominant species

(contribution %)

Endobenthos

Oligochaeta

(1.6%)

Cirriformia

tentaculata (6%)

Cirriformia

tentaculata

(4%)

Nucula nitidosa

(3%)

Cirriformia

tentaculata (25%)

Abra alba (6 %)

Acanthocardia

echinata (21%)

Nucula nitidosa

(14 %)

Euchone rosea

(38%)

Nephtys hombergii

(19%)

Abra alba (15%)

37

Table V : Pourcentage des animaux de chaque groupe écologique observé dans les différents échantillons

de sédiment - Percentage of animals of each of ecological group observed in the different sediment samples

Station Year Ecological group

I II III IV V

1a 2012 1 9 14 7 69

1a 2009 2 1 4 93 0

1a 2006 26 2 36 36 0

1a 2000 38 10 14 37 0

1b 2009 1 2 3 94 0

1b 2006 83 2 7 7 0

1c 2009 4 3 11 79 3

1c 2006 2 3 10 84 0

1c 2000 1 0 1 98 0

2 2012 3 10 36 36 10

3 2012 6 10 7 3 74

3 2009 1 6 8 81 3

3 2006 2 0 14 78 6

3 2000 65 17 0 6 11

4 2012 0 18 8 31 41

4 2009 2 2 3 93 0

4 2006 1 8 19 72 0

4 2000 1 1 3 94 1

5 2012 25 38 25 12 1

5 2009 28 5 12 55 0

5 2006 22 1 75 2 0

5 2000 44 12 32 11 0

6 2012 2 61 7 14 15

6 2000 17 6 2 72 2

7 2000 2 2 3 3 90

Mean 15.2 9.2 14.1 47.9 13.1