diversity of terrestrial isopods in the supralittoral zone of ghar el melh lagoon (tunisia)

Diversity of terrestrial isopods in the supralittoral zone ofGhar El Melh lagoon (Tunisia)

Hajer Khemaissia1*, Raja Jelassi1, Catherine Souty-Grosset2 and KarimaNasri-Ammar1

1Unite de recherche Bio-Ecologie et Systematique Evolutive, Faculte des Sciences de Tunis, El Manar II 2092, Tunis, Tunisie and 2Universite de

Poitiers, Laboratoire Ecologie et Biologie des Interactions, Equipe Ecologie Evolution Symbiose, UMR CNRS 7267, 40 avenue du Recteur Pineau,

F-86022, Poitiers Cedex, France

Abstract

In Tunisia, while wetlands are considered as remarkable

habitats for their faunal and floral diversity, few studies on

the species diversity of terrestrial isopods were performed.

To fill this gap, the spatio-temporal distribution of Onisci-

dea at Ghar El Melh lagoon (north-east of Tunisia) was

analysed. Sampling was carried out with 50 9 50 cm

quadrats along a perpendicular transect to the shoreline.

Nine species of terrestrial isopods belonging to seven

genera were identified. Chaetophiloscia elongata Dollfus,

1884 was the most abundant species in all seasons except

for summer; its relative abundance ranged from 38.9% to

77% in summer and autumn, respectively. Hill diversity

indices ranged from 0.86 to 0.94 and equitability indices

from 0.33 and 0.68. The statistical analysis showed a

significant difference of isopod species and plant associa-

tions among seasons.

Key words: biodiversity, distribution, Ghar El Melh lagoon,

Oniscidea, supralittoral zone

Resume

En Tunisie, si les zones humides sont considerees comme

des habitats remarquables pour leur diversite faunistique

et floristique, peu d’etudes ont ete faites sur la diversite des

isopodes terrestres. Pour combler cette lacune, nous avons

etudie la distribution spatio-temporelle des Oniscidea de la

lagune de Ghar El Mehl (au nord-est de la Tunisie).

L’ echantillonnage a ete effectue avec un quadrat

50 x 50 cm, le long d’un transect perpendiculaire a la

ligne de rivage. Neuf especes d’isopodes terrestres appar-

tenant a sept genres ont ete identifiees. Quelle que soit la

saison, Chaetophiloscia elongata Dollfus, 1884 est l’espece la

plus abondante exception faite pour la saison d’ete; son

abondance relative varie de 38,9 a 77 % en ete et en

automne respectivement. L’indice de diversite de Hill varie

de 0,86 a 0,94 et l’equitabilite de 0,33 a 0,68. L’analyse

statistique montre une difference significative de la

distribution saisonniere des isopodes terrestres en fonction

des associations vegetales

Introduction

In the Mediterranean, wetland areas are of great impor-

tance in conservation biology. They offer a wide variety of

natural habitats for both plants and animals and are

considered among the most biologically diverse and

productive ecosystems (Medail & Quezel, 1999). The

interactions of biological and physicochemical components

of a wetland, such as soil types, water, plants and animals,

enable the wetland to perform many ecological functions,

for example, shoreline stabilization and water purification.

Wetlands are breeding sites and wintering grounds for

millions of birds (Elmberg et al., 1994) but also they

provide a place for a number of birds to feed and rest

during their annual migrations between Africa and

northern Europe and Asia (Cramp & Simmons, 1983).

However, wetlands are particularly sensitive and there-

fore vulnerable to the potential impacts of climate change.

Indeed, biodiversity is threatened by the degradation,

destruction and even disappearance of large amounts of

wetland surface, due to various anthropogenic activities

especially urbanization, roadways, pollution and agricul-

tural practice. Losses of the Mediterranean wetlands were*Correspondence: E-mail: [email protected]

348 © 2012 Blackwell Publishing Ltd, Afr. J. Ecol., 51, 348–357

estimated at 60% in Spain in 1990 (Bifani, Montes &

Casado, 1992), about 75% in Italy between 1865 and

1972 (Hollis et al., 1992) and at minimum 61% in Greece

between 1910 and 1990 (Handrinos, 1992; Psilovikos,

1992). In Tunisia, it is estimated that 84% of wetlands in

the Medjerda catchment areas disappeared during the

20th century.

An important source of biodiversity that is being affected

is soil biodiversity. The majority of this soil fauna involves

arthropods that occupy the widest diversity of microhab-

itats and niches and play more ecological roles than other

group of animals. Among soil animals, oniscideans are

important players in soil ecology particularly in the

regulation of organic matter and nutrients; 10% of the

annual litter is fragmented by isopods (Hassall & Sutton,

1978; Jambu, Juchault & Mocquard, 1987; Mocquard

et al., 1988). However, they are very sensitive to changes

in their habitats and respond differently, depending on the

species, to the physical, chemical and biological

environment. Indeed, isopods have preferences in terms

of pH (Van Straalen & Verhoef, 1997), calcium levels,

moisture content (Zimmer et al., 2000) and vegetation

type (Hassall & Rushton, 1985). According to Van

Straalen et al. (2001), terrestrial isopods are also among

the most efficient bioaccumulators of heavy metals. They

have developed physiological mechanisms for regulating

the content of heavy metals, which allow them to survive

at high levels in the litter and soil. Oniscus asellus and

Porcellio scaber, for example, provide information on the

degree of soil contamination by zinc and cadmium

(Hopkin, Jones & Dietrich, 1993; Godet et al., 2011); it is

also the case for Porcellio laevis (Hussein et al., 2006) and

Porcellio dilatatus (Calhoa, Soares & Mann, 2006).

In the biogeographical and ecological literature, terres-

trial isopods exploiting mountains’ habitats, agricultural

grassland and natural parks have been studied (e.g.

Schmalfuss & Ferrara, 1982; Sfenthourakis, Anastasiou

& Strutenshi, 2005; Souty-Grosset et al., 2005a,b; Sfen-

thourakis, Orfanou & Anastastiou, 2007). Their biology,

population dynamics and biodiversity have been examined

in Tunisia and studied in comparison with other Mediter-

ranean and Atlantic populations. Their diversity in coastal

areas of the sandy beaches was studied (Colombini et al.,

2003; Achouri, Hamaied & Charfi-Cheikhrouha, 2008a);

however, the communities of terrestrial isopod inhabiting

the supralittoral zones effectively started with the study of

Jelassi, Khemaissia & Nasri-Ammar (2012) conducted on

the spatio-temporal distribution of Amphipoda and

Oniscidea at Bizerte lagoon. In this perspective, the aims

of the present analysis were to establish a list of Oniscidea

species collected in the supralittoral zone of Ghar El Melh

lagoon, to analyse their distribution and to estimate species

richness, abundance and seasonal variation.

Materials and methods

Study site

The lagoon complex of Ghar El Melh is situated in

north-east Tunisia, on the north-western side of the Gulf

of Tunisia. It is composed of the lagoon of Ghar El Melh,

the lagoon of Sidi Ali El Mekki and the sebkhat of El

Ouafi (Fig. 1). A sebkhat, commonly found in North

Africa, is defined as a saline flat or salt-crusted depres-

sion. The lagoon of Ghar El Melh has an elliptical shape

of approximately 28.5 km2 and an average depth of

0.8 m. The coastal barrier separating the lagoon from

the Mediterranean Sea was interrupted, allowing a

permanent hydraulic communication with the sea across

a local opening of 85 m wide and an average depth of

2.5 m named El Boughaz. The sampling site is situated

in the supralittoral zone of Ghar El Melh lagoon, at the

old harbour (37°10′N, 10°11′E). It was characterized by

a vegetation that consists of Obione portulacoїdes (L.)

Aellen and Salicornia arabica (L.) and by a loamy sand

substrate.

Sampling method

Four samples were made during 1 year in winter (Janu-

ary), spring (April), summer (July) and autumn (Novem-

ber) 2009. The collection of isopods was performed

manually using a square quadrat of 50 cm per side.

Quadrats were placed successively, along a perpendicular

transect, from the shoreline to the road. For each season,

one transect was studied; its length was equal to 25

(50 quadrats), 23.5 (47 quadrats), 22.5 (45 quadrats)

and 21 m (42 quadrats) in spring, summer, autumn and

winter, respectively (Fig. 2). Sampling was realized by two

persons in the morning, and 10 min were devoted for each

quadrat. The animal contents of each quadrat (5 cm

depth) were preserved in 70 % ethanol. In the laboratory,

specimens of terrestrial isopods were identified using a

stereomicroscope Leica MS 5 (Meyer instruments, Hous-

ton, TX, USA) then counted.

© 2012 Blackwell Publishing Ltd, Afr. J. Ecol., 51, 348–357

Diversity of terrestrial isopod 349

Soil analysis

Physicochemical analyses were performed on soil sampled

at each season. Three soil samples were taken from a depth

of 0–10 cm. The three samples were collected from three

different points along the transect and then mixed to form

a composite sample. There was at least 5 m between the

sampling points. Each sample was made free of organic

debris and gravel. Once in the laboratory, the following

analyses were made:

1 Soil pH: 5 g of soil previously dried and ground into fine

particles was placed with 12.5 ml of double-distilled water.

The samples were left in contact for 1 h and agitated from

time to time. The values of pH were measured using a

EUTECH instruments pH 510 meter (CyberScan Series,

Asia, Singapore).

2 Soil conductivity: 5 g of soil already dried and ground

into fine particles was brought into contact with 50 ml of

double-distilled water then stirred for 10 min twice each

time. After standing all night, we proceeded to read the

conductivity of the soil solution using a Multi-parameter

InstrumentsMulti-340i/SET (Expotech, Houston, TX, USA).

3 Soil sodium and calcium contents were determined by

atomic absorption technique based on the methodology of

the IC2MP (Institute of Chemistry of Poitiers: materials and

natural resources). To obtain a usable sample, we put 5 g of

soil in 50 ml of distilled water. After 1 h, the solution was

11 m 50 3 m 9 m 501 m

7 m 50 2 m 50 11 m 502 m

6 m 1 m 50 13 m 2 m

5 m 50 15 m0.5 m

Spring

Summer

Autumn

Winter

Seasons

Shoreline Transect (m)

Fig 2 Topology profile along the studied transect based on plant association: zone 1 (Cymodocea) ; zone 2 (Salicornia arabica and Obione

portulacoides) ; zone 3 (Obione portulacoides) ; zone 4 (dry ground zone)

Ghar El MelhLagoon

Sidi Ali El Mekki Lagoon

Sebkhat El Ouafi

MEDITERRANEAN SEA1 km

N

80 km30º

32º

34º

36º

38º

10º8º 12º

N

: Sampling site (37° 10' N, 10° 11' E)

Fig 1 Map of Tunisia and location of the sampling site


350 Hajer Khemaissia et al.

filtered through a 50-lmmesh. To obtain reliable measure-

ments, it was necessary to carry out successive dilutions.

4 Humidity and temperature of air and soil were

measured in situ at each season using a thermo-

hygrometer.

Data analysis

To analyse the Oniscidea community, the following

ecological indices were used: (i) species richness, expressed

by the number of species encountered at each season;

(ii) abundance of individual species, expressed by the total

number of individuals gathered at each season; (iii) the

density of isopods, expressed by the number of individu-

als m�2 calculated in each sampling quadrats along the

transect for the four seasons and (iv) evenness, expressed

by the Hill ratio (Hill = N2/N1) and the Pielou’s evenness

index (J′ = H′/log2 S) where N1 = exponential of Shannon

index (H′); N2 = inverse of Simpson index.

Freidman test, chi-square (v2) and ANOVA were used to

compare theecological indices (relativeabundancealongthe

transect, sex ratio and density per quadrat at each season).

Multivariate analysis was also applied to relate the

species abundance and environmental factors using

canonical correspondence analyses (CCA) performed with

the free version of XLSTAT 2011.5.01 software (http://

www.xlstat.com).

Results

Species richness, relative abundance and diversity

During the four sampling seasons, we collected 1651

terrestrial isopods and identified nine species belonging to

seven genera. Most of them were Chaetophiloscia elongata

(Dollfus, 1884) (64.9%) and P. laevis (Latreille, 1804)

(32.3%). Armadillidium pelagicum (Arcangeli, 1957)

occurred only as a single specimen, others [Porcellio

variabilis (Lucas, 1849), Armadillo officinalis (Dumeril,

1816) and Armadilloniscus ellipticus (Harger, 1878)] were

represented by only two or three specimens. The statistical

analysis revealed a highly significant difference in the

global population abundance among sampling seasons

(P = 0.005; df = 8). Table 1 shows the structure of isopod

populations along the transect; this structure was depen-

dent on identified species, sexes and categories of females.

The number of total female species was significantly higher

than that of males (v2 = 1070.4; P < 0.001; df = 1). For

the two abundant species C. elongata and P. laevis, the sex

ratio was also female biased (v2 = 658.6; P < 0.001;

df = 1 and v2 = 446.3; P < 0.001; df = 1, respectively).

Isopod diversity varied depending on sampling season. In

summer, the Hill index was 0.94, whereas in spring,

autumn and winter, it was 0.85, 0.86 and 0.87,

respectively. The equitability index, 0.68, indicated

uneven quantities of each species in summer. The lowest

value of equitability index, 0.33, was observed in the

autumn season when five species were collected with a

dominance of C. elongata.

Density communities

Densities according to seasons and distances from the

shoreline. The highest overall density was recorded in

autumn (85.8 individual’s m�2), whereas in winter, it

decreased to 15 individual’s m�2 (Table 1). Furthermore,

the highest densities per quadrat were recorded at 1 m from

the supralittoral limit in spring (316 individual’s m�2), at

2.5 m in autumn (1416 individual’s m�2), at 4.5 m in

summer (264 individual’s m�2) and at 9.5 m in winter

(232 individual’s m�2) (Fig. 3). ANOVA test revealed no

significant differences in the seasonal variation in densities

per quadrat when all species were taken into account (P =

0.052; F = 2.62; df = 3). Also, no significant differences

were observed in the seasonal variation in densities per

quadrat for the abundant species P. laevis (P = 0.355; F =

1.89; df = 3) and C. elongata (P = 0.07; F = 2.39; df = 3).

Different seasonal distribution patterns were observed. In

spring, the distribution area was wider than in the other

seasons. Oniscidea being distributed over a distance of

22.5 m, while the distribution area was limited for the both

seasons summerandautumnto7and8.5 m,respectively. In

winter, thedistributionofOniscideawasextendedbutdidnot

exceed 11 m from the shoreline (Fig. 3).

Density according to zones defined according to the type of

vegetation. Based on plant associations, the transect was

subdivided into four zones (zone 1 to zone 4) from the

shoreline (Fig. 2):

Zone 1: shoreline covered mainly by the algae Cymod-

ocea; algae presence varied from 0.5 m width in winter

to 2 m in summer and autumn. In this zone, the

highest mean density of Oniscidea was recorded in

autumn (318 ind. m�2).



Table

1Populationstructure

ofterrestrialisopodsduringthesamplingseasons;(a):Diversity

indices

and(b):Environmen

talfactors

atthestudysite

Spring

Summer

Autumn

Winter

♂R♀

NR♀

Juv

♂R♀

NR♀

Juv

♂R♀

NR♀

Juv

♂R♀

NR♀

Juv

Porcellio

laevisLatreillle,1804

19

13

34

149

4139

312

3184

810

153

0

Chaetophilosciaelongata

Dollfus,1884

38

585

18

18

251

55

105

145

374

103

14

29

26

3

Porcellionides

sexfasciatusBudde-Lund,1885

42

30

00

00

00

00

00

00

Arm

adillo

officinalisDumeril,1816

20

10

00

00

00

00

00

00

Porcellionides

pruinosusBrandt,1833

00

00

10

10

00

20

84

40

Porcellio

variabilisLucas,1846

00

00

00

10

10

00

00

00

LeptotrichuspanzeriiAudouin,1826

00

00

00

00

00

50

20

30

Arm

adilloniscusellipticusHarger,1878

00

00

00

00

10

10

00

00

Arm

adillidium

pelagicum

Arcangeli,1957

00

00

00

00

00

01

00

0

Total

63

20

123

19

68

6192

58

119

148

566

111

35

34

86

3

(a)

Sex

ratio

0.44

0.34

0.17

0.29

Number

ofspecies

44

65

Meanden

sity

(individuals

m�2)

18

27.6

85.5

15.00

Hillindex

0.85

0.94

0.86

0.87

Equitabilityindex

0.59

0.52

0.33

0.68

(b)

Airtemperature

(°C)

22.3

41.8

20.1

16.3

Airhumidity(%

)60

20

63

76

Soilhumidity(%

)62

46

68

70

SoilpH

9.04

8.26

7.96

9

Soilconductivity(m

scm

�1)

0.621

3.56

0.003

0.006

Soilcalcium

content(m

gg�1)

9.238

9.308

5.158

0.095

Soilsodium

content(m

gg�1)

0.198

3.27

0.145

0.09

♂=males;R♀

=reproductivefemales;N

R♀

=nonreproductivefemales;Juv=juven

iles.



Zone 2: covered by only two plants, S. arabica (L.) and

O. portulacoїdes (L.) Aellen; both were found in spring,

summer and autumn seasons, whereas in winter, only

S. arabica was still present. The mean densities of

Oniscidea varied between 19.6 and 205.3 ind. m�2 in

spring and autumn, respectively.

Zone 3: covered only by O. portulacoїdes. In this zone, the

density of Oniscidea varied between0and14.5 ind. m�2

in summer, autumn and winter, respectively.

Zone 4: dry ground zone without vegetation,

12.2 ± 2.3 m wide. In this zone, only some Oniscidea

were collected in winter (10.8 ind. m�2).

The distribution of Oniscidea was statistically significant

with the seasonal variation in vegetation (P < 0.0001;

F = 11.57; df = 3). ANOVA test showed a high statistical

correlation of C. elongata with zone 1 (P < 0.0001;

F = 11.22; df = 3) and of P. laevis with zone 2

(P = 0.0001; F = 5.5; df = 3).

Isopod distribution according to environmental factors

Canonical correspondence analysis was performed to

better understand which of the environmental factors

influenced the seasonal distribution of species (Fig. 4). CCA

analyses showed that species occurrence correlated with

site characteristics: 76% of information was obtained

through the first axis and an additional 15.8% through the

second axis. P. laevis was abundant in the summer and

was clearly associated with soil pH. However, C. elongata,

abundant in spring and autumn, was negatively associated

with soil humidity, conductivity and soil sodium content.

The effects of soil calcium content and of air humidity on

the seasonal distribution of the species Leptotrichus panzerii

(Audouin, 1826), Porcellionides pruinosus (Brandt, 1833),

A. pelagicum, Porcellionides sexfasciatus (Budde-Lund,

1885) and P. variabilis cannot be deduced because the

number of the corresponding species was low.

Discussion

The global analysis of the species richness revealed the

presence of nine species in the supralittoral zone of Ghar El

Melh lagoon, but no large difference was observed between

the four sampling seasons. Species richness was quite high

compared with previous studies on the isopod diversity

both in Zouaraa sandy beach and in three biotopes of the

0

80

160

240

320 Spring

0

500

1000

1500 Autumn

0

80

160

240

320 Summer

0

80

160

240

320 Winter

Den

sity

/m2

Shoreline Transect (0.5 m)Shoreline Transect (0.5 m)

: Distribution area

Fig 3 Seasonal variation of the spatial distribution of terrestrial isopods along the studied transect



supralittoral zone of Berkoukech area (both located in the

north-western coast of Tunisia) when three and seven

species were collected, respectively (Colombini et al., 2003;

Achouri, Hamaied & Charfi-Cheikhrouha, 2008a). Recent

studies conducted in others regions of Tunisia, in the

Kroumirie mountains, showed a species richness of twelve

species in four biotopes of the Berkoukech catchment area

(Achouri, Hamaied & Charfi-Cheikhrouha, 2008a) and

eleven species in nine habitats of wadi Moula-Bouterfess

catchment (Hamaied-Melki et al., 2010).

Moreover, concerning the global analysis of species

abundance, P. laevis, a widespread species in Tunisia

(Medini-Bouaziz, 2002), and C. elongata, a holomediterra-

nean species (Caruso & Lombardo, 1982; Taiti & Ferrara,

1996; Schmalfuss, 2003), were the most frequent species

whatever the sampling season. The highest relative

abundances were recorded in summer for the former

species (60.2%) and in autumn for the latter one (77%). In

a similar study carried out in the supralittoral zone of

Bizerte lagoon (North of Tunisia), C. elongata was also the

most frequent species (Jelassi, Khemaissia & Nasri-Ammar,

2012). Additionally, C. elongata was the most common

species identified and present in all sampling sites situated

in a protected area characterized by a salty coastal ponds

in south-eastern Sicily (Messina et al., 2011) and in four

habitats of Berkoukech area (Achouri, Hamaied & Charfi-

Cheikhrouha, 2008a). In the present study, Armadillo

officinalis and L. panzerii were only seasonally present

along the studied transect. This result is likely due to the

ecological preference of these two species that are gener-

ally found in arid environment (Vandel, 1960). In fact, in

Sicily, these species were collected in the locations situated

far from the sea and ponds reflecting their xerophilous

characteristics (Messina et al., 2011).

If we compare our results with those obtained in salt

marsh habitats of the Ria Formosa lagoon system

(southern Portugal) and among the four species of isopod,

Tylos ponticus was the most abundant species (Dias, Sprung

& Hassall, 2005). However, in studies about macrofauna

communities of sandy beaches, Tylos europaeus was the

most abundant species in the majority of the Mediterra-

nean localities, including studies on the north-western

coast of Tunisia (Colombini et al., 2003), north-eastern

coast of Morocco (Achouri et al., 2008b) and the Maltese

beaches (Deidun et al., 2003), as well as studies on the

Atlantic coasts of Portugal (Goncalves et al., 2009;

Goncalves & Marques, 2011) and north-western Spain

(Rodil, Lastra & Sanchez-Mata, 2006). The observed

Sp SA

W

P. lae

C. el

P. sexA. off

P. var

P. pru

L. pz

A. el

A. pel

Hair

Hsoil

pHsoil

CsoilCasoil

Nasoil

–1,6

–0,8

0

0,8

1,6

2,4

3,2

–2 –1,5 –1 –0,5 0 0,5 1 1,5 2

F2 (1

5.80

%)

F1 (76.04 %)

ACC (axis F1 & F2 : 91.85 %)

Fig 4 Canonical correspondence analysis performed on the biotic and abiotic parameters: A. pel: Armadillidium pelagicum; P. pru:

Porcellionides pruinosus; L. pz: Leptotrichus panzerii; P. lae : Porcellio laevis; C. el : Chaetophiloscia elongata; P. var : Porcellio variabilis; P. sex :

Porcellionides sexfasciatus; A. off : Armadillo officinalis; A. lit : Armadilloniscus ellipticus; Sp: spring; S: summer; A: autumn; W: winter; Casoil:

soil calcium content; Nasoil: soil sodium content; Csoil: soil conductivity; pHsoil: soil pH; Hair: air humidity; Hsoil: soil humidity; □ species;

○ seasons; environmental factors



differences in faunal composition between supralittoral

zone of lagoons and sandy beaches can be probably related

to differences in sediment grain size or to the beach dune

profile and orientation that existent between the two

different ecosystems. It has been shown that the associa-

tion of isopod species with habitat types is strongly affected

by soil and humus types (Judas & Hauser, 1998).

Concerning the variation in species abundance and

density according to the seasons, a fluctuation was

observed confirming the observations by Hornung &

Warburg (1995) on terrestrial arthropod populations in

southern Mediterranean coastal areas. Indeed, our results

showed that mean densities per quadrat ranged between

15 and 85.8 ind. m�2, respectively, in winter and autumn.

For the two abundant species, P. laevis and C. elongata, the

highest mean densities per quadrat were recorded in

autumn season (59.1 and 242.2 ind. m�2, respectively).

When compared with data of Hornung & Warburg (1995),

we showed that the density of C. elongata was higher than

that of the two species Chaetophiloscia sp. collected in the

Mediterranean grassland (0.08 ind. m�2) and oak forest

(0.11 ind. m�2). A possible explanation could be related to

the higher humidity of soil, in the supralittoral zone

compared to other biota, which had a positive influence on

the distribution of isopod species. It was shown that

Philoscia muscorum is sensitive to variations in temperature

(Zimmer et al., 2000) and humidity (Souty-Grosset et al.,

2005a). In the present study, the distribution of Oniscidea

was significantly correlated with the seasonal variation in

plant associations. In a previous study, it was demonstrated

that the highest species diversity was related to the highest

flora diversity (Achouri et al., 2008b).

Finally, the distribution of isopods was investigated

according to environmental factors using CCA analysis.

Our statistical analyses indicated that the variation in the

distribution of isopods depended on some factors like

temperature, humidity and the type of habitat, which is

influenced by soil quality. Brereton (1957) showed that

the differences found in the local distribution of isopods

during the different seasons depended on the nature of the

microhabitats. Despite the fact that the few correlations

between physical parameters and faunal abundances that

we found were generally not well marked, CCA showed

that the distribution of P. laevis was driven by soil pH and

that of C. elongata was negatively correlated with humid-

ity, conductivity and sodium content of the soil. Soil pH

was shown to control the distribution of O. asellus, an

acidophil species, Armadillidium vulgare and Armadillidium

nasatum, which prefer a neutral pH (Van Straalen &

Verhoef, 1997), while for P. muscorum, present in many

forests in Poitou Charentes (France), had a pH preferen-

dum between 5.6 and 6.1 (Souty-Grosset et al., 2005a).

Furthermore, the distribution of Ligidium hypnorum and

Trachelipus rathkii correlated with soil pH, with optima of

4.5 and 6.0, respectively (Zimmer et al., 1999).

Due to their exoskeleton, isopods are generally in need of

Ca2+, but in our study, the distribution of isopod species

may not depend on soil calcium content; however, further

investigations at other sites may give more information

about the impact of this factor on terrestrial isopod

diversity. Zimmer et al. (2000) indicate that calcium is

sufficiently available in many soils to meet the require-

ments of isopods and diplopods.

Acknowledgements

This study was funded owing to the Research Unit of Bio-

ecology and Evolutionary Systematics (UR11ES11), Fac-

ulty of Science of Tunis, University of Tunis El Manar and

the research project N° 07G0918 CMCU Franco-Tunisian

‘Structural diversity of crustacean Terrestrial Isopods bio-

indicators of habitat quality’. We would like to thank Dr.

Julian Reynolds (Trinity College Dublin, Ireland) for

improving English language and Dr. Christelle Roudaut

(Institute of Chemistry of Poitiers: materials and natural

resources) for assistance with soil analysis.

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(Manuscript accepted 07 October 2012)

doi: 10.1111/aje.12043



diversity of terrestrial isopods in the supralittoral zone of ghar el melh lagoon (tunisia)

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