**3.5. Diversity**

highly significant (*F* = 5.317; *df* = 9; *p* < 0.0001). In the bank of lakes, amphipods were collected

Concerning sebkhas, among 30 sebkhas studied, talitrids were found in only four sebkhas namely: El Ouafi, Maâmoura, Moknine and Gargour. Species richness was equal to one species in the bank of sebkhas El Ouafi and Maâmoura namely *Orchestia gammarellus* and *Talitrus saltator*, respectively. In two other sebkhas, *Orchestia gammarellus* and *Orchestia medi-*

For wadis, individuals were collected only in six wadis among the 41 stations prospected. Species richness varies from one (El Fared wadi, Laakarit wadi, Khniss wadi and Lebna wadi)

A total of 340 specimens of amphipoda Talitridae were collected in lagoons. The bank of Bizerte lagoon revealed statistically the most important relative abundance of amphipod community (36.04%) (Anova test: *F* = 5.330, *df* = 9, *p* < 0.0001). Moreover, in this station, *Orchestia mediterranea* was the most abundant species (25.7%). However, in the banks of El Bcherliya, the Ghar El Melh old harbour, Tunis north and south lagoons, it was rather *Orchestia gammarellus* that dominated. These two species have the same relative abundance (46.7%) in bank of Sidi Ali Mekki lagoon. In Bhiret El Biben lagoon, *Orchestia montagui* was the most abundant species (28.3%). The Anova test revealed that differences between the different lagoons were highly significant (*F* = 7.922; *df* = 7; *p* < 0.0001). The mean community density varied between 0.5 ind.m−2 in the bank of El Bcherliya and 241.5 ind.m−2 in that of Bizerte lagoon. Furthermore, our results showed that *Orchestia mediterranea* presented the most important density in the bank of Bizerte lagoon (62 ind.m−2). Whereas, in the bank of El Bcherliya, Ghar El Melh old harbour, Tunis north and south lagoons, it was *Orchestia gammarellus* that exhibited the largest density with, respectively, 0.5, 19, 34 and 34.5 ind.m−2. These two species were recorded with the same mean density in the bank of Sidi Ali Mekki lagoon (3.5 ind.m−2). In lakes, 170 individuals were collected where *Orchestia mediterranea* presented the highest abundance (26.5%)

In sebkhas, 352 specimens of amphipods were collected. Sebkha Gargour revealed the highest relative abundance (50%) followed by sebkha Moknine which abundance was equal to 34.66%. However, in the bank of the two other sebkhas, the abundance was relatively low in Mâamoura with 15.06% and very low in sebkha El Ouafi with 0.28%. The Anova test revealed a highly significant difference in relative abundance between these sebkhas (*F* = 8.288, *df* = 29, *p* < 0.0001). The relative abundance of *Orchestia gammarellus* and *Talitrus saltator* were maximal (100%), respectively, in sebkha El Ouafi and Mâamoura since each sebkha harbours only one species. In Moknine, abundance was greater for *Orchestia gammarellus* (53.3%) than in *Orchestia mediterranea* (46.7%) and inversely in the sebkha Gargour where the highest abundance was recorded for *Orchestia mediterranea* with 59.1%. In addition, no significant difference in relative abundance between species was found (Anova test: *F* = 1.461, *df* = 2, *p* = 0.233). The global mean density oscillated between 0.5 ind.m−2 in sebkha El Ouafi and 88 ind.m−2 in sebkha Gargour. The study of the mean density per species showed a very low density of

to six species (El Korsi). In hill lakes and dams, no species were collected.

only in Ichkeul lake (*S* = 5).

110 Selected Studies in Biodiversity

*terranea* were collected.

and density (22.5 ind.m−2).

**3.4. Relative abundance and density**

According to the Simpson index (Is), the most important diversity was observed in the Bizerte lagoon where we noted the highest value which tends towards the specific richness (6.059) and the community was more balanced in Boughaz.

In Ghar El Melh old harbour, we obtained the lowest diversity compared to that observed in Boughaz. This result could be explained by the fact that this index does not consider rare species into account.

The Shannon-Weaver (H') index ranged from 1.287 in the bank of Sidi Ali Mekki lagoon to 2.771 in the bank of Bizerte lagoon where the diversity was relatively significant. This index, which takes into account the rare species, was often accompanied by the equitability index, which was more or less insensitive to specific richness. It ranged from 0.812 (Sidi Ali Mekki) to 0.996 (Boughaz) where the community was more balanced.

In the banks of different sebkhas, we did not observed a great diversity, so the analysis of diversity was not carried out.

In wadis, results showed that the Simpson index varies between 1 in the Lebna wadi estuary, Khniss, Laakarit and El Fared wadis and 5.78 in El Korsi station where we found the highest species richness (*S* = 6). The Shannon-Weaver index confirmed the previous index showing that the most important diversity was observed in El Korsi station (*H*′ = 2.56). Moreover, the study of the equitability index showed that the community was more balanced in this station (*J*′ = 0.99) where species were equitably distributed.

#### **3.6. Amphipod distribution according to environmental factors and wetland types**

To better understand the species distribution in the different wetland types and to elucidate the parameters involved in their distribution, a canonical correspondence analysis was carried out (**Figure 2**). The first three axes, F1, F2 and F3 extract, respectively, 71.43, 20.23 and 5.55% of the variance. The two species, *Orchestia mediterranea* and *Orchestia gammarellus* that dominated the majority of lagoons and sebkhas were positively correlated with the strontium content and negatively with concentrations of vanadium, chromium, manganese, cobalt, nickel, copper, zinc, arsenic, rubidium, cadmium, thallium and lead. However,

the banks of Tunisian wetlands where many species were found in sympatry with amphipods, a positive correlation between species richness and altitudinal gradient has been highlighted [43]. The same authors showed that species richness differs significantly depending on wetland types

Biodiversity of Amphipoda Talitridae in Tunisian Wetlands

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A total of 2420 amphipods belonging to different species were determined in all prospected wetlands; more than half of the specimens were collected in lagoons (*N* = 1340) with a mean density of 241.5 ind.m−2 observed in the bank of the Bizerte lagoon; *Orchestia mediterranea* showed the most important density in this lagoon. In sebkhas and wadis, the highest densities were recorded, respectively, in sebkha Gargour and El Korsi where *Orchestia mediterranea* and *Platorchestia platensis* were characterized by the highest density, respectively. Studying *Talitrus saltator* and *Britorchestia brito* populations in Zouara beach, Charfi-Cheikhrouha et al. [26] determined a mean density equal to 262.94 ± 85 ind.m−2. These authors showed that the density increased in autumn and winter and reached a maximum in March for *Talitrus saltator*; while for *Britorchestia brito*, this density increased from the middle of March and peaked in October. In Algeria, in the bay of Bou Ismail, *Orchestia montagui* and *Deshayesorchestia deshayesii* reached more than 45,000 ind.m−2 [44]. In the Bou Regreg estuary, *Orchestia mediterranea* showed densities ranging from 3380 (February) to 7000 ind.m−2 (August) [45]. Studying the spatio-temporal distribution of amphipods in different wetlands in Tunisia, Jelassi [46] highlighted that the most important densities were

The diversity of the different talitrid species was related to the presence of different parameters. This relation depends on the wetland type; for example, in lagoons, the sandhopper *Talitrus saltator* was correlated with climatic (temperature, humidity) as well as edaphic factors (organic matter, granulometry, heavy metals of soil) whereas in sebkhas and wadis, this species was correlated only with edaphic factors. These results were also observed for other species. In this context, several studies have investigated the role of environmental factors and have revealed the influence of some factors rather than others. Jelassi et al. [31] have shown that talitrid abundance in the bank of Bizerte lagoon was closely related to air temperature. Bouslama et al. [47] showed that temperature was the important factor influencing the zonation whose augmentation induces the displacement or the migration of *Talitrus saltator* population from the top to the bottom of the beach. This result was similar to that found by Fallaci et al. [48], who indicated that mean zonation of this species was influenced by temperature during its activity period. Other authors such as Colombini et al. [49] confirmed the importance of sediment parameters in the selection of specific distribution area especially for young individuals. Our results showed that the two species *Orchestia cavimana* and *Platorchestia platensis* were correlated with organic matter. Jelassi et al. [32] highlighted that air and soil temperature were the best predictors for *O. stephenseni* abundance that negatively corresponded with the proportion of fine sand fraction and organic matter content of the soil. *O. montagui* and *O. cavimana* abundances corresponded positively with air humidity and the soil lithium and rubidium contents, but negatively with the soil tin content and the proportion of the silt and clay fraction. *D. deshayesii* and *P. platensis* did not exhibit any clear correspondence

or bioclimatic zones.

observed during spring.

with station characteristics.

**Figure 2.** Canonical correspondence analysis (CCA) performed on the abiotic parameters. Om: *Orchestia montagui*, Og: *Orchestia gammarellus*, Omed: *Orchestia mediterranea*, Os: *Orchestia stephenseni*, Oc: *Orchestia cavimana*, Pp: *Platorchestia platensis*, Ts: *Talitrus saltator*, Dd: *Deshayesorchestia deshayesii*, Hsol: soil humidiy, Tsol: soil temperature, Gra: granulometry, V: vanadium, Cr: chromium, Mn: manganese, Co: cobalt, Ni: nickel, Cu: copper, Zn: zinc, As: arsenic, Cd: cadmium, Sn: tin, Tl: thallium, Pb: lead, Li: lithium, Rb: rubidium and Sr: strontium.

*Talitrus saltator*, abundant species in El Korsi and the estuary of Lebna wadi, as well as *Orchestia stephenseni* and *Deshayesorchestia deshayesii* were positively correlated with temperature and humidity. In the third axis, *Orchestia cavimana* and *Platorchestia platensis* were found positively correlated with organic matter and negatively with lithium and tin content.
