Inventory of the free – living marine nematode species from el Bibane Lagoon ( Tunisia )

espanolSe ha realizado un inventario detallado de los nematodos de vida libre de la parte norte deTunez, pero la parte sur del pais esta inexplorada. La laguna de El Bibane es la segunda mas extensa de Tunez, por lo que su importancia es fundamental para el desarrollo de futuras acciones de conservacion y su biodiversidad debe ser evaluada. Se encontraron 71 especies de nematodos, pertenecientes a 68 generos y 22 familias, registrandose la menor riqueza en la zona central de la laguna, donde se concentran los porcentajes mas elevados de lodo y materia organica. El numero de especies halladas en este estudio es elevado si se compara con el de otros entornos de transicion de la cuenca mediterranea, pero mas bajo que los registrados en el norte de Europa. La mayor parte de las especies son tipicas de entornos de transicion o de sedimentos ricos en fraccion fna y detritos. Las familias mas ricas fueron Cyatholaimidae y Chromadoridae, pero las halladas con mayor frecuencia fueron Xyalidae, Linhomoeidae y Cyatholaimidae. Merece destacarse que seis especies recolectadas son nuevas para la ciencia, siete son nuevos registros en aguas tunecinas y cuatro nuevos registros en la cuenca mediterranea. Este estudio aporta asimismo informacion importante para la biogeografia del flo puesto que hasta ahora algunas de las especies registradas aqui eran conocidas unicamente en otras regiones geografcas. Entre las especies que en este momento aparecen como endemicas en el mar Mediterraneo se encuentran Chromadorina metulata, Synonchiella edax, Paralongicyatholaimus mastigodes, Trichotheristus setifer yMetalinhomoeus numidicus. MultipleS’ha fet un inventari detallat dels nematodes de vida lliure de la part nord de Tunisia, pero la part sud del pais esta inexplorada. La llacuna del Bibane es la segona mes extensa de Tunisia, per la qual cosa te una importancia fonamental per al desenvolupament de futures accions de conservacio i cal avaluar–ne la biodiversitat. S’hi van trobar 71 especies de nematodes, pertanyents a 68 generes i 22 families. La riquesa mes baixa es va registrar a la zona central de la llacuna, on es concentren els percentatges mes elevats de llot i materia organica. El nombre d’especies trobades en aquest estudi es alt si es compara amb el d’altres entorns de transicio de la conca mediterrania, pero mes baix que els registrats al nord d’Europa. La major part de les especies son tipiques d’entorns de transicio o de sediments rics en fraccio fna i detrits. Les families mes riques van ser Cyatholaimidae i Chromadoridae, pero les trobades amb mes frequencia van ser Xyalidae, Linhomoeidae i Cyatholaimidae. Cal posar en relleu que sis especies recol·lectades son noves per a la ciencia, set son nous registres en aigues tunisenques i quatre nous registres a la conca mediterrania. Aquest estudi tambe aporta informacio important per a la biogeografa del filum ates que fns ara algunes de les especies registrades aqui nomes eren conegudes en altres regions geografques. Entre les especies que en aquest moment apareixen com a endemiques al mar Mediterrani es troben Chromadorina metulata, Synonchiella edax, Paralongicyatholaimus mastigodes, Trichotheristus setifer i Metalinhomoeus numidicus. EnglishA detailed inventory of the free–living nematodes of Tunisia has been made for the northern part of Tunisia, but the southern part of the country is unexplored. El Bibane is the second largest lagoon in Tunisia. It is thus of high importance for future conservation actions, but little is known about its biodiversity. In this study, we identifed 71 nematode species, belonging to 68 genera and 22 families. Richness was lowest in the central area of the lagoon where the highest percentages of mud and organic matter were found. The number of species detected in this study is high compared to other transitional environments in the Mediterranean basin, but lower than those reported for North Europe. Most of the species are typical of transitional environments or sediments rich in the fne fraction and detritus. The richest families were Cyatholaimidae and Chromadoridae, but the most frequently found species were Xyalidae, Linhomoeidae and Cyatholaimidae. Six of the species collected are new to science, seven are new records for Tunisian waters, and four are new for the Mediterranean basin. This study adds also important information to the biogeography of the phylum because some of the species detected here were previously known only for other geographical regions. Species that currently appear endemic to the Mediterranean Sea include Chromadorina metulata, Synonchiella edax, Paralongicyatholaimus mastigodes, Trichotheristus setifer and Metalinhomoeus numidicus.


Introduction
Biodiversity studies help to understand the functioning of the ecosystem and to protect natural resources (e.g.Cardinale et al., 2006;Chen et al., 2017).As awareness of the importance of oceanic biodiversity on a planetary scale has increased, so has scientific interest in understanding and estimating species richness of all components of the ecosystem, including the most inconspicuous species, such as free-living nematodes (Balvanera et al., 2006).
Nematodes are arguably the most successful metazoans on earth (Da Rocha et al., 2006;Appeltans et al., 2012).They are also key organisms in marine ecosystems and play a central role in trophic chains (Semprucci et al., 2016).They can enhance energy flow, rates of mineralization, and recirculation of nutrients, becoming an important and direct contributor to the functioning of coastal shallow ecosystems (Semprucci and Balsamo, 2012).
The aim of faunistic and taxonomical studies is to develop accurate baseline information on species biodiversity that can be used to determine if and how the ecosystem is changing (Appeltans et al., 2012).Researchers are also using these organisms as biological indicators to assess water quality and to monitor marine ecosystems (Semprucci et al., 2017).
Estimating the diversity of nematodes is particularly important in tropical and subtropical areas because studies in these areas are often scarce (Semprucci and Balsamo, 2014), thus limiting our knowledge about the biogeography of the Phylum (Liu, 2009).Although the African continent has a great heterogeneity of habitats, biogeographic sectors (e.g.Mediterranean Sea and Red Seas, Atlantic and Indian Oceans) and climatic conditions (i.e.North-South and East-West transects), information on the distribution of free-living marine nematodes is limited (Boufahja et al., 2015).According with these authors Tunisia (Northern African coast) is the area for which the most information on nematodes has been collected, followed by eastern Africa (data were mainly at genus level), while such information for southern and western Africa is practically nonexistent.Boufahja et al. (2014) published the first list of nematode species for Tunisia.They documented 419 species for the Northern Tunisian coasts, but only 95 species in the south of the country for which only Bou Ghrara lagoon has been studied.
Although El Bibane is the second largest lagoon in Tunisia and offers a wide variety of natural habitats for benthic populations (e.g.Cymodocea nodosa, Posidonia oceanica and Caulerpa prolifera, Neogoniolithion notarsii), data available are scarce (Jouili et al., 2017).Furthermore, the anthropogenic impact in this area (BRL Ingenierie Idea Consult, 2008) has increased.The aim of the present paper was to provide a preliminary list of nematode species in the El Bibane lagoon and to increase the information available on the distribution of the Phylum.
In the laboratory, the samples were washed through 1 mm and 40 μm sieves and the fractions retained by the 40 μm sieve were centrifuged with Ludox-HS40 (Mirto and Danovaro, 2004).After counting of the meiobenthic groups, we randomly picked one hundred nematodes from each sample and mounted specimens on permanent slides for taxonomical identification (Seinhorst, 1959).Genus level was identified using the pictorial keys of Platt andWarwick (1983, 1988) and Warwick et al. (1998), the NeMys online identification key, and literature therein (Guilini et al., 2017).The list of nematode species reported below is according to Hodda (2011) for the taxonomic status and NeMys website for the relative geographical distribution.The distribution of the Tunisian nematode species is reported according to Boufahja et al. (2014).All the nematode specimens found in this study were deposited in the collection of the Laboratory of Environment Biomonitoring, University of Carthage, Faculty of Sciences of Bizerte (Tunisia).
The richest families were Cyatholaimidae and Chromadoridae (9 species each), followed by Xyalidae (7), Comesomatidae (6), Desmodoridae, Linhomoeidae and Oncholaimidae (5 each).Monhysteridae and Selachinematidae were represented by three species each, while Oxystominidae, Thoracostomopsidae, Microlaimidae, Monoposthiidae and Axonolaimidae by two species each.For the other families counted, we found only one species each.It is of note that six new species (pending formal taxonomical description) were found.
The list of the species identified is given below along with their distribution in the world and in Tunisia.Some ecological information about the sampling stations is also included.The new species pending taxonomical description are not included in this list.Additional ecological notes: the species was found in seven stations in the south western part of the lagoon (Sts. 4,.It was found in sediments with a fine fraction from 8 % (St.13) to 29 % (St.4) and a level of organic matter (TOM) that ranged from 0.58 % to 2.32 %.
Distribution in Tunisia: Bizerte bay and lagoon.Additional ecological notes: the species was found in 11 stations, all in the marginal area (Sts.1-6, 10-13, 15).It was in sediments with a mud fraction from 8 % (St.13) to 29 % (St.4) and a level of TOM that ranged from 0.55 % to 2.32 %.
Distribution in Tunisia: Bizerte bay.Additional ecological notes: this species was found in all 15 stations of the lagoon.The sediments ranged from 8 % to 87 % of fine fraction and a level of organic matter that ranged from 0.55 % to 5.05 %.
Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara and Ghar El Melh lagoons.
Additional ecological notes: it was documented in eight stations located in both margins of El Bibane (Sts.1-3, 6, 9-11, 15).The species was found in sediments characterized by a range of mud from 14 % to 73 % and a level of organic matter from 0.55 % to 3.95 %.
Distribution in Tunisia: Bizerte bay and lagoon.Additional ecological notes: the species was found in only one station, which was near the Boujmel sebkhat (St.6) and characterized by 28 % of mud and 1.77 % of TOM.
Distribution in Tunisia: Ghar El Melh lagoon.Additional ecological notes: the species was found in only one station, situated close to the lagoon opening to the sea (St.2) and characterized by 14 % of mud and 0.87 % of TOM.
Distribution in Tunisia: Bizerte, Bou Ghrara and Ghar El Melh lagoons.Additional ecological notes: the species was found in only two stations in the Southern part of the lagoon (Sts. 11,12).The sediments showed a mud fraction of 12 % and 19 % and TOM of 1.84 % to 2.32 %, respectively.
Distribution in Tunisia: Bou Gharara lagoon.Additional ecological notes: the species was found in a total of 12 stations from the area located near sea to the central area to the south western part of the lagoon (Sts.1-5, 7-9, 12-15).The sediments were characterized by a fine fraction that ranged from 8 % to 87 % and a level of TOM from 0.55 % to 5.05 %.
Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara, Ghar El Meh lagoons, Northern Lake of Tunis, Old Harbour of Bizerte, southern Lake of Tunis.
Additional ecological notes: the species was found in four stations all located in the marginal area near the sea (Sts.1-4).The fine fraction of the sediments ranged from 14 % to 29 %, while TOM ranged from 0.55 % to 1.06 %.Stekhoven, 1942 Documented distribution: Mediterranean Sea, North Atlantic Ocean, North Sea, Black Sea (Ürkmez et al., 2016).

Oncholaimellus mediterraneus
Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara and Ghar El Melh lagoons, Southern Lake of Tunis, Old harbour of Bizerte.
Additional ecological notes: it was detected at two stations (Sts. 1, 4) located in the marginal area near the sea, with a fine fraction of 15 % and 29 % and TOM of 0.55 % to 0.87 %, respectively.
Additional ecological notes: it was documented in only one station (St. 1) in the extreme southern part of the lagoon.It was characterized by 15 % of mud and 0.55 % of TOM.
Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara, Ghar El Melh lagoons, Northern Lake of Tunis.
Additional ecological notes: the species was found in the throughout the El Bibane lagoon (15 stations).It was found in sediments characterized by a range of mud from 8 % to 87 % and TOM of 0.55 % to 5.05 % Order Chromadorida Chitwood, 1933Family Chromadoridae Filipjev, 1917 Chromadora brevipapillata Micoletzky, 1924 Documented distribution: Japan, Mediterranean Sea, North Atlantic Ocean.
Distribution in Tunisia: Bizerte bay.Additional ecological notes: this species was found in only two stations (Sts. 1, 2) and located in the southern part of the margin close to the sea.It was mainly found in sediments characterized by a low level of fine fraction (14-15 %) and TOM (0.55-0.87 %).Aissa & Vitiello, 1977 Documented distribution: Mediterranean Sea.Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara and Ghar El Melh lagoons, northern and southern Lakes of Tunis.

Chromadorina metulata
Additional ecological notes: this species was found only in one station, near the Boujmel sebkhat.It was found mainly in sediments with 28 % of mud and 1.77 % of TOM.
Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara and Ghar El Melh lagoons.Additional ecological notes: found only in St. 2, St. 10, and St. 11.One station was in front of the lagoon opening to the sea; the two other stations were in the southern marginal area.It was found in sediments with mud from 14 % to 19 % and TOM from 0.58 % to 1.84 %.Filipjev, 1918 Documented distribution: Mediterranean Sea, North Atlantic Ocean, Black Sea, North Sea.Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara and Ghar El Melh lagoons; and Old Harbour of Bizerte.

Neochromadora poecilosomoides
Additional ecological notes: it was found only in one station, near the Boujmel sebkhat.It was characterized by 28 % mud and 1.77 % TOM.
Distribution in Tunisia: a new record for Tunisia.Additional ecological notes: this species was found only in the station near the Boujmel sebkhat.It was characterized by 28 % of mud and 1.77 % of TOM.
Distribution in Tunisia: Bou Ghrara, Ghar El Melh, Bizerte lagoons, Northern Lake of Tunis, Old Harbour of Bizerte, Southern Lake of Tunis.
Additional ecological notes: the species was found at St. 6 (close to the Boujmel sebkhat) and at St. 13 in the western margin of the lagoon.The stations were characterized by 28 % and 8 % of mud and 1.77 % and 1.92 % of TOM.Jouili et al. Order Monhysterida Filipjev, 1929Family Axonolaimidae De Coninck & Stekhoven, 1933Odontophora villoti Luc & De Coninck, 1959 Documented distribution: North Atlantic Ocean, North Sea.Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara and Ghar El Mehl lagoons, Old Harbour of Bizerte.
Additional ecological notes: the species was found in six stations, all located on the margins of the lagoon 12,13).Mud ranged in the sediments of the stations from 8 % to 29 % and TOM from 0.67 % to 2.32 %.
Distribution in Tunisia: Bizerte lagoon.
Distribution in Tunisia: Bizerte lagoon and bay, Bou Ghrara and Ghar El Melh lagoons and Southern Lake of Tunis.
Additional ecological notes: it was collected in six stations from the area located near the margin facing the sea (Sts.1-5) and at St. 6 close to the Boujmel sebkhat.It was found in sediments with a mud fraction from 14 % to 29 % and TOM from 0.55 % to 2.01 %.
Distribution in Tunisia: the first record for Tunisia.
Additional ecological notes: it was collected only at St. 15, in 18% of mud and 1.53 % of TOM.
Distribution in Tunisia: Bizerte, Bou Ghrara and Ghar El Melh lagoons, Ichkeul Lake, Old harbour of Bizerte and Southern Lake of Tunis.
Additional ecological notes: it was collected from 13 stations both in the margins and in the central part of the lagoon (Sts.1-13).It was found in sediments with a mud fraction from 8 % to 87 % and TOM from 0.55 % to 5.05 %.
Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara and Ghar El Melh lagoons and Southern Lake of Tunis.
Additional ecological notes: it was collected in six stations from the margin facing the sea and in the station close to the Boujmel sebkhat (Sts.1-6).It was in sediments from 14 % to 29 % of mud and from 0.55 % to 2.01 % of TOM.
Additional ecological notes: it was found only in the two stations (Sts.5, 6) closest to the Boujmel sebkhat.It was mainly associated with sediments with 28 % of mud and 2.01 % and 1.77% of TOM, respectively.Aissa & Vitiello, 1977 Documented distribution: It was found only in Tunisia.

Metalinhomoeus numidicus
Distribution in Tunisia: Bizerte, Bou Ghrara and Ghar El Melh lagoons and Northern and Southern Lake of Tunis.
Additional ecological notes: it was found in all the stations (14 stations) except St. 4. It was detected in a mud fraction of 8 % to 87 % and TOM of 0.55 % to 5.05 %.
Terschellingia communis de Man, 1888 Documented distribution: Mediterranean Sea, North Atlantic Ocean and North Sea.
Distribution in Tunisia: Bizerte, Bou Ghrara and Ghar El Melh lagoons, Old Harbour of Bizerte and Southern Lake of Tunis.
Terschellingia longicaudata de Man, 1907 Documented distribution: Mediterranean Sea, Baltic Sea, Barents Sea, Gulf of Mexico, Black Sea, North Atlantic Ocean, North Sea and New Zealand.
Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara and Ghar El Melh lagoons, Ichkeul Lake, Old Harbour of Bizerte, Northern and Southern lakes of Tunis.
Additional ecological notes: it was present in eight stations located both in the central area and in the margin of the lagoon close to the sea 8,9).The species was found in sediments with ranges of mud from 14 % to 86 % and TOM from 0.55 % to 3.95 %.
Distribution in Tunisia: it is a new record for Tunisia.
Additional ecological notes: it was found only in St. 1, with a mud fraction of 15 % and TOM of 0.55 %.
Distribution in Tunisia: Bou Ghrara and Ghar El Melh lagoons and Southern Lake of Tunis.
Additional ecological notes: it was found only in a total of two stations (Sts. 5,6).The species was associated with mud values of 28 % and TOM of 2.01 % and 1.77 %.Cobb, 1917 Documented distribution: North America, Brazil.Distribution in Tunisia: it was found only in the Bizerte bay.

Scaptrella cincta
Additional ecological notes: it was collected in a total of four stations that are scattered in the lagoon (Sts. 1,6,10,11).The species was collected in sediments with a mud range from 15 % to 28 % and TOM from 0.55 % to 1.84 %.Additional ecological notes: it was documented only for St. 2 at the opening of the lagoon to the sea.The species was found in 14 % of mud and 0.87 % of TOM.

Discussion
The information currently available on the free-living nematodes of Tunisia is mainly focused on the northern part of this country, and the southern area is practically unexplored (Jouili et al., 2017).El Bibane is one of the largest lagoons in Tunisia.It has a high number of habitats that are of interest from a naturalistic point of view.However, as these habitats are under increasing exploitation, estimates of lagoon biodiversity are urgent (Guelorget et al., 1982;Pergent and Zaouali, 1992;Rabaoui et al., 2014;Jelassi et al., 2015).
The number of nematode species (71) detected in this survey is high compared to other transitional environments in the Mediterranean basin (e.g.Guerrini et al., 1998, Fabbrocini et al., 2005, Semprucci and Balsamo, 2015) and low compared to European transitional environments (Barnes et al., 2008;Ferrero et al., 2008).Moreover, six species in the Orders Chromadorida (two in Chromadoridae and one in Cyatholaimidae) and Monhysterida (one in each of the following families: Axonolaimidae, Diplopeltidae, Comesomatidae) are waiting for a formal taxonomical description and are considered new to science.Seven species are recorded for the first time in Tunisia (Boufahja et al., 2015) and four species (P.stygia, N. effilatus, P. faber and D. bruciei) are also new records for the Mediterranean basin.However, it is noteworthy that all of the species listed in this study are new records for the southern part of Tunisian waters.Among the species found in El Bibane, A. acuminate, E. ornata, O. campylocercoides, C. brevipapillata, N. poecilosomoides, L. longicaudatus, S. parasitifera, M. mirabilis, T. longicaudata, M. parva, T. flevensis and S. pilosa are cosmopolitan species with a widely documented geographic distribution.P. stygia, C. renaudae, R. elongata, N. effilatus are until now exclusively known for the Northern European sector, while P. supplementatis, L. undulatus, P. spirulifer for Pacific Ocean and/or Baltic Sea, N. gerlachi for the Atlantic Ocean and S. cincta for American coasts.Their discovery in Tunisian waters greatly increases the information available on the distribution and so on the biogeography of free-living nematodes.At the moment, C. metulata, S. edax, P. mastigodes, T. setifer, M. numidicus are confirmed as endemic to the Mediterranean Sea.However, the biogeo-graphy of meiofauna is often complicated due to the low number of studies on nematodes at species level and scarcity of reports with complete lists of species.
The nematode assemblage of El Bibane lagoon mainly comprises families of transitional environments (e.g.Villano & Warwick, 1995;Pallo et al., 1998;Barnes et al., 2008;Semprucci et al., 2014).Among the most frequent families found, Xyalidae, Linhomoeidae and Cyatholaimidae show representatives typical of muds rich in detritus and often characterized by anoxic conditions (e.g.Stekhoven, 1950;Heip et al., 1985;Semprucci, 2013;Sandulli et al., 2014).D. fallax, D. hirsutum, T. flevensis and T. setifer (Xyalidae) are among the widespread species in El Bibane together with E. longispiculosus, V. glabra and M. stekhoveni (Thoracostomopsidae, Oncholaimidae and Cyatholaimidae, respectively).The stations of the central part of the lagoon, which are characterized by the highest mud and organic matter percentages, show the lowest number of species according to the observations in literature (e.g.Semprucci et al., 2010;Vanaverbeke et al., 2011;Frontalini et al., 2014).In contrast, St. 6, located close to the Boujmel sebkhat, reveals the highest richness, as documented by Jouili et al. (2017) who reported that the area is characterized by a high diversity and ecological quality of the nematode assemblage.
In conclusion, this study underlines the relevance of faunistic studies in areas where such data are previously unknown and improves our knowledge on the global distribution of the nematodes and in the Mediterranean basin.The increase in such studies is particularly important for the inconspicuous metazoan taxa, collectively named 'meiofauna' because they have been neglected for a long time by marine biologists and ecologists worldwide (Semprucci, 2013).
Cobb, 1914Documented distribution: Chile, Ŏresund, Kiel Bay, Bay of Bengal, Antarctica, Arabian Sea.Distribution in Tunisia: Bizerte bay and lagoon, Bou Ghrara and Ghar El Melh lagoons.Additional ecological notes: it was well distributed in the inner margin of the lagoon (Sts.10-15) for a total of six stations.It was associated with sediments with a mud fraction from 8 % to 21 %, while TOM from 0.58 % to 2.32 %.Paramicrolaimus spirulifer Wieser, 1959 Documented distribution: Pacific Ocean, Baltic Sea.Distribution in Tunisia: Bizerte bay and lagoon; Ghar El Melh lagoon.