Checklist of free–living nematode species in the transitional environment of Lake Varano (Southern Italy)

Checklist of free–living nematode species in the transitional environment of Lake Varano (Southern Italy).— This study documents �or the first time the taxonomic composition o� the nematode community and the number o� �ree–living nematode species in La�e Varano, Southern Adriatic Sea, Italy. The nematode community was mainly composed o� species typical o� fine sediments that usually prevail in transitional environments (TEs). An overall high number o� nematode species was recorded (55), belonging to 36 genera in 17 �amilies. These values are highly comparable to those reported �or other Italian TEs, but appear lower than those recorded in other European brac�ish–water systems, probably in relation to the low salinity range o� La�e Varano. Forty taxa were identified up to species level, thus increasing the number o� the nematode marine species �nown �or the Italian coasts �rom 443 to 463, �or the Adriatic basin �rom 310 to 313, and �or the Southern Adriatic sector �rom 37 to 77. Considering the impor� tance o� this phylum in the assessment o� ecological quality and the great vulnerability o� the Adriatic Sea ecosystems, an intensification o� sampling e��orts should be planned, especially in the Central–Southern part o� the basin. Such a plan would provide new insights into the biogeography o� one o� the most important components o� the benthic domain and potentially yield new in�ormation about the climate warming e��ects on the Adriatic Sea. Data published through GBIF [doi:10.15470/x�tjni]


Introduction
Transitional environments (TEs) are aquatic systems characterized by large fluctuations o� physicochemical and geochemical variables that could greatly a��ect the benthos (Barnes et al., 2008;. The Adriatic Sea coast, in particular, hosts a large amount o� TEs, ranging �rom the largest and most studied Lagoon o� Venice to wetlands, estuaries, embayments and ponds. All these habitats have been modified to meet human requirements �or millennia and are currently under severe stress due to anthropogenic activities and climate change (Airoldi & Bec�, 2007).
The species o� marine nematodes �nown in the Italian seas are 443 and are distributed into 262 genera and 46 �amilies (Semprucci et al., 2008). Since the total number o� Ital� �amilies (Semprucci et al., 2008). Since the total number o� Ital� Since the total number o� Ital� ian species is a quarter o� that o� species recorded along European coasts, the overall level o� �nowledge �or the Italian Seas can be considered good. However, these data were collected in the early the 20 th century and should be updated (Semprucci, 2013). Furthermore, studies on nematode communities are scarce in southern Italy and have mainly been �ocused around genus level (De Zio, 1964, 1966Grimaldi-De Zio, 1967, 1968a, 1968bDe Leonardis et al., 2008;Sandulli et al., 2010Sandulli et al., , 2011. This is also true �or the only in�ormation available on the nematodes o� the Lesina Lagoon, a southern Italian TE (Fabbrocini et al., 2005).
La�e Varano is a coastal lagoon located on the northern side o� the Gargano National Par� (Southern Adriatic Sea). It comprises an area o� about 65 �m 2 and its water depth is about 4 m (Spagnoli et al., 2002). The la�e is �ed by two artificial channels (Capoiale and Varano) connecting it with the Adriatic Sea and by two tributaries (Antonino and San Francesco Canals) bringing �resh waters �rom the catchment area. However, the range o� salinity range in La�e Varano is generally low (�rom 23.0 to 31.9) (Frontalini et al., 2013).
In this paper, we list the species and their distribution both at a global and local scale. We also discuss the state o� �nowledge o� Nematoda �rom the Adriatic basin and southern Italy along with the TE.

Material and methods
Sediment samples �rom 21 stations were collected on 22nd March 2012 using a modified model o� Van Veen Grab ( fig. 1). Samples were treated with a 7% MgCl 2 aqueous solution to narcotize the �auna, fixed in a 4% �ormaldehyde solution in bu��ered sea-water, and stained with Rose Bengal. In the laboratory, the samples were rinsed with a gentle jet o� �resh water through a 0.5 mm sieve to remove the macro�aunal components. The residual sediment was then decanted, sieved 10 times through a 42 μm mesh and centri�uged three times with Ludox HS30 (specific density 1.18) (P�ann�uche & Thiel, 1988). One hundred nematodes were randomly pic�ed �rom each sample and mounted on permanent slides �or taxonomic study (Seinhorst, 1959). The specimens were observed under Nomars�i Di�� (Seinhorst, 1959). The specimens were observed under Nomars�i Di�� Seinhorst, 1959). The specimens were observed under Nomars�i Di�� , 1959). The specimens were observed under Nomars�i Di�� The specimens were observed under Nomars�i Di�� �erential Inter�erence Contrast illumination (Optiphot-2 Ni�on, 100x oil immersion objective) and identified by means o� the NeMys online identification �ey (Vanaverbe�e et al., 2015). The list o� nematode species reported below �ollows Hodda (2011) �or the taxonomic status and the Nemys website �or the relative geographical global distribution: in the cases �or which updates o� the latter were available specific re�erences are cited in the Results sec� tion. The distribution o� nematode species along the Italian coasts re�ers to Semprucci et al. (2008), while the recording localities in Adriatic Sea relate to Travizi & Vida�ović (1997) and Semprucci (2013). All the nematode specimens studied are deposited in the collection o� the Zoology Laboratory o� the University o� Urbino (Italy).
Fi�teen taxa were identified as putative species because the specimens collected were juveniles or �emales, which o�ten lac� the diagnostic �eatures required �or an accurate taxo� nomic identification. However, their records are shown in table 1 because they contribute to the �ew available data �or the Southern Adriatic coasts.
The list o� species identified is given below: Ecological notes: the species was �ound in the southern part o� the la�e in sediments with a prevalent �raction o� mud (mud: 66-68%; sand: 32-34%) and a level o� organic matter (CaCO 3 content) ranging �rom 34 to 44%.
Ecological notes: the species was collected in a western station o� the la�e. The sedi� ments were characterized by a prevalent amount o� mud (58%) and the CaCO 3 content was high (81%).
Ecological notes: it was �ound in �ront o� the Capoiale Channel. The sediments were sandy deposits (sand: 63%; mud: 41%) characterized by 41% o� CaCO 3 . Ste�hoven, 1942 Geographical distribution: Mediterranean Sea, North Atlantic Ocean, North Sea. Sergeeva (1977) also reported this species �rom the Blac� Sea. In Italy, it was reported �or the South Tyrrhenian Sea and the Northern Adriatic Sea: here it was recorded at Mirna Estuary, Rovinj area and Ma�ars�a harbour area (Croatia).
Ecological notes: this species was scarce in the study area. It was mainly �ound in sandy sediments and only in one case in sediments with a dominance o� mud (St. 31) (range o� sand: 16-90%; mud: 10-84%). It was generally associated with relatively high levels o� CaCO 3 (10-56%).

Chromadorella salicaniensis Boucher, 1976
Geographical distribution: North Sea and Adriatic Sea. It was �ound in the Venice Lagoon (Northern Adriatic Sea).
Ecological notes: it was not abundant in the study area and �ound only at two stations close to the baymouth bar. It was collected mainly �rom sandy sediments (sand: 73-90%; mud: 10-27%) characterized by a low level o� CaCO 3 (10-28%).
Chromadorina germanica (Bütschli, 1874) Wieser, 1954 Geographical distribution: Mediterranean Sea, North Atlantic Ocean, North Sea. In particular, it was �nown in Italy only �or the Ligurian and Northern Tyrrhenian coast.
Ecological notes: it was more �requent in the northern-central part o� the la�e. It was related to sediments characterized by a roughly equal �raction o� sand and mud (39-68% and 32-61%, respectively). The amount o� CaCO 3 was variable, ranging �rom 23 to 81%.
Neochromadora papillosa Pastor de Ward, 1985 Geographical distribution: West Atlantic. This is the first record �or the Italian coasts.
Neochromadora poecilosomoides (Filipjev, 1918) Micoletz�y, 1924 Geographical distribution: Blac� Sea, Mediterranean Sea, North Atlantic Ocean, North Sea. The previous reports in the Italian coasts were �rom the Ligurian and Southern Tyrrhenian Seas, Strait o� Messina, the south-eastern tip o� Sicily and the northern part o� the Adriatic sector (Rovinj area).
Ecological notes: it was �ound in several stations, but especially in the northern part o� the la�e and mainly in relation to the sand �raction (sand: 16-90%; mud: 10-84%). The amount o� CaCO 3 varied �rom 9.5 to 80%.
Ecological notes: it was mainly collected �rom the marginal zones o� the la�e, in sediments ranging in sand percentage �rom 16 to 73% and in mud �rom 27 to 84%. The CaCO 3 level varied �rom 10 to 81%. Filipjev, 1918 Geographical distribution: Blac� Sea, Mediterranean Sea, North Atlantic Ocean. The Adriatic sector was the only part o� the Italian coasts reported to host this species (o��shore area o� the Rovinj -Po River mouth and Poreć-Venice transects, Lim Channel, Rovinj area and Raśa Bay, Croatia).
Ecological notes: it was �ound only in �ront o� the baymouth bar, in sandy sediments (sand: 90% and mud: 10%) with a very low organic content (10% o� CaCO 3 ). Warwic�, 1971 Geographical distribution: Barents Sea, North Atlantic Ocean, North Sea. It is the first record �or Italy.
Ecological notes: it was located especially in the northern and central part o� the la�e. The sediments were mainly characterized by a dominant sandy component (�rom 39 to 90%) with a medium-low organic content (CaCO 3 �rom 10 to 63%). Coninc�, 1965Family Desmodoridae Filipjev, 1922 Desmodora granulata Vincx & Gourbault, 1989 Geographical distribution: France (Morlaix, Brittany). This is a new record �or Italy.

Molgolaimus allgeni
Ecological notes: it was detected in almost all the stations o� the study area and was one o� the most abundant species. It was mainly associated with the fine sediment �raction (sand: 32-73%; mud: 27-84%) and organic enrichment (CaCO 3 : 10-81%).
Ecological notes: it was one o� the most widespread species in the la�e, but it was especially abundant in �ront o� the two channels) and in the central parts o� the la�e. Sedi� �ront o� the two channels) and in the central parts o� the la�e. Sedi� parts o� the la�e. Sedi� ments were muddy (mud �raction �rom 37 to 84%; sand �raction �rom 16-65%) and usually contained a high level o� organic matter (CaCO 3 �rom 10 to 81%). Man, 1922(op. Kovalyev & Tchesunov, 2005 Geographical distribution: Argentina (Fuegian Archipelago), Baltic Sea, English Channel, Mediterranean Sea, North Atlantic Ocean, North Sea, South Atlantic Ocean, Southern Ocean (Antarctic Ocean, Graham Island, King George Island, South Weddell Sea), Uruguay, East Pacific.

Microlaimus honestus De
In Italy it was reported only �or the Tyrrhenian coasts. The present finding is a new record �or the Adriatic basin.
Ecological notes: this species was �ound in almost all stations, but especially in �ront o� two channels and in the central part o� the la�e. Sediments were mainly muddy (mud: 27-84%; sand: 16-73%) and salinity levels ranged �rom 23 to 30‰. Ecological notes: the species was �ound only in the area close to the baymouth bar and mainly in sandy sediments (sand: 43-90%; mud: 10-57%) with a CaCO 3 level �rom 10 to 27%.
Odontophora wieseri Luc & De Coninc�, 1959 Geographical distribution: North Atlantic Ocean. In Italy, it was previously �nown only in the Central Adriatic Sea.
Ecological notes: it was collected in �ew stations, mainly located in the northern part o� the la�e. It was strongly associated with the sandy �raction o� the sediment (sand: 42-90%; mud: 10-58%) and a low organic content (CaCO 3 : 10-81%).
Ecological notes: species abundant and widespread in the area. It was mainly related to fine sediments (mud: 35-84%; sand: 16-65%) in conjunction with levels o� salinity �rom 23 to 30‰.
Ecological notes: it was �ound in only one station at the western part o� the la�e, with 57% o� sand and 43% o� mud, and 54% o� CaCO 3 . Lorenzen, 1966 Geographical distribution: North Atlantic Ocean and North Sea. It is the first record in Italy.

Metalinhomoeus musaecauda
Ecological notes: it was �ound in a �ew stations, mainly located in the Southern part o� the la�e and in �ront o� the Capoiale Channel. It was collected �rom sediments characterized by a prevalent mud component (�rom 47 to 68%), while the sand �raction was generally lower (32-53%). The level o� CaCO 3 ranged �rom 34 to 63%. Ott, 1972 Geographical distribution: North Atlantic Ocean (North Carolina). It is the first record in Italy.

Terschellingia brevicauda
Ecological notes: it was �ound mainly in the northern and western part o� the la�e in sediments characterized by a prevalent sandy component (sand: 32-73%; mud: 27-68%) and a medium-high level o� organic content (27-63%).

Terschellingia communis De Man, 1888
Geographical distribution: Mediterranean Sea, North Atlantic Ocean and North Sea. In the Adriatic Sea, it was recorded at the o��shore area o� the Rovinj -Po River mouths and Poreć-Venice transects, Po Delta, Venice Lagoon, Mirna Estuary, Lim Channel, Rovinj area, Raśa Bay and Ma�ars�a harbour area Ecological notes: it was �ound only in the central and eastern part o� the la�e. It was mainly associated with sediments, with a sand percentage �rom 44 to 65% and mud �rom 35 to 56%. The level o� organic matter content ranged �rom 21 to 48%.

Terschellingia longicaudata De Man, 1907
Geographical distribution: Baltic Sea, Barents Sea, Gul� o� Mexico, Mediterranean Sea, North Atlantic Ocean, North Sea and New Zealand zone. Ür�mez et al. (2011) also reported its presence in the Blac� Sea. In the Adriatic Sea, it was reported in the o��shore area o� the Rovinj -Po River mouth and Poreć-Venice transects, Po Delta, Venice Lagoon, Mirna Estuary, Lim Channel, Rovinj area, Raśa Bay, Ma�ars�a harbour area and South Adriatic (eastern coasts).
Ecological notes: it was abundant and �requent in all the stations o� the la�e. It was �ound in sediments with ranges o� sand �rom 16 to 63% and mud �rom 27 to 84%. The range o� CaCO 3 was 10 to 81%.
Ecological notes: it was recorded in a single station in the central part o� the la�e, with sandy sediments (sand: 60% and mud: 40%) and a medium level o� organic matter (25% o� CaCO 3 ).

Family Monhysteridae De Man, 1876
Thalassomonhystera parva (Bastian, 1865) Jacobs, 1987 Geographical distribution: North Atlantic Ocean, North Sea. It is the first record in Italy.
Ecological notes: it was well distributed in the la�e, but more abundant in the eastern part. It was associated with sediments mainly represented by mud (32-68%) and sand (32-68%). The organic content varied �rom 10 to 81% and the species was related to salinity levels ranging �rom 23 to 29‰.

Family Sphaerolaimidae Filipjev, 1918
Sphaerolaimus gracilis De Man, 1876 Geographical distribution: Blac� Sea, Mediterranean Sea, North Atlantic Ocean and North Sea. In the Northern Adriatic sector, it was reported in the o��shore area o� the Rovinj -Po River mouth and Poreć-Venice transects and Rovinj area.
Ecological notes: it was collected �rom the stations close to Capoiale and Varano Chan� nels and in the south-eastern part (see San Antonio Canal). It was �ound in sediments with a generally high level o� mud (range �rom 37 to 84%) and low level o� sand (16 to 63%) and an organic content that ranged �rom 10 to 44% o� CaCO 3 .
Ecological notes: it was �ound in a �ew stations, mainly located in the northern part o� the la�e (Varano Channel) and at one station on the western coast. The species was associated with a prevalent mud component (mud range: 43-61%; sand range: 39-57%) and a generally high amount o� organic matter (CaCO 3 : 31-56%).
Ecological notes: it was �requent and abundant in the Varano La�e and was particularly abundant in the stations close to the San Francesco output and in the central area. It was present in sediments characterised by 27-84% o� mud and 16-73% o� sand, and appeared more abundant in sites with a low salinity level.
Ecological notes: it was collected only near the baymouth bar in relation to sandy sedi� ments (sand: 90%; mud: 10%) with a poor organic content (CaCO 3 : 10%). Timm, 1963 Geographical distribution: Arabian Sea. This is the first record in Italy.

Steineria simplex
Ecological notes: it was collected only at one station located on the eastern edge o� the la�e, in sandy sediments (sand: 65%; mud: 35%) with a high organic content (48%).
Ecological notes: this species was �ound only in the area close to the baymouth bar and in particular in sandy sediments (sand: 63%; mud: 41%) with 41% o� CaCO 3 .

Discussion
Given its particular physico-chemical �eatures, the Adriatic Sea is strongly influenced by meteorological conditions and river discharges, and it is particularly sensitive to human impact and climatic changes (Occhipinti-Ambrogi et al., 2005;Balsamo et al., 2010;Fron� talini et al., 2011).
However, the biodiversity o� the Adriatic macro�auna does not appear to have su��ered a substantial decrease during the last years, mainly because alien species have mas�ed the overall species loss, but the trophic web and the �unctioning o� marine ecosystems have been a��ected (e.g., Occhipinti-Ambrogi, 2002, 2007Giani et al., 2012).
I� it is relatively easy to document the changes in macro�aunal communities over time, it is not possible to do the same �or meio�aunal organisms since their spatial distribution is �requently understudied in many geographical regions (Balsamo et al., 2010). Even when data are available, they are o�ten outdated, ma�ing it di�ficult to determine biogeographic patterns or to support possible hypotheses o� 'tropicalization' o� the Adriatic Sea (Artois et al., 2011;Semprucci, 2013). The significance o� the present study is that it provides a de� tailed list o� nematode species �rom a littoral area o� the Southern Adriatic Sea and updates �nowledge on the Mediterranean regions.
O� the 55 species identified in the present study, 20 are new records �or the Italian coasts, three are new records �or the Adriatic basin, and 40 are reported �or the first time �or the Southern Adriatic sector (Semprucci et al., 2008). These data greatly increase our �aunistic �nowledge about the distribution o� marine Nematoda along the Italian coasts, and especially in the TE systems that are still poorly �nown environments.
The lagoon has been intensively exploited, mainly �or mussel aquaculture (Beneduce et al., 2010), but agricultural activities have also been noted to have some impact in the surrounding areas (Specchiulli et al., 2008). However, a significant anthropogenic impact on the meiobenthic communities o� the La�e Varano was not detected despite the economic development o� the surrounding area (Frontalini et al., 2014). This suggests that the com� position o� the nematode community reported in this study represents a poorly disturbed environment and could be a valuable baseline �or �uture monitoring programs (Moreno et al., 2011).