Detection of a population of Pseudosquillopsis cerisii (Roux, 1828) (Crustacea, Stomatopoda, Parasquillidae) in the northwestern Mediterranean

Detection of a population of Pseudosquillopsis cerisii (Roux, 1828) (Crustacea, Stomatopoda, Parasquillidae) in the northwestern Mediterranean. A population of the poorly–known stomatopod crustacean, Pseudosquillopsis cerisii, was detected in the NW Mediterranean Sea. To date, in Mediterranean waters, this species was only known from rare reports that were mainly based on the occurrence of single individuals. Analysis of the stomach contents of ��sh pr edat or s caught i n coastal trammel–net artisanal ��sheri es r eveal ed sever al i ndi vi dual s of t hi s speci es on a sandy bottom with nearby Posidonia seagrass beds in an area within the vicinity of Vilanova i la Geltrú (Catalonia). This is the ��r st r eport of t he speci es fr o m I beri an Peni nsul a wat er s.


Introduction
Stomatopods are a group of relatively large crustaceans, most of which are inhabitants of coastal waters and present mainly in warm intertropical seas (Schram et al., 2013).Only a few species are able to colonize colder waters at higher latitudes, or the deep sea.
Twelve species have so far been reported in the Mediterranean Sea (Abelló and Guerao, 2015), three of these being of lessepsian origin, i.e. anthropogenically introduced through the Suez Canal.Two species, the autochthonous Squilla mantis (Linnaeus, 1758), and the lessepsian Erugosquilla massavensis (Kossmann, 1880), have relatively large populations and are of commercial interest.The remaining species are only known from a handful of records, with the exception of Rissoides pallidus (Giesbrecht, 1910), which is often captured in trawl surveys (Abelló et al., 2002;Colloca et al., 2004).
Here we present the detection of a population of the stomatopod Pseudosquillopsis cerisii (Roux, 1828) based on the analysis of stomach contents of sh pr edat or s ( b l ack scor p i onsh, Scorpaena porcus Linnaeus, 1758 caught in coastal artisanal trammel net sheri es.

Material and methods
The study area encompassed sublittoral waters in the vicinity of the coastal town of Vilanova i la Geltrú, about 50 km southwest of Barcelona, in the northwestern Mediterranean (g. 1).
This study was part of a sheri es r esear ch pr o j ect st udyi ng t he cat ches of t he arti sana l sh i ng eet, spe ci call y using t r am m el nets .Sp ecial emph asi s w as gi ven t o a nalysing pr eda tor-prey interactions.Trammel nets were deployed in traditional sh i ng gr ounds, bet ween 41.17-41.18latitude N and 1.70-1.85E. Deployment followed the commercial sher y pr acti ce, with nets being set in the evening and collected at dawn in a ne sand ar ea and scatt er ed Posidonia oceanica meadows.Sampling took place at depths of between 10-20 m between March 2009 and April 2010.The standard 'one mile' commercial trammel net used had an 80 mm mesh inner layers, a 200 mm mesh outer layers, and vertical height of 1.6 m.
All captures (commercial and by-catch) were identied t o speci es l eve l, measur ed (t ot a l length, TL, in mm), and weighed.Gut contents of a selection of sh speci es (t ab l e 1) wer e also identied t o t he l o west possi b l e t axono m i c l eve l, and quanti ed.St om at opods f ound in the stomachs were sexed and measured (carapace length, CL, in mm).

Results
We identied si x i nd i vi dua l s of Pseudosquillopsis cerisii (g.2).They wer e r ead il y r ecognized by the shape of the rostrum and/or telson (Manning, 1977).No large signs of digestion were apparent.The collected P. cerisii specimens consisted of three adult males (CL range: 13.8-18.0mm), one juvenile, and two adult females (CL range: 4.0-15.0mm).The species was recorded in gut contents of 5 of the 314 scorpionsh ( Scorpaena porcus): the sh r anged fr o m 154 t o 246mm TL.The overall size range of the S. porcus captures was 150-311 mm TL.P. cerisii was not present in the stomach contents of the other sh speci es examined (table 1).Specimens of S. porcus were captured at depths of between 13 and 18 m (table 2).A single individual of another stomatopod species, Rissoides desmaresti, was also found in one S. porcus.

Discussion
Four species of the genus Pseudosquillopsis are known to date, three of which occur in the Pacic Ocean.P. cerisii is the only species of the genus described in the Eastern Atlantic, and is known to occur from the Gulf of Guinea to Mediterranean waters (Manning, 1977).It was r st descri bed by Roux ( 1828) fr o m speci mens co ll ect ed i n t he N W Med it err anean Sea, on t he island of Corsica and off Toulon (France).It is so far known only from very few specimens.
The present report of adult males and females, as well as of juveniles, supports the occurrence of a P. cerisii population in the study area and contributes to the knowledge on its habitat and depth range.This constitutes the westernmost record of the species for the Mediterranean, and the r st f or I beri an pen i nsu l a wat er s.
The large geographical gap between the Mediterranean populations and western African populations is of note.The known African range of P. cerisii occurs between the Gulf of Guinea and Senegal (Manning, 1977), with just one record of occurrence in the Canary Islands (Gran Canaria) (Barquín Díez and Moreno Batet, 1992).According to Manning (1977), the species of the genus Pseudosquillopsis shows biogeographically relict distributional patterns, as in the case of the genus Parasquilla.Given the apparent scarcity and low density of P. cerisii throughout its distribution area, study of its population characteristics merits attention.It would also be of interest to identify its particular microhabitat, which appears to be largely associated  (Giesbrecht, 1910;Manning, 1977; present records).The possible association of a poorly known species with important protected structural habitats, such as seagrass meadows, would increase their ecological value and relevance.The lack of digestive deterioration shown by most of the specimens collected suggests their predation occurred mainly at dawn.The presence of an additional species of stomatopod in the stomach of S. porcus and the absence of stomatopods in the gut contents of the remaining examined sh speci es capt ur ed i n t he sa me sa mp l es suggest s t hat scor p i onshes are sound predators of stomatopods.The black scorpionsh i s a l r eady kno wn t o pr ey on cr ust a ceans (Rafra-Nou i r a et a l., 2016; Co mpa i r e et a l., 2017) but so f ar not on st o mat opods.Other species of Pseudosquillopsis, such as P. lessoni in Pacic wat er s o ff Ch il e, ar e a l so known to be predated upon by perciform sh ( Var gas et a l., 1999).Ana l ysi s of t he st o mach contents of sit-and-wait opportunistic predators such as scorpionshes may pr ovi de an additional sampling tool for marine species that are difcu lt t o det ect usi ng tr ad iti ona l met hods.

Fig. 1 .
Fig. 1.Known distribution of Pseudosquillopsis cerisii in the Mediterranean Sea.The star shows the location of the study area where the new occurrences reported in the present paper were recorded.Fig. 1.Distribución conocida de Pseudosquillopsis cerisii en el mar Mediterráneo.La estrella indica el área donde se efectuaron los nuevos hallazgos registrados en este estudio.