Isopod fauna , excluding Epicaridea , from the Strait of Gibraltar and nearby areas ( Southern Iberian Peninsula ) *

The crustacean isopods from the Iberian Peninsula have hitherto been studied solely from a taxonomic and monographic point of view on the Catalan and Balearic Islands’ coasts (Castelló, 1984, 1985, 1986a, 1986b), in Galicia (Reboreda, 1995; Reboreda and Urgorri, 1995) and recently in the Strait of Gibraltar and the Alborán Sea (RodríguezSánchez et al., in press). Arrontes (1987) studied the adaptative strategies of intertidal species in Asturias, and Arrontes and Anadón (1990a,b) studied 31 species in the same area. The remaining available data is dispersed throughout numerous studies of littoral benthic communities in the Peninsula, specifically in the Basque Country (San Vicente and Sorbe, 1993), Cantabria (López-Cotelo et al., 1982), Asturias (Lombas and Anadón, 1985; Viejo and Arrontes, 1992), Galicia (Viéitez, 1982; Penas and González, 1983; Planas, 1986; Junoy and Viéitez, 1988; Planas and Mora, 1989; Junoy and Viéitez, 1990b; Palacio et al., 1991; Pérez-Edrosa and Junoy, 1991; Pérez-Edrosa and Junoy, 1993; Palacio et al., 1993; Junoy and Viéitez, 1992; García et al., 1993; SCI. MAR., 65 (3): 221-241 SCIENTIA MARINA 2001

The Strait of Gibraltar is key to our knowledge of the isopod fauna from the Iberian Peninsula because of its privileged location between the Mediterranean Sea and the Atlantic Ocean.Previous research in the area, such as those of Camiñas (1984) and Cano and García (1987) in the Huelva estuary, Mayoral et al. (1994) in the mouth of the Piedras River (Huelva), Rodríguez and Viéitez (1992) in Punta Umbría (Huelva), and Drake et al. (1997), Rallo et al. (1987) in the Bay of Cadiz, have evidenced the presence of 21 species in the Atlantic Andalusian coasts.In recent years new species have been described in the Strait of Gibraltar (Castelló, 1997;Castelló and Carballo, 2000), which points to the fact that the isopod fauna from the area remains relatively unknown.
Even more recently, Rodríguez-Sánchez et al. (in press) studied the collection from the oceanographic campaign "Fauna I", composed of 32 samples obtained by trawling in the open sea or at considerable depths (only 14 were obtained at less than 44 m depth).The study cites 58 species, 28 of them found in the 14 samples from shallower depths.To this end, the greatest variety of communities and substrates were sampled (hard and soft bottoms, fauna associated to algae and animal organisms) in order to estimate the entire diversity of this group in the area.
The main goal of this work was to study the distribution of the isopods in the Strait of Gibraltar, and to try to define the limits of distribution for species endemic to the Mediterranean, or for Atlantic species which have not penetrated into the Mediterranean.

MATERIAL AND METHODS
Sampling was carried out from 1988 to 1992, in the area between the western limit of the Huelva province and the eastern limit of the Cadiz province (Fig. 1, Table 1).A total of 253 samples from 31 stations were collected (Table 2).Sampling on hard bottoms was done by scuba diving, and a Van Veen grab was used on soft bottoms.
The geographical distribution is given for each species, with concrete locations for the Iberian Peninsula.
The taxonomical information is outlined according to the Wägele (1991) systematic criteria.
The collection is located at the Departament of Didàctica de les Ciències Experimentals i de la Matemàtica, University of Barcelona.

RESULTS
A total of 1200 specimens were studied, belonging to 42 species, 30 genera, 16 families and 6 suborders.
Remarks.Tarifa is on the dividing line between the Mediterranean Sea and the Atlantic Ocean, so some of the specimens were collected at their western distribution limit.The individuals were sampled on Gelidium, taken between 0 and 2 m.
Remarks.Two females and a male were dissected.The operculum of the female is not as indented as in the figure by Carton (1961); it is only slightly concave.One of these specimens has somewhat inconspicuous spines on the proximal third, while the other one has two pairs of spines.However, the shape of the male first pleopod confirms that the specimens belong to this species.The specimens were collected at depths from 3 to 12 m, on Sargassum.
Remarks.The westernmost record of this species is from El Arrecifillo (Conil, Cádiz).Sampled on Halopteris, taken from 5 to12 m.
Remarks.Statocysts in the dissected manca specimen not seen.The species was collected at depths from 4 to 16 m.
Remarks.This is the dominant anthurid species from the Iberian littoral zone.It is adapted to great changes in salinity and is characteristic of estuarine and delta soft bottoms, although it has been frequently collected on photophile and sciaphile algae and Posidonia (Castelló, 1986b).In this study, it was collected at depths of 0-4 m, always in sediment.
Genus Monodanthura Wägele and Platvoet, 1982 Monodanthura maroccana Wägele and Platvoet, 1982 Diagnosis.Wägele and Platvoet (1982) Remarks.Setae on the outer margin of the uropodal exopod are plumous, giving a particular bushy appearance to this region of the body.The record from Algeciras Bay is the eastern limit of distribution for the species.It was collected in sediment, at depths of 3-10 m.
Remarks.The record from Tarifa is its western limit of distribution.The species was found at 3-27 m, on the sponge Reniera valliculata and the gorgonian Eunicella sp.

Arcturella poorei
Distribution.The only record is from the type locality in Algeciras Bay.
Remarks.This species is characterized by a waist at the end of the fourth pereonite.Collected on Sphaerococcus coronopifolius, at 9 m.Koehler, 1911 Diagnosis.Koehler (1911)

Astacilla paucisaetosa
Distribution.The only record available is from the type locality in Algeciras Bay.
Remarks.This species has a smooth but bulky dorsal surface on the fourth pereonite in its proximal section.Collected at 9 m, on Sphaerococcus coronopifolius.
Remarks.There is no data on the substratum where the specimen was collected, but we know it is a tubicolous species (Issel, 1913), living in habitats like polychaete tubes or root cavities of Posidonia (Castelló, 1986b).Collected at 6 m.
Remarks.Males are thinner and larger than females.In the Foz estuary, Junoy and Viéitez (1990a) found females up to 10 mm in size and males up to 16.2 mm.The coloration is variable due to the uneven presence of chromatophores.The species was collected at 0-1 m depth, on Cystoseira, Enteromorpha, Gracilaria, Zostera and in sediment.Bosc, 1802 Diagnosis.Bosc (1802)

Distribution. European and Mediterranean
Atlantic coasts.Recorded by Castelló (1986b) from Catalonia and the Balearic Islands.
Remarks.The specimen was collected in a sediment sample at a depth of 15 m, but this species is known to passively move about on the surface of objects or floating plant remains (Castelló, 1986b).Juveniles are sometimes found in plankton (Tattersall, 1911;Macquard-Moulin, 1969).
Remarks.According to Holdich (1970Holdich ( , 1976)), this species is restricted to the Atlantic, from Holland to northwest Africa; Mediterranean registers are erroneous and belong to other species in the genus.Although this is possible, especially if the specimens were determined from females or juveniles, Maggiore and Fresi (1984) registered this species from the gulf of Naples (male from port of Ischia).The registers from the eastern Spanish coast confirm its presence in the Mediterranean.The preferred habitat of this species are crevices and Balanus (Holdich, 1976).Nevertheless, we found it on Dictyota, at 0 m.(Lucas, 1849) Diagnosis.Lucas (1849) Distribution.European and African Atlantic littoral and Mediterranean.Registered from Catalonia and the Balearic Islands (Castelló, 1986a(Castelló, , 1986b)).
Remarks.The record from Tarifa is the southernmost limit for the species.It was collected from 1 to 2 m depth, on algae (Enteromorpha, Ulva, Codium, Gelidium, Corallina and Asparagopsis).
Remarks.The fact that Rodríguez et al. (1992) and our study mention it from the Bay of Cadiz, an area of port traffic, reinforces the idea that the species is passively transported (Forniz and Maggiore, 1985).It was collected in a sediment sample, at 0 m.
Remarks.This is a superficial species that prefers to live under stones or in beaches with shell remains (Jacobs, 1987).Castelló (1986b) indicated that in Catalonia and the Balearic Islands it was frequently found associated to the epibiotic janirid Jaera hopeana Costa, 1853, which is a highly specific relationship.It was collected at 0-1 m, on rock samples.
Distribution.European Atlantic and Mediterranean.Registered from the southern Atlantic littoral of the Iberian Peninsula (Nieto and Alberto, 1993), the Andalusian Mediterranean littoral (Rodríguez-Sánchez et al., in press) and the Balearic Islands (Schioedte and Meinert, 1881;Carus, 1885).
Remarks.Trilles (1975) indicated that this species lives as a parasite mainly on fish from the family Labridae, and to a lesser extent, on Gobiidae.In our study, the specimen was attached on Liza (Mugilidae).

Genus Eurydice Leach, 1815
Eurydice inermis Hansen, 1890 Diagnosis.Hansen (1890) Distribution.Atlantic European coasts.This is the second register for the Iberian waters and the Mediterranean, confirming the data by Rodríguez-Sánchez et al. (in press).
Remarks.The posterior margin on the telson in both specimens has 7 teeth.Collected on sediment, between 12 and 21 m.
Genus Natatolana Bruce, 1981 Natatolana gallica (Hansen, 1905) Diagnosis.Hansen (1905b) Distribution.European and African Atlantic coasts.This is the first record from the Iberian waters and the Mediterranean.
Remarks.Hansen (1905b) only indicates that the external margin on the exopod has 2 or 3 setae and provides no information on the endopod.There are 3 short and robust spines on the apex of the endopod of the uropod in our specimen, 2 on the inner margin and 4 on the outer margin, among numerous setae.On the outer margin of the exopod there are 2 spines and 1 or 2 on its apex (the second one could be a broken seta).It was collected in sediment, at 8 m.
Remarks.Although it has not been registered, this species is very abundant in Catalonia (pers.obs.).The larvae are pelagic because they are haematophagous and they live as ectoparasites on fish.All the specimens in our study were adults and collected at 3 -12 m in sediment and on Ircinia.
Distribution.This is the characteristic species of the Atlantic peninsular supralittoral.Vandel (1960) provides a distribution map covering the entire Atlantic peninsular littoral.Arrontes and Anadón (1990b) registered it from Asturias and Drake et al. (1997) from Cadiz Bay.
Remarks.Vandel (1960) circumscribes this species to the European Atlantic littoral zone, from Norway to the Moroccan Atlantic, and indicates that the records from Gibraltar and Malaga are incorrect.In our study, it is registered from Tarifa, the southern limit of the European Atlantic.In the southern Atlantic littoral of the Iberian Peninsula there is another species from this genus Ligia italica Fabricius, 1798, which has a fundamentally Mediterranean distribution.The two species are different in body shape, which is more robust in Ligia oceanica (Linnaeus, 1767), and in the number of articles on the antennal flagellum (11-14 in L. oceanica and 20-22 in L.italica).
Remarks.Although some authors agree that sand grain size does not condition the habitat of other species from this genus (Hayes, 1977;Kensley, 1974), Mead (1969) states that T. europaeus Arcangeli, 1938 is interstitial in fine sand beach, making its habitat different from that of T. sardous Arcangeli, 1938, which prefers coarse sand substrates.

DISCUSSION
The isopod fauna in the studied area is moderately rich (42 species, from 30 genera, 16 families, and 6 suborders), with a diversity comparable to the Galician littoral zone (39 species: Reboreda, 1995; Reboreda and Urgorri, 1995), and slightly higher than the areas of Asturias (31 species: Arrontes and Anadón, 1990a,b) and Catalonia and the Balearic Islands (32 species : Castelló, 1986b).The results by Rodríguez-Sánchez et al. (in press) point to 58 species captured at depths between 12 and 860 m; we found only 28 of them in samples from less than 44 m.Table 2 indicates that sampling was most intense between 0 and 12 m (89.3% of total samples), so the number of samples captured at this interval is proportionately larger than the rest.The same occurs with the number of species.
Regarding substrate preferences (Table 2), 16 species were found in sediment, and Cyathura carinata was characteristic of this type of habitat, as found by Sola and Arzubialde (1993) in the Bidasoa estuary (Bay of Biscay).The dominant algae substrata were Halopteris (9 species collected on it; Synisoma nadejda and Cymodoce truncata were dominant), Asparagopsis (9 species; most characteristic was Ischyromene lacazei), and Cystoseira (6 species; Idotea chelipes and Dynamene magnitorata were most abundant).Idotea chelipes and Lekanesphaera levii were found on Zostera.Some species were registered as epibiotic on other animal species, especially sponges; in this sense, Janira maculosa, Dynamene magnitorata and Gnathia maxillaris were found on Ircinia, and Stellanthura cryptobia was found on Reniera and Eunicella.Cymodoce rubropunctata and Cymodoce tattersalli were also found on Microcosmus.By taxonomic group, the Asellota prefer algae substrates, except for Janira maculosa, which is also epibiotic on other organisms.The Anthuridea species were found exclusively on soft bottoms, except for the two Paranthura species (P.costana was captured on a sample of Halopteris, and P. nigropunctata was found on a great variety of algae substrates).The Valvifera are typical of algae communities, especially on Sphaerococcus or Halopteris.There were 3 genera of Sphaeromatidea (Cymodoce, Dynamene, Ischyromene) clearly related to this same habitat, while the other 4 genera (Lekanesphaera, Paracerceis, Paradella, Sphaeroma) prefer sedimentary bottoms.Within the Cymothoida, both the Cirolanidae and the adult Gnathiidae also show a preference for this habitat.The few samples of Oniscidea were collected at their usual habitat (Ligia oceanica in small caves and Tylos europaeus in marsh sediment).
On the other hand, regarding bathymetry (Table 2), 18 species were found at 0 m.One of them (Ligia oceanica) is characteristic of the supralittoral floor and the other 17 species are from the mid-littoral floor, with Dynamene edwardsi and Ischyromene lacazei as most dominant.In the infralittoral, 33 species were found at 1-10 m, mostly Janira maculosa, Dynamene magnitorata, Cymodoce truncata, Ischyromene lacazei and Cyathura carinata; 13 species were found at a level of 11-20 m, mostly Janira maculosa.Finally, 6 species were present at 21-28 m, with Janira maculosa also most dominant.
Regarding bathymetric distribution, the Asellota species were not found below 12 m, except for Janira maculosa found near the sampling depth limit (27 m).Most of the Anthuridea were collected between 0 and 5 m, although some like Stellanthura cryptobia and Paranthura nigropunctata were also found as deep as 27 m.The Valvifera species were generally collected between 3 and 15 m, except for Idotea chelipes (0-1 m) and Arcturella damnoniensis (28 m).Synisoma nadejda was found mostly between 0 and 14 m.The Sphaeromatidea species are typically intertidal and infralittoral, but some reach greater depths (Cymodoce rubropunctata, up to 22 m, C. tattersalli, up to 16 m, and C. truncata, up to 20 m).The Cymothoida were captured at depths between 1 and 21 m, and the species found at the greatest depth was Eurydice inermis.The Oniscidea are typical of the supralittoral and intertidal zone.
From a biogeographical point of view the Strait of Gibraltar is a transit area for species.In this sense, it is important to note that Munna fabricii, Monodanthura maroccana, Campecopea hirsuta and Natatolana gallica were registered during our study in the Mediterranean for the first time (Table 3), when their distribution was heretofore restricted to the Atlantic.On the contrary, Synisoma nadejda and Uromunna petiti were registered for the first time on the Atlantic littoral.Some species were registered for the first time from the Iberian waters: Munna fabricii, Uromunna petiti, Monodanthura maroccana, Stellanthura cryptobia and Natatolana gallica (Table 3).Species new to science were described from samples in this collection, such as Arcturella poorei (Castelló, 1997), Astacilla cingulata and Astacilla paucisaetosa (Castelló and Carballo, 2000), thus constituting the first records for the Iberian fauna, the first one from the Atlantic littoral and the other two from the Mediterranean.
Perhaps because it has been sampled more intensively the location with the greatest species diversity (16; Dynamene edwardsi and Ischyromene lacazei are heavily dominant) is Tarifa (station 14), which can be considered a boundary between the Atlantic Ocean and the Mediterranean Sea.Some species from this location include Joeropsis brevicornis, Stenetrium mediterraneum, and Stellanthura cryptobia, with a Mediterranean distribution, thus they probably are already introduced in the Atlantic Ocean.Conversely, Ligia oceanica was also found here, a species from the Atlantic littoral (Table 3).Paradella dianae and Paracerceis sculpta, already registered from the Mediterranean and the Straits of Gibraltar, were registered in this study from the Bays of Algeciras and Cadiz, respectively, which are areas of heavy port traffic, and the presence of those species is thus explained as they are passively transported on ship hulls (Rodríguez et al., 1992).
It is currently well established that the connection between the Mediterranean and the Atlantic was interrupted as a consequence of the Euroasian and African plates coming together at the end of the Miocene, approximately 8 or 9 million years ago (Maldonado, 1989).The Mediterranean was subsequently transformed into a series of great lakes, into which great quantities of salts precipitated, thus extinguishing practically all the marine benthic species, except possibly for those that remained in those small areas that received water from rivers.This period is known as the "Messinian salinity crisis", which ended about 5 million years ago with the opening of the Straits of Gibraltar and the consequent flow of Atlantic waters that filled the Mediterranean, at the beginning of the Pliocene (Pérès, 1989).The Straits of Gibraltar is a very important geographic-geological formation which separates the Atlantic from the Mediter-ranean.It is located between very different marine environments and constitutes an extremely interesting faunistic enclave due to its special location between the Mediterranean Sea and the Atlantic Ocean.Study of its marine fauna can help define the limits of distribution for species endemic to the Mediterranean, or for Atlantic species which have not penetrated into the Mediterranean as has been demonstrated with others important benthic groups such as sponges (Carballo et al., 1996) or ascidians (Naranjo et al., 1998).The present study is a new contribution to this knowledge.

TABLE 1 .
-List of sampling stations and geographical location.
Rodríguez-Sánchez et al. (in press) from both sides of the Strait of Gibraltar.

TABLE 2 .
-Material examined showing the sampling data.