INTRODUCTIONTop

Benthopelagic shrimps have a widespread geographic and bathymetric distribution from high latitudes in both hemispheres to intertropical waters (Crosnier and Forest 1973Crosnier A., Forest J. 1973. Les crevettes profondes de l’Atlantique oriental tropical. Faune Trop. 19: 1-409., Casanova and Judkins 1976Casanova J.P., Judkins D.C. 1976. Les crustacés décapodes pélagiques de part et d’autre de Gibraltar. Relations entre les faunes Atlantique et Méditérranéenne. CIEM CM 16: 1-6., Serejo et al. 2007Serejo C.S., Young P.S., Cardoso I.C., et al. 2007. Abundância, diversidade e zonaçao dos crustáceos no talude da costa central do Brasil (11°-22°S) coletados pelo programa REVIZEE/ Score central: Prospecção pesqueira. In: Costa P.A., Olavo G., Martins A.S. (eds) Biodiversidade da fauna marinha profunda na costa central brasileira. Rio de Janeiro, Museo Nacional, (Série Livros 24) pp. 133-162.). Many continental slope shrimps show cyclic movements associated with the photoperiod, as shown in some pasiphaeid and sergestid shrimps (Froglia and Giannini 1982Froglia C., Giannini S. 1982. Osservazioni sugli spostamenti verticali nictemerali di Sergestes arcticus Kroyer e Sergia robusta (Smith) (Crustacea, Decapoda, Sergestidae) nel Mediterraneo Occidentale. Atti del Convegno delle Unità Operative afferenti ai sottoprogetti Risorse Biologiche e Inquinamento Marino 1: 311-319., Cartes 1993aCartes J.E. 1993a. Day-night feeding by decapod crustaceans in a deep-water bottom community in the western Mediterranean. J. Mar. Biol. Assoc. U.K. 73: 795-811., Aguzzi et al. 2007Aguzzi J., Company J.B., Abelló P., et al. 2007. Ontogenetic changes in vertical migratory rhythms of benthopelagic shrimps Pasiphaea multidentata and P. sivado. Mar. Ecol. Prog. Ser. 335: 167-174.). This vertical daily migration behaviour shown by some of these species provides them with an important role in the transfer of matter and energy from the upper primary productive layers of the ocean, where these species tend to feed during the night, down to the epibenthic community of the continental slope, where they dwell during the day (Cartes 1993bCartes J.E. 1993b. Feeding habits of pasiphaeid shrimps close to the bottom on the western Mediterranean slope. Mar. Biol. 117: 459-468., Herring and Roe 1988Herring P.J., Roe H.S.J. 1988. The photoecology of pelagic oceanic decapods. Symp. Zool. Soc. Lond. 59: 263-290., Naylor 2010Naylor E. 2010 Chronobiology of marine organisms. Cambridge University Press, Cambridge, 252 pp.). Benthopelagic shrimps are thus a fundamental food item for fish, other crustaceans and cephalopods with nektobenthic habits on the continental slope and deep sea (Garrison and Link 2000Garrison L.P., Link J.S. 2000. Dietary guild structure of the fish community in the Northeast United States continental shelf ecosystem. Mar. Ecol. Prog. Ser. 202: 231-240., Fanelli and Cartes 2008Fanelli E., Cartes J.E. 2008. Spatio-temporal changes in gut contents and stable isotopes in two deep Mediterranean pandalids: influence on the reproductive cycle. Mar. Ecol. Prog. Ser. 355: 219-223.). Moreover, some of these species play an important ecological role and have potential for exploitation as commercial target species, as is the case of Pasiphaea japonica (Nanjo and Ohtomi 2009Nanjo N., Ohtomi J. 2009. Reproductive biology of Pasiphaea japonica females in Toyama Bay, central Japan. Fisheries Sci. 75: 1189-1195.). Studies of the biology and ecology of pasiphaeid shrimps have been conducted in a few regions, such as the Japan Sea (Nanjo 2007Nanjo N. 2007. Feeding habits of the glass shrimp Pasiphaea japonica in Toyama Bay of the Sea of Japan. Crust. Res. 36: 45-51., Nanjo and Ohtomi 2009Nanjo N., Ohtomi J. 2009. Reproductive biology of Pasiphaea japonica females in Toyama Bay, central Japan. Fisheries Sci. 75: 1189-1195.), the Mediterranean Sea (Orsi-Relini and Relini 1990Orsi-Relini L., Relini G. 1990. The glass shrimp Pasiphaea sivado in the food chains of the Ligurian Sea. In: Barnes M., Gibson R.N. (eds) Trophic relationships in the marine environment (Proc. 24th European Marine Biology Symposium). Aberdeen University Press, Aberdeen, pp. 334-346., Company et al. 2001Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73.), and the northeastern and southeastern Atlantic Ocean (Matthews and Pinnoi 1973Matthews J.B.L., Pinnoi S. 1973 Ecological studies on the deep-water pelagic community of Korsfjorden, western Norway. The species of Pasiphaea and Sergestes (Crustacea Decapoda) recorded in 1968 and 1969. Sarsia 52: 123-144., Gibbons et al. 1994Gibbons M.J., Macpherson E., Barangé M. 1994. Some observations on the pelagic decapod Pasiphaea semispinosa Holthuis 1951 in the Benguela upwelling system. S. Afr. J. Mar. Sci. 14: 59-67., Kensley and Schotte 2006Kensley B., Schotte M. 2006. Pelagic shrimp (Crustacea: Decapoda) from shelf and oceanic waters in the southeastern Atlantic Ocean off South Africa. Proc. Biol. Soc. Wash. 119: 384-394.).

The family Pasiphaeidae has a worldwide distribution, and over 90 species are known to date (Hayashi 1999Hayashi K.-I. 1999. Crustacea Decapoda: Revision of Pasiphaea sivado (Risso, 1816) and related species, with descriptions of one new genus and five new species (Pasiphaeidae). In: Crosnier A. (ed.) Résultats des Campagnes MURSORSTOM Volume 20. Mém. Mus. nat. Hist. nat. Paris 180: 267-302, Tavares and Cardoso 2006Tavares C.R., Cardoso I.A. 2006. Deep-sea Pasiphaeidae (Crustacea: Decapoda: Caridea) from off the Brazilian central coast between 11 degrees and 22 degrees S, collected by the Revizee Program. Zootaxa 1174: 27-39., De Grave and Fransen 2011De Grave S., Fransen C.H.J.M. 2011. Carideorum Catalogus: The recent species of the Dendrobranchiate, Stenopodidean, Procarididean and Caridean shrimps (Crustacea: Decapoda). Zool. Meded. Leiden 85: 195-588.). In the northeast Atlantic up to 18 Pasiphaeidae species are known to occur, eight of them belonging to the genus Pasiphaea (Casanova and Judkins 1977Casanova J.P., Judkins D.C. 1977. Les décapodes pélagiques en Méditerranée. Répartition et secteurs faunistiques. Rapp. Comm. Int. Mer Médit. 24: 125-127., d’Udekem d’Acoz 1999d’Udekem d’Acoz C. 1999. Inventaire et distribution des crustacés décapodes de l’Atlantique nord-oriental, de la Méditerranée et des eaux continentales adjacentes au nord de 25ºN. Patrimoines naturels (M.N.H.N./S.P.N.) 40: 1-383., Koukouras 2000Koukouras A. 2000. The pelagic shrimps (Decapoda, Natantia) of the Aegean Sea, with an account of the Mediterranean species. Crustaceana 73(7): 801-814.), but only two species of Pasiphaeidae are present in the Mediterranean Sea, namely Pasiphaea sivado (Risso, 1816) and Pasiphaea multidentata (Esmark, 1866).

Pasiphaea sivado is a benthopelagic caridean shrimp commonly captured as a by-catch by demersal trawling on the upper slope across the eastern Atlantic and the Mediterranean Sea (González-Gurriarán and Olaso 1987González-Gurriarán E., Olaso I. 1987. Cambios espaciales y temporales de los crustáceos decápodos de la plataforma continental de Galicia (NW de España). Invest. Pesq. 51: 323-341., Abelló et al. 2002Abelló P., Carbonell A., Torres P. 2002. Biogeography of epibenthic crustaceans on the shelf and upper slope off the Iberian Peninsula Mediterranean coasts: implications for the establishment of natural management areas. Sci. Mar. 66S2: 183-198.) down to a maximum depth of around 800 m (Abelló et al. 1988Abelló P., Valladares F.J. and Castellón A. 1988. Analysis of the structure of decapod crustacean assemblages off the Catalan coast (North-West Mediterranean). Mar. Biol. 89: 39-49., 2002Abelló P., Carbonell A., Torres P. 2002. Biogeography of epibenthic crustaceans on the shelf and upper slope off the Iberian Peninsula Mediterranean coasts: implications for the establishment of natural management areas. Sci. Mar. 66S2: 183-198.). Biological studies on this species have been mainly performed in the western Mediterranean, where it has been reported to reproduce continuously throughout the year, although peaking in autumn-winter, and a longevity of up to two years has been estimated (Company et al. 2001Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73., 2003Company J.B., Sardá F., Puig P., et al. 2003. Duration and timing of reproduction in decapod crustaceans of the NW Mediterranean continental margin: is there a general pattern? Mar. Ecol. Prog. Ser. 2621: 201-216.). The species has been shown to predate mainly on euphausiids, calanoid copepods, and epibenthic peracarid crustaceans (Lagardère 1972Lagardère J.P. 1972. Recherches sur l’alimentation des crevettes de la pente continentale marocaine. Téthys 3: 655-675., Cartes 1993bCartes J.E. 1993b. Feeding habits of pasiphaeid shrimps close to the bottom on the western Mediterranean slope. Mar. Biol. 117: 459-468.).

Pasiphaea multidentata inhabits benthic boundary layers on the middle and lower slope down to 2000 m depth (Cartes 1993cCartes J.E. 1993c. Deep sea decapoda fauna of the Western Mediterranean: Bathymetric distribution and biogeographic aspects. Crustaceana 65(1): 29-40., Abelló et al. 2002Abelló P., Carbonell A., Torres P. 2002. Biogeography of epibenthic crustaceans on the shelf and upper slope off the Iberian Peninsula Mediterranean coasts: implications for the establishment of natural management areas. Sci. Mar. 66S2: 183-198., Tecchio et al. 2011Tecchio S., Ramirez-Llodra E., Sardá F., et al. 2011. Biodiversity of deep-sea demersal megafauna in western and central Mediterranean basins. Sci. Mar. 75: 341-350.), with juveniles inhabiting shallower waters than adults (Company et al. 2001Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73.). It also performs vertical migrations into upper water layers during the night, mainly but not exclusively restricted to juveniles (Cartes 1993aCartes J.E. 1993a. Day-night feeding by decapod crustaceans in a deep-water bottom community in the western Mediterranean. J. Mar. Biol. Assoc. U.K. 73: 795-811., Aguzzi et al. 2007Aguzzi J., Company J.B., Abelló P., et al. 2007. Ontogenetic changes in vertical migratory rhythms of benthopelagic shrimps Pasiphaea multidentata and P. sivado. Mar. Ecol. Prog. Ser. 335: 167-174., Simão et al. 2014Simão D.S., Torres A.P., Olivar M.P., et al. 2014. Vertical and temporal distribution of pelagic decapod crustaceans over the shelf-break and middle slope in two contrasting zones around Mallorca (western Mediterranean Sea). J. Mar. Syst. 138: 139-149.). In the northwestern Mediterranean the species shows a marked seasonality in reproduction, with ovigerous females being only present from September to February, and it reaches an estimated longevity of around 3.5 years (Company et al. 2001Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73., Ramirez-Llodra et al. 2007Ramirez-Llodra E., Company J.B., Camps M., et al. 2007. Spatio-temporal variations in reproductive patterns and population structure of Pasiphaea multidentata (Decapoda: Caridea) in the Blanes canyon and adjacent margin, Northwestern Mediterranean Sea. Mar. Ecol. Evol. Perspect. 28: 470-479.). It is an active nocturnal feeder on benthopelagic crustaceans such as Gennadas elegans, P. sivado, P. multidentata, sergestid shrimps and small mesopelagic fish such as myctophids and Cyclothone spp. (Cartes 1993aCartes J.E. 1993a. Day-night feeding by decapod crustaceans in a deep-water bottom community in the western Mediterranean. J. Mar. Biol. Assoc. U.K. 73: 795-811.).

The main objectives of this paper are to analyse the main characteristics of the bathymetric and geographic distribution, population size structure and some reproduction-related characteristics of both P. sivado and P. multidentata in the western Mediterranean, as well as to relate the patterns obtained with geomorphologic and hydrographic characteristics.

MATERIALS AND METHODSTop

Study area and oceanographic context

The study area encompassed the continental shelf, upper and middle slope down to a depth of 800 m along the Iberian Peninsula Mediterranean coasts from Gibraltar in the SW to Cape Creus in the NE (Fig. 1). Overall, the continental shelf is very narrow in the Alboran Sea and Vera Gulf, south of Cape Palos, and widens to the north, reaching a maximum width of up to 70 km in the Ebro Delta-Columbretes Islands area. North of Barcelona, the continental shelf is heavily indented by several submarine canyons.

The western Mediterranean is influenced by the inflow of Atlantic water through the Strait of Gibraltar (Hopkins 1985Hopkins T.S. 1985. Physics of the sea. In: Margalef R. (ed.), Key environments: Western Mediterranean. Pergamon Press, New York, pp 100-125., Millot 2005Millot C. 2005. Circulation in the Mediterranean Sea: evidences, debates and unanswered questions. Sci. Mar. 69S1: 5-21.), where lighter Atlantic water inflows towards the Mediterranean on surface waters, and higher density Mediterranean water outflows towards the Atlantic Ocean at depth. This surface inflow of Atlantic waters generates two anticyclonic gyres between the Strait of Gibraltar and Cape Gata, and adjacent upwelling cells in the vicinity of the Strait (Vargas-Yáñez and Sabatés 2007Vargas-Yáñez M., Sabatés A. 2007. Mesoscale high-frequency variability in the Alboran Sea and its influence on fish larvae distributions. J. Mar. Syst. 68: 421-438.). The main current of inflowing Atlantic waters is directed from Cape Gata towards the North African coast, generating the Almeria-Oran front (AOF). From there the current continues its inflow along the North African coasts towards the central and eastern Mediterranean. The AOF is a strong thermohaline front confined to the upper layers of the water column and shows great seasonal and interannual variability in strength (Tintoré et al. 1988Tintoré J., La Violette P.E., Blade I., et al. 1988. A study of an intense density front in the eastern Alboran Sea: the Almeria-Oran front. J. Phys. Oceanogr. 18: 1384-1397.). The Atlantic water also flows northeastwardly, due to the detachment of anticyclonic gyres which reach the Balearic Islands and generate a second thermohaline front along the northeastern part of the archipelago, associated with the NE flowing Balearic Current (Tintoré et al. 1988Tintoré J., La Violette P.E., Blade I., et al. 1988. A study of an intense density front in the eastern Alboran Sea: the Almeria-Oran front. J. Phys. Oceanogr. 18: 1384-1397., López-Jurado et al. 2008López-Jurado J.L., Marcos M., Monserrat S. 2008. Hydrographic conditions affecting two fishing grounds of Mallorca island (Western Mediterranean): during the IDEA Project (2003–2004). J. Mar. Syst. 71: 303-315., Monserrat et al. 2008Monserrat S., López-Jurado J.L., Marcos M. 2008. A mesoscale index to describe the regional circulation around the Balearic Islands. J. Mar. Syst. 71: 413-420.). The interaction between the strong Northern Current, flowing southwestwards along the continental slope from the Gulf of Lions, and the Balearic Current in the Eivissa Channel region (between Cape La Nao and the island of Eivissa) generates a cyclonic gyre over the Balearic basin enclosing the oldest resident waters in its centre (Salat 1995Salat J. 1995. The interaction between the Catalan and Balearic currents in the southern Catalan Sea. Oceanol. Acta 18: 227-234., Sabatés et al. 2007Sabatés A., Olivar M.P., Salat J., et al. 2007. Physical and biological processes controlling the distribution of fish larvae in the NW Mediterranean. Prog. Oceanogr. 74: 355-376.).

Sampling and analysis

The material studied in the present work was obtained from the Spanish Mediterranean International Trawl Surveys (MEDITS_ES) performed in spring from 1994 to 2008. The aim of this project is to obtain density, biomass and recruitment indices of the main target species exploited by the demersal fishery throughout the European Union and adjacent Mediterranean countries, based on a common sampling protocol (Bertrand et al. 2002Bertrand J., Gil de Sola L., Papaconstantinou C., et al. 2002. The general specifications of the MEDITS surveys. Sci. Mar. 66S2: 9-17.). The Spanish surveys were performed on board the R/V Cornide de Saavedra. These cruises took place in spring, centred in the month of May, and had a mean duration of 28.9 valid workdays (range: 21-37), with an average of 4.0 hauls per day. The survey always started in the Alboran Sea and ended in the Gulf of Lions. All hauls were performed during day-time. Overall, samples were taken at depths ranging from 25 m down to 800 m based on a randomly stratified sampling design according to the FAO General Fisheries Commission for the Mediterranean (GFCM) geographic subareas and depth strata (Bertrand et al 2002Bertrand J., Gil de Sola L., Papaconstantinou C., et al. 2002. The general specifications of the MEDITS surveys. Sci. Mar. 66S2: 9-17.). Because of the large amount and spread of samples taken throughout this area and depths, in the present analysis it was possible to further subdivide the area into ten geographic sectors, established according to their geomorphology and previous biogeographic studies (Abelló et al. 2002Abelló P., Carbonell A., Torres P. 2002. Biogeography of epibenthic crustaceans on the shelf and upper slope off the Iberian Peninsula Mediterranean coasts: implications for the establishment of natural management areas. Sci. Mar. 66S2: 183-198., Rufino et al. 2005Rufino M.M., Abelló P., Yule A.B., et al. 2005. Geographic, bathymetric and inter-annual variability in the distribution of Liocarcinus depurator (Brachyura: Portunidae) along the Mediterranean coast of the Iberian Peninsula. Sci. Mar. 69: 503-518.): the western Alboran (WALB) from Gibraltar to Cape Sacratif; the eastern Alboran (EALB) from Cape Sacratif to Cape Gata; Alboran Island (ALBO); Vera Gulf (VERA) from Cape Gata to Cape Palos; Alacant (ALAC) from Cape Palos to Cape La Nao; Eivissa Island (EIVI); Valencia (VALE) from Cape La Nao to the Columbretes Islands; the Ebro Delta region (DELT) from the Columbretes Islands to Cape Salou/Tarragona; central Catalonia (CCAT) from Cape Salou/Tarragona to Barcelona, and northern Catalonia (NCAT), from Barcelona to Cape Creus. The sectors WALB to EIVI were considered to belong to the Algerian basin, while those from VALE to NCAT were considered to belong to the Catalano-Balearic basin. The sampling design also allowed finer 50 m range depth strata to be delimited.

The bottom trawl used was a GOC-73 model (Fiorentini et al. 1999Fiorentini L., Dremière P.-Y., Leonori I., et al. 1999. Efficiency of the bottom trawl used for the Mediterranean international trawl survey (MEDITS). Aquat. Living Resour. 12: 187-205.). The mouth of the net had a 3 m vertical opening allowing the capture of epibenthic and benthopelagic fish and crustaceans, and a codend stretched mesh size of 20 mm. The hauls were performed at a speed of 3 knots with a duration of one hour, except for the hauls performed shallower than 200 m, which had a duration of 30 minutes. A total of 1741 valid hauls were performed during the study period (Table 1).

Once on board, the total catch was separated by species, weighed and counted. When species abundances were too high, a random subsample in weight was taken to estimate the number of individuals, according to the programme protocol (Bertrand et al. 2002Bertrand J., Gil de Sola L., Papaconstantinou C., et al. 2002. The general specifications of the MEDITS surveys. Sci. Mar. 66S2: 9-17.). Density and biomass were then standardized by swept area to obtain the number of individuals and weight (in g) per square kilometre. The swept area was calculated taking into account the horizontal opening of the trawl, measured with Scanmar devices, and the distance from the starting point of the haul (net on the bottom) to the end of the effective haul (net off the bottom), measured from GPS latitude and longitude readings. Density, biomass and size structure were analysed in terms of bathymetric and geographic distribution of the two species. The number of samples taken within each combination of geographic sectors and depth intervals (and totals) is given in Table 2. Mean density and biomass values were calculated by averaging the obtained density values over the total number of hauls made within each combination of geographic sector and depth interval, including zero values. For both species, and for the whole study area, one-way analysis of variance was used to test for significant interannual differences in density (natural logarithmic transformation), after testing for normality of data and homogeneity of variances (Guijarro et al. 2008Guijarro B., Massutí E., Moranta J., et al. 2008. Population dynamics of the red shrimp Aristeus antennatus in the Balearic Islands (western Mediterranean): Short spatio-temporal differences and influence of environmental factors. J. Mar. Syst. 71: 385-402., 2009Guijarro B., Massutí E., Moranta J., et al. 2009. Short spatio-temporal variations in the population dynamics and biology of the deep-water rose shrimp Parapenaeus longirostris (Decapoda: Crustacea) in the western Mediterranean. Sci. Mar. 73: 183-197.). If no significant interannual differences were detected, a two-way ANOVA was then used considering geographical sectors and 100-m depth strata as factors to test for significant differences.

From 1998, all individuals, or a subsample of up to 60 individuals, of each species, P. sivado and/or P. multidentata, for each haul were sexed and measured (carapace length, CL) with an accuracy of 0.1 mm. Ovigerous females, and females with developed ovaries (oocytes being visible through the carapace) were considered as mature and noted down. Size frequency distributions (SFD), weighted by the density of the corresponding sample, were obtained for each combination of geographic sector and depth stratum. SFD based on <15 individuals per cell have not been presented in the obtained figures. Normal-distributed components were identified in SFD using the Bhattacharya method implemented in Fisat II. Mean sizes identified with this method for each depth stratum were pooled in a frequency distribution of significant components by geographic sector. This provides greater precision in the actual number of cohorts present in each geographic sector and in their average size (Abelló 1986Abelló P. 1986. Anàlisi de les poblacions de crustacis decàpodes demersals al litoral català: aspectes biològics del braquiür Liocarcinus depurator. PhD Thesis, Universitat de Barcelona, 285 pp., Yamasaki 1988Yamasaki M. 1988. The ecological study of mantis shrimp Oratosquilla oratoria (De Haan) with reference to its bio-production processes. Bull. Seikai Reg. Fish. Res. Lab. 66: 69-100., Queiroga 1993Queiroga H. 1993. An analysis of the size structure of Carcinus maenas (L.) in Canal de Mira (Ria de Aveiro, Portugal) using the probability paper method. Bios (Thessaloniki) 1: 89-106.). Size at sexual maturity by geographic sector was estimated by fitting a logistic function to the proportion of mature females by 1 mm CL size. Logistic fittings were compared among them using a generalized linear model analysis with geographical sectors as factors. A post-hoc test was used to compare size at 50% maturity (L₅₀) among sectors. Analysis was restricted to the sectors with the highest number of sampled females (WALB, EALB, ALAC, CCAT, NCAT).

Information on mean temperature and salinity on the bottom during each trawl was recorded with a CTD SBE-37 placed at the float-line of the net. Data from the 2001-2006 cruises were used to calculate mean temperature and salinity by depth stratum for each geographic sector. In order to assess the optimal temperature and salinity window for each species, the range, 25 and 75 percentiles were calculated. For each species each sample was additionally categorized as juvenile or adult depending on its mean CL: for P. sivado, samples with mean CL≤16 mm were considered as juvenile samples, and those with CL>16 mm as adult (Company et al 2001Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73., Simão 2013Simão D S. 2013. Distribution and population biology of pelagic decapod crustaceans of the western Mediterranean. Ph.D. Thesis, Universitat Politècnica de Catalunya 139 pp.); for P. multidentata, an evident size break at 20 mm CL was present in our SFD in agreement with the size at maturity observed by Company et al. (2001)Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73. (see also below, and Simão 2013Simão D S. 2013. Distribution and population biology of pelagic decapod crustaceans of the western Mediterranean. Ph.D. Thesis, Universitat Politècnica de Catalunya 139 pp.).

RESULTSTop

Pasiphaea sivado

Density and biomass

The overall depth distribution of P. sivado in the study area ranged between 141 and 765 m. Densities of P. sivado per haul ranged between 8 and 186109 ind. km^–2. No significant differences were found concerning interannual variability in densities (ANOVA, F_14,340=0.731, p=0.743). The interaction between depth and geographical sector was not significant (F_5,277=1.275, p=0.218). Two-way ANOVA showed that densities across both geographical sectors (F_5,277=4.331, p=0.001) and depth strata (F_3,277=20.400, p=0.000) differed significantly. The highest mean density values were found at depths between 250 and 500 m, i.e. within the preferential occurrence depth strata for the species (350-500 m) (Table 2). The WALB population showed the widest depth distribution range for the whole sampled Iberian coast populations. Sizeable densities were found in this sector at depths between 150 and 600 m. In the rest of sampled sectors, densities rose sharply only from 250 m downwards to around 500-600 m. Overall, the areas with highest mean density values were the WALB and the EALB and CCAT and NCAT. Eivissa also showed very high mean densities, but the relatively low sample size and the large variability in densities in this area makes it difficult to make any definitive statement about this area. Both density and biomass (Tables 2 and 3) followed a similar bathymetric and geographic pattern throughout the studied geographic area.

Size structure and size at maturity

Overall, sizes of P. sivado ranged from 9.2 to 26.1 mm CL. SFD per 100 m depth strata and geographic sector (Fig. 2A) revealed that the WALB population showed a clear size-increasing trend with depth, with juvenile individuals being restricted to the upper 100-300 m; the largest individuals were recorded in the two deepest strata (500-700 m). Populations along the Catalan coast did not show such a marked increasing trend, but rather showed a similar size structure with depth, except for the relatively high abundance of juveniles in the upper depth occurrence stratum (200-300 m).

Based on the analysis of significant normally-distributed cohorts in the several SFD by depth stratum using the Bhattacharya method, the frequency distribution of the mean sizes of the normally-distributed identified components per sector (Fig. 3) showed that most populations were structured in two main cohorts, broadly corresponding to juvenile (placed around 14 mm CL) and adult individuals (placed around 19 mm CL); the populations in the Alboran Sea also showed additional significant cohorts around 22 mm CL, which were not identified in the rest of the sampled sectors.

Geographic sectors were shown to be a significant factor for the analysis of maturity size (GLM, p<0.01) (Fig. 4). L50 ranged from 20.62 mm CL in the WALB to 22.98 mm CL in ALAC. A post-hoc test showed that L₅₀ was significantly smaller (p<0.05) in the WALB than in the other sectors studied, whereas there were no significant differences between the other sectors (Table 4).

Temperature and salinity

Throughout the study area, bottom temperatures ranged between 12.80 and 16.56°C, while salinities ranged between 37.14 and 38.54. Occurrences of P. sivado. took place at bottom temperatures between 12.98 and 13.42°C and salinities between 38.18 and 38.54. The temperature-salinity window was narrower for adults than for juveniles; in particular, adults occurred (percentiles 25-75) at temperatures between 13.17 and 13.27°C and salinities between 38.43 and 38.51, while juveniles occurred at temperatures between 13.04 and 13.28°C and salinities between 38.36 and 38.48.

Pasiphaea multidentata

Density and biomass

The overall depth distribution of P. multidentata in the study area ranged between 265 and 799 m. Density values of P. multidentata ranged between 7.5 and 3696 ind. km^–2. No significant differences in densities were found between years (ANOVA, F_14,321=1.266, p=0.227). Densities differed significantly between areas (F_6,295=7.489, p=0.000) but not between depth strata (F₃=0.5484, p=0.650). Significant interaction was detected (p=0.006). The highest mean densities were generally found deeper than 500 m in the Algerian basin (from WALB to Eivissa), whereas in the northernmost sectors the highest mean densities were found slightly shallower (400-500 m) (Table 2). Overall, the highest mean densities were found in the intermediate sectors, from the Gulf of Vera to Eivissa Channel. Densities were also high in the northernmost sectors (central and northern Catalonia), while the lowest density values were detected in the Alboran Sea. Biomass showed a slightly different pattern (Table 3), since the depth of the highest values was below 500 m in all sampled sectors (except the EALB), including those in the Balearic basin. This finding is related to the different size structure found in the two basins, with a higher occurrence of juveniles, occurring in shallower waters, in the northern sectors than in the rest of the sampled sectors (see below).

Size structure

Sizes of P. multidentata ranged between 7.7 and 47.9 mm CL. The most noteworthy feature of SFD per depth and sector (Fig. 2A) is that the occurrence of juveniles was practically restricted to the sectors of the Catalano-Balearic basin (CCAT and NCAT), where the population size structure was clearly bimodal, with the juvenile cohort ranging from 8 to 16 mm CL and adults from 24 to 32 mm CL. In these northern sectors, very few individuals with sizes around or larger than 40 mm CL were found. In contrast, in the populations from the Alboran Sea and Alacant, the sectors belonging to the Algerian basin, very few or hardly any juveniles were found. In these sectors, most of the population was comprised of adult individuals ranging between 24 and 32 mm CL, but a third, larger, cohort was also discernible at sizes of around 40 mm in most samples.

The frequency distribution of the mean sizes of the cohorts identified in the SFD by depth strata (Fig. 3) showed that most populations were structured in 2-3 main cohorts, broadly corresponding to juvenile (placed around 13-19 mm CL) and adult individuals, with two main cohorts, one around 30 mm CL and one around 38 mm CL, the latter not present in NCAT. Juvenile cohorts were only identified in the NCAT, CCAT and ALAC.

Temperature and salinity

P. multidentata occurred at bottom temperatures between 12.91°C and 13.43°C and salinities between 38.20 and 38.54. The temperature window was narrower for juveniles than for adults, while the salinity range for juveniles was slightly broader. In particular, adults occurred (percentiles 25-75) at temperatures between 13.10 and 13.25°C and salinities of 38.44 and 38.50, while juveniles occurred at temperatures between 13.25 and 13.30°C and salinities between 38.42 and 38.50.

DISCUSSIONTop

The information obtained during the studied series of trawl surveys was used to analyse the distribution patterns of density and biomass of the two species of the genus Pasiphaea present in the western Mediterranean throughout the southern and eastern coasts of the Iberian Peninsula down to depths of around 800 m. Furthermore, their population size structure was also described. While the overall depth range distribution of both P. sivado and P. multidentata found in the present study falls within the ranges described in the literature for these species (Cartes 1993cCartes J.E. 1993c. Deep sea decapoda fauna of the Western Mediterranean: Bathymetric distribution and biogeographic aspects. Crustaceana 65(1): 29-40., Koukouras et al. 2000Koukouras A., Doulgeraki S., Kitsos M.S. 2000. Notes on the vertical distribution of pelagic shrimps (Decapoda, Natantia) in the Aegean Sea. Crustaceana 73(8): 979-993., Fanelli et al. 2007Fanelli E., Colloca F., Ardizzone G. 2007. Decapod crustacean assemblages off the west coast of central Italy (western Mediterranean). Sci. Mar. 71(1): 19-28.), several patterns were studied in detail given the broad geographic range of the surveys (Bertrand et al. 2002Bertrand J., Gil de Sola L., Papaconstantinou C., et al. 2002. The general specifications of the MEDITS surveys. Sci. Mar. 66S2: 9-17.).

Most of the previously available information on distribution patterns, size structure and other population characteristics of the two species was restricted to the northernmost sampled area: the Catalan coasts (Abelló et al. 1988Abelló P., Valladares F.J. and Castellón A. 1988. Analysis of the structure of decapod crustacean assemblages off the Catalan coast (North-West Mediterranean). Mar. Biol. 89: 39-49., 2002Abelló P., Carbonell A., Torres P. 2002. Biogeography of epibenthic crustaceans on the shelf and upper slope off the Iberian Peninsula Mediterranean coasts: implications for the establishment of natural management areas. Sci. Mar. 66S2: 183-198., Cartes 1993aCartes J.E. 1993a. Day-night feeding by decapod crustaceans in a deep-water bottom community in the western Mediterranean. J. Mar. Biol. Assoc. U.K. 73: 795-811.,bCartes J.E. 1993b. Feeding habits of pasiphaeid shrimps close to the bottom on the western Mediterranean slope. Mar. Biol. 117: 459-468.,cCartes J.E. 1993c. Deep sea decapoda fauna of the Western Mediterranean: Bathymetric distribution and biogeographic aspects. Crustaceana 65(1): 29-40., Company et al. 2001Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73., 2003Company J.B., Sardá F., Puig P., et al. 2003. Duration and timing of reproduction in decapod crustaceans of the NW Mediterranean continental margin: is there a general pattern? Mar. Ecol. Prog. Ser. 2621: 201-216., Aguzzi et al. 2007Aguzzi J., Company J.B., Abelló P., et al. 2007. Ontogenetic changes in vertical migratory rhythms of benthopelagic shrimps Pasiphaea multidentata and P. sivado. Mar. Ecol. Prog. Ser. 335: 167-174., Ramirez-Llodra et al. 2007Ramirez-Llodra E., Company J.B., Camps M., et al. 2007. Spatio-temporal variations in reproductive patterns and population structure of Pasiphaea multidentata (Decapoda: Caridea) in the Blanes canyon and adjacent margin, Northwestern Mediterranean Sea. Mar. Ecol. Evol. Perspect. 28: 470-479.). Orsi-Relini and Pinca (1990)Orsi Relini L., Pinca S. 1990. Reproductive patterns of Pasiphaea sivado in the Ligurian Sea. Rapp. Comm. Int. Mer Médit. 32: 223. and Orsi-Relini and Relini (1990)Orsi-Relini L., Relini G. 1990. The glass shrimp Pasiphaea sivado in the food chains of the Ligurian Sea. In: Barnes M., Gibson R.N. (eds) Trophic relationships in the marine environment (Proc. 24th European Marine Biology Symposium). Aberdeen University Press, Aberdeen, pp. 334-346., respectively, provided information on reproduction and trophic interactions in the Ligurian Sea (NE of the western Mediterranean basin). No biological or population information are available from other areas within the distribution range of the two species. Our results have shown the occurrence of marked differences in both distribution and population characteristics between the southwestern areas of the Alboran Sea, located in the Algerian basin of the western Mediterranean, and the northeastern area, the Catalan Sea in the Catalano-Balearic basin.

Thus, the geographic distribution of densities of P. sivado has first shown a heterogeneous distribution pattern with two main nuclei: one in the Alboran Sea, especially in its western area, and one along the Catalan coasts in the northeast. Additionally, the bathymetric distribution in the WALB sector was markedly different from that in the other geographic sectors. In this area, the species occurred in both much shallower and deeper waters, reaching markedly higher densities at depths between 100 and 250 m, where it is largely absent in the remaining sectors. The bathymetric distribution of P. multidentata extended to shallower waters in the WALB sector. This pattern was especially evident in P. sivado, and is in agreement with the occurrence of temporal upwellings located along the northwesternmost region of the Alboran Sea, in the area around Malaga (Vargas-Yáñez and Sabatés 2007Vargas-Yáñez M., Sabatés A. 2007. Mesoscale high-frequency variability in the Alboran Sea and its influence on fish larvae distributions. J. Mar. Syst. 68: 421-438.). These upwellings are responsible for the occurrence of high primary production cells which have been shown to provide plankton blooms followed by high epibenthic shrimp secondary production (Fanelli and Cartes 2004Fanelli E., Cartes J.E. 2004. Feeding habits of pandalid shrimps in the Alboran Sea (SW Mediterranean): influence of biological and environmental factors. Mar. Ecol. Prog. Ser. 280: 227-238.). The occurrence of these upwelling cells close to the coast is caused by the interaction of the permanent strong eastward inflow of Atlantic water into the Mediterranean through the nearby Strait of Gibraltar. Inside the Mediterranean Sea, the inflow is influenced by the steep continental slope of the southern Iberian continental margin, and intense local westerly winds (Millot, 2005Millot C. 2005. Circulation in the Mediterranean Sea: evidences, debates and unanswered questions. Sci. Mar. 69S1: 5-21., Vargas-Yáñez and Sabatés 2007Vargas-Yáñez M., Sabatés A. 2007. Mesoscale high-frequency variability in the Alboran Sea and its influence on fish larvae distributions. J. Mar. Syst. 68: 421-438.), which contribute to offshore displacement of the surface water, allowing the inflow of deeper, cooler and nutrient-richer waters to shallower areas.

Within the sampled depth ranges, densities of P. sivado have been shown to be much higher than those of P. multidentata, in agreement with Company et al. (2001)Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73., who suggested that the greater fecundity output of P. sivado would support its higher population densities when compared with P. multidentata. Both juvenile and adult P. sivado are known to perform upward vertical migrations at night, while remaining on the bottom or close to it (epibenthic layer) during the day (Cartes 1993aCartes J.E. 1993a. Day-night feeding by decapod crustaceans in a deep-water bottom community in the western Mediterranean. J. Mar. Biol. Assoc. U.K. 73: 795-811., Aguzzi et al. 2007Aguzzi J., Company J.B., Abelló P., et al. 2007. Ontogenetic changes in vertical migratory rhythms of benthopelagic shrimps Pasiphaea multidentata and P. sivado. Mar. Ecol. Prog. Ser. 335: 167-174.). In this way they can be considered benthopelagic species. Night-time migrations into the water column have also been reported for P. multidentata, but mainly restricted to juveniles, with the apparent exception of the adults (CL>30 mm), which were assumed to perform bathymetric displacements along the seabed (Cartes 1993aCartes J.E. 1993a. Day-night feeding by decapod crustaceans in a deep-water bottom community in the western Mediterranean. J. Mar. Biol. Assoc. U.K. 73: 795-811., Cartes et al. 1993Cartes J.E., Sardà F., Company J.B., et al. 1993. Day-night migrations by deep-sea decapod crustaceans in experimental samplings in the Western Mediterranean sea. J. Exp. Mar. Biol. Ecol. 171: 63-73., Aguzzi et al. 2007Aguzzi J., Company J.B., Abelló P., et al. 2007. Ontogenetic changes in vertical migratory rhythms of benthopelagic shrimps Pasiphaea multidentata and P. sivado. Mar. Ecol. Prog. Ser. 335: 167-174.). However, recent research has shown that adult P. multidentata are also able to migrate vertically in the water column (Simão et al. 2014Simão D.S., Torres A.P., Olivar M.P., et al. 2014. Vertical and temporal distribution of pelagic decapod crustaceans over the shelf-break and middle slope in two contrasting zones around Mallorca (western Mediterranean Sea). J. Mar. Syst. 138: 139-149.). The day-time sampling schedule of the present trawl surveys would accordingly be suitable for sampling both juveniles and adults of the two species.

The relationship between mean density and percentage occurrence by depth stratum was used to delimit depth strata showing high figures of both density and occurrence, which could be assumed to be the optimal depth ranges for the species. These were clearly located between 300 and 500 m in P. sivado, and deeper than 500 m (down to the deepest sampled depth, 800 m) in P. multidentata. It must be emphasized that the sampling schedule clearly encompassed the whole bathymetric distribution range of P. sivado in the study area (Abelló et al. 1988Abelló P., Valladares F.J. and Castellón A. 1988. Analysis of the structure of decapod crustacean assemblages off the Catalan coast (North-West Mediterranean). Mar. Biol. 89: 39-49., 2002Abelló P., Carbonell A., Torres P. 2002. Biogeography of epibenthic crustaceans on the shelf and upper slope off the Iberian Peninsula Mediterranean coasts: implications for the establishment of natural management areas. Sci. Mar. 66S2: 183-198., Cartes et al. 1994Cartes J.E., Company J.B., Maynou F. 1994. Deep-water decapod crustacean communities in the Northwestern Mediterranean: influence of submarine canyons and season. Mar. Biol. 120: 221-229.), whereas in P. multidentata it did not reach the deepest distribution of the species, which has been reported to occur down to 2261 m depth (Cartes 1993cCartes J.E. 1993c. Deep sea decapoda fauna of the Western Mediterranean: Bathymetric distribution and biogeographic aspects. Crustaceana 65(1): 29-40.) in the Mediterranean.

Both species increased in size with depth, as shown in Company et al. (2001)Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73., with juveniles being found in much shallower waters than adults. In P. sivado, populations in the Alboran Sea reached larger sizes than those in the northwestern Mediterranean and in intermediate sectors. This implies that the population dynamics in these areas are different, and probably linked to the high productivity of the Alboran Sea (Fanelli and Cartes 2004Fanelli E., Cartes J.E. 2004. Feeding habits of pandalid shrimps in the Alboran Sea (SW Mediterranean): influence of biological and environmental factors. Mar. Ecol. Prog. Ser. 280: 227-238.). Recruitment in P. sivado was detected throughout the study area, in agreement with the main autumn-winter reproductive season of the species observed in the Catalan Sea (Company et al 2001Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73.), and was mainly located at depths shallower than 300-400 m. By contrast, recruitment in P. multidentata was not present in the Algerian basin sectors (Alboran Sea and Alacant regions), while it was marked in the Catalano-Balearic basin. The reproductive season in P. multidentata, from studies made in the Catalan Sea (Company et al. 2001Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73., Ramirez-Llodra et al. 2007Ramirez-Llodra E., Company J.B., Camps M., et al. 2007. Spatio-temporal variations in reproductive patterns and population structure of Pasiphaea multidentata (Decapoda: Caridea) in the Blanes canyon and adjacent margin, Northwestern Mediterranean Sea. Mar. Ecol. Evol. Perspect. 28: 470-479.), is centred in late autumn-winter. The absence of recruitment in spring in the geographic sectors belonging to the Algerian basin may imply that seasonality of reproduction in this species significantly differs between the populations inhabiting the two basins.

The analysis of the available environmental information clearly detected differences between the two species with respect to temperature and salinity on the bottom, as well as between juveniles and adults of the two species. Temperature and salinity windows (25-75 percentiles) of adults of the two species clearly overlapped, but the salinity range of P. multidentata was narrower than that of P. sivado, and much narrower than that of juveniles of the species, while the temperature range was contiguous but non-overlapping at a limiting temperature of 13.25°C. By contrast, the temperature-salinity window of P. sivado juveniles was much larger, and more widely overlapping, than that of the adults, which were associated with higher salinities. This finding clearly showed that in both species, but particularly in P. sivado, juveniles had a wider thermohaline window, indicating they are able to cope with a wider variability in temperature and salinity conditions. A close dependence on a restricted salinity range has also been shown in deep-sea and continental slope crustaceans, such as Parapenaeus antennatus and Aristeus antennatus (Guijarro et al. 2008Guijarro B., Massutí E., Moranta J., et al. 2008. Population dynamics of the red shrimp Aristeus antennatus in the Balearic Islands (western Mediterranean): Short spatio-temporal differences and influence of environmental factors. J. Mar. Syst. 71: 385-402., 2009Guijarro B., Massutí E., Moranta J., et al. 2009. Short spatio-temporal variations in the population dynamics and biology of the deep-water rose shrimp Parapenaeus longirostris (Decapoda: Crustacea) in the western Mediterranean. Sci. Mar. 73: 183-197.), while species displacements related to movements of water masses have also been found to occur at wide temporal and geographical scales (Cartes et al 2009Cartes J.E., Maynou F., Fanelli E., et al. 2009. Long-term changes in the composition and diversity of deep-slope megabenthos and trophic webs off Catalonia (western Mediterranean): Are trends related to climatic oscillations? Prog. Oceanogr. 82: 32-46., 2011Cartes J.E., Maynou F., Abelló P., et al. 2011. Long-term changes in the abundance and deepening of the deep-sea shrimp Aristaeomorpha foliacea in the Balearic Basin: relationships with hydrographic changes at the Levantine Intermediate Water. J. Mar. Syst. 88: 516-525.), linked to relatively small density changes in seawater masses.

The differential distribution pattern between juveniles and adults of both P. sivado and P. multidentata (Company et al. 2001Company J.B., Cartes J.E., Sardá F. 2001. Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata, in the north-western Mediterranean Sea. Mar. Biol. 139(1): 61-73.) could be related, as in other caridean shrimps inhabiting the continental slope (Company and Sardá 1997Company J.B., Sardá F. 1997 Reproductive patterns and population characteristics in five deep-water pandalid shrimps in the Western Mediterranean along a depth gradient (150-1100 m). Mar. Ecol. Prog. Ser. 148: 49-58., Carbonell and Abelló 1998Carbonell A., Abelló P. 1998. Distribution characteristics of pandalid shrimps (Decapoda: Caridea: Pandalidae) along the western Mediterranean Sea. J. Nat. Hist. 32: 1463-1474.), to trophic resource partitioning between the two ontogenetic phases, which would allow a lesser degree of intraspecific competition. The dietary overlap between these species has been shown to be low due to the different size spectra of their respective prey items (Cartes 1993bCartes J.E. 1993b. Feeding habits of pasiphaeid shrimps close to the bottom on the western Mediterranean slope. Mar. Biol. 117: 459-468.). Adults of P. sivado and juvenile P. multidentata share a similar body size range, and are both important food items for P. multidentata adults (Cartes 1993bCartes J.E. 1993b. Feeding habits of pasiphaeid shrimps close to the bottom on the western Mediterranean slope. Mar. Biol. 117: 459-468.). Thus, size segregation would also be helpful to avoid intraspecific predation.

The present study has shown that in both P. sivado and P. multidentata, the populations inhabiting the Alboran Sea were clearly differentiated from those in the Catalano-Balearic basin concerning their bathymetric distribution, density, maturity size, and population size structure. The populations in the intermediate Alacant sector showed more affinities with the Alboran Sea populations than with the northern populations, especially in P. multidentata, which is consistent with their general affinity for the Algerian basin.

ACKNOWLEDGEMENTSTop

We wish to thank all participants in the MEDITS_ES cruises for all help and facilities provided. We are also grateful to the comments of Drs J.E. Cartes, J.B. Company, E. Macpherson and F. Maynou throughout the preparation of this work. This piece of research was partially funded by projects Medits-Demermed-Evademed (IEO), CGL2009-12912-C03-03, DisMarGen_2009-FBBVA, and CTM2010-22218. DSS acknowledges a predoctoral studentship by AECID-MAE.

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