Pasiphaea Sivado Research Articles

Sexual dimorphism and associated population characteristics in the benthopelagic shrimp <em>Pasiphaea sivado</em> (Crustacea: Caridea: Pasiphaeidae)

Morphological and size dimorphism between genders of the benthopelagic shrimp Pasiphaea sivado are reported for the first time in the present work. All five pleopod protopods of females are thinner and more elongated than the male pleopod protopods, which in turn are anteriorly rounded and have robust shapes. The shape variability of the second pleopod protopods was also analysed using geometric morphometrics techniques which clearly differentiated between the thinner, elongated shape of the females and the robust shape of males. An important application of the observations of sexual dimorphism in pleopod shape in adult P. sivado is, from now on, the ability to quickly assess the gender of individuals when fisheries and population biology studies are carried out in the field unaided by a magnifying. A critical size from which the population sex ratio biases changed from female to male dominance was found in all studied western Mediterranean populations of P. sivado. This critical size different and became progressively smaller from populations in the Alboran Sea to populations in the Catalan Sea. Concerning sex ratio, no significant tendency of gender segregation was found across the bathymetric distribution range of the species, suggesting that this species does not perform differential depth distribution by gender.

Length–weight relationships for 22 crustaceans and cephalopods from the Gulf of Cadiz (SW Spain)

Life history traits are available for many fish species in different regions, but less so for invertebrates such as cephalopods and crustaceans, though, they are increasingly needed for implementing an ecosystem-based approach. Recent food web modelling in the Gulf of Cadiz has identified invertebrates as keystone groups. However, information on life history traits of such groups remains incomplete in this region. To fill this knowledge gap, we report length–weight relationships for 12 cephalopods and 10 crustaceans collected in the Gulf of Cadiz from 2009 to 2013. This study reports, for the first time, life history traits of nine species in the area (Chlorotocus crassicornis , Pasiphaea sivado , Plesionika heterocarpus , Plesionika martia , Processa canaliculata , Solenocera membranacea , Allotheutis media , Sepia orbignyana and Sepietta oweniana ). For each species, length–weight relationships, minimum and maximum lengths, mean weights, and depth ranges are presented. Overall, the results revealed that all species showed negative allometric growth (hypoallometry), except P. sivado , the only species showing an isometric growth pattern. We expect that this study will contribute to link sustainable fisheries with biodiversity conservation goals enabling the implementation of operational ecosystem-based management in the Gulf of Cadiz.

Pasiphaeid shrimps in the western Mediterranean: geographical variability in distribution and population patterns

This work aimed to analyse the main characteristics of the bathymetric and geographic distribution, population size structure and size at maturity of the continental slope caridean shrimps Pasiphaea sivado and Pasiphaea multidentata in the western Mediterranean, as well as to try to relate the patterns obtained with geomorphologic and hydrographic characteristics. The study area encompassed the Mediterranean coast of the Iberian Peninsula. In both species, marked differences in depth distribution, density, and population size structure were found between Algerian basin populations, particularly in the Alboran Sea, and those in the Catalano-Balearic basin. Both shrimps showed a shallower bathymetric range in the westernmost region of the Algerian basin than in the rest of geographic sectors, linked to the occurrence of upwelling areas on the northwestern edges of the Alboran Sea. Populations of P. sivado reached larger densities, sizes and maturity size in the Algerian basin. No recruitment of P. multidentata was detected in the Algerian basin, whereas it was present in the Catalano-Balearic basin. In both species, the window range of bottom temperature and salinity was larger in juveniles than in adults. These different distribution and population dynamics imply that ecological functioning of these species differs between the two geomorphological basins of the western Mediterranean Sea.

Trophic habits of the Ommastrephid squid Illex coindetii and Todarodes sagittatus in the northwestern Mediterranean Sea

Squids Illex coindetii and Todarodes sagittatus were collected from commercial trawls in the NW Mediterranean Sea and their stomach contents were analyzed to describe and compare their feeding habits. Fish, crustaceans and squids were found in the stomach contents of both squid species; however T. sagittatus had a wider trophic spectrum composed by fifteen prey items more than I. coindetii. This difference was attributed to the availability of feeding resources in the water column and the larger size and deeper distribution of T. sagittatus. The index of relative importance showed that the crustacean Pasiphaea multidentata was the most important prey for both squids, and that I. coindetii fed secondly on Anchilomera blossevillei, Pasiphaea sivado and the fish Lestidiops sp., while T. sagittatus fed secondly on Phronima sedentaria and the fish Arctozenus risso. The feeding habits of the two squids varied for two prey items at the size interval between 9.1 and 21cm ML. This difference was due to the presence of the amphipod P. sedentaria and the squid Ancistroteuthis lichtensteinii in the stomach contents of T. sagittatus, which are species with deeper distributions. T. sagittatus larger than 21cm ML preyed on other crustaceans and fish, such as big Pandalidae crustaceans and gadiform fish. Finally, the %FO analysis showed that there were fifteen common prey species in the feeding habits of the two squids, but they did not have the same importance for each squid. I. coindetii fed mainly on Lestidiops sp., Chauliodus sloani and P. multidentata and T. sagittatus fed on A. risso and P. sedentaria. These species correspond to mesopelagic fish, decapod crustaceans and amphipods. This suggests that these species are easy to prey at different levels in the water column, which affects the predation and distribution of I. coindetii and T. sagittatus.

Vertical and temporal distribution of pelagic decapod crustaceans over the shelf-break and middle slope in two contrasting zones around Mallorca (western Mediterranean Sea)

The pelagic decapod crustacean fauna of two different zones (Sóller and Cabrera) with different hydrographic dynamics and oligotrophy levels was studied around Mallorca (western Mediterranean), the latter with a higher degree of oligotrophy than the former. Samples were taken with a Pelagic Trawl and an IKMT in the upper 600m of the water column, targeting larger and middle-sized nektonic species, respectively. Fourteen species were collected: five dendrobranchiate shrimps, eight caridean shrimps and one scyllarid lobster. Some species were restricted to the shelf-break: Chlorotocus crassicornis and Plesionika heterocarpus. Others were exclusive of the middle slope: Pasiphaea multidentata, and Sergia robusta. Pasiphaea sivado and Gennadas elegans occurred in all pelagic strata. Multivariate analyses showed several distinct assemblages related to bathymetry and sampling depth. No significant differences were found concerning zone or sampled seasons. Bathymetrically, Deep Scattering Layers showed the highest diversity. No decapod crustaceans occurred in epipelagic daytime samples. The pelagic decapod community sampled was structured by both the geomorphology (and associated hydrographic characteristics over the shelf-break) and the influence of light in the water column. Size analysis showed species-specific patterns concerning size/age movements into the water column throughout the day–night cycle.

Spatial characterization of megabenthic epifauna of soft bottoms around mud volcanoes in the Gulf of Cádiz

The structure and composition of megabenthic epifauna from the mud volcano field known as El Laberinto and the nearby soft bottoms were analysed. Species abundance and biomass data were obtained from the Arrastre Región Sur-Atlántica bottom trawl surveys carried out routinely from 1993 to 2009. A high biodiversity of megabenthic epifauna was found with a total of 272 species. Univariate community descriptors displayed similar values in zones inside and outside El Laberinto and in different seasons with the exception of abundance, which was larger in the autumn, especially in the zone nearest the mud volcano field. The dominant species in terms of abundance in all zones were similar and included Pasiphaea sivado, Plesionika martia, Parapenaeus longirostris, Nezumia aequalis, Chimaera monstrosa, Galeus melastomus and Etmopterus spinax. This information could be useful for increasing knowledge on biodiversity and the occurrence of commercial species and for establishing conservation strategies for protection of mud volcanoes within El Laberinto, and also including the surrounding seafloor to reduce the impact of trawl fisheries within the mud volcano field.

Ontogenetic changes in vertical migratory rhythms of benthopelagic shrimps Pasiphaea multidentata and P. sivado

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 335:167-174 (2007) - doi:10.3354/meps335167 Ontogenetic changes in vertical migratory rhythms of benthopelagic shrimps Pasiphaea multidentata and P. sivado Jacopo Aguzzi*, Joan Baptista Company, Pere Abelló, José Antonio García Institut de Ciències del Mar (CSIC), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain *Email: jaguzzi@cmima.csic.es ABSTRACT: Vertical migratory rhythms of the western Mediterranean congeneric benthopelagic glass shrimps Pasiphaea sivado and P. multidentata were studied at depths of 400 to 430 m in relation to light intensity cycles (i.e. light regimes) in 2 different seasons: close to the autumn equinox (October) and to the summer solstice (June). Catches were considered a proxy of animal density close to the bottom and sampling was performed with consecutive epibenthic trawl hauls. These were continuously repeated over 4 d in order to determine the frequency and timing of species presence on the bottom. The density of animals present on the seabed at the time of the haul was estimated. In both P. sivado and P. multidentata marked diel differences in density were found which were correlated to variability in diel light intensity. While P. sivado was mostly captured at daytime in both seasons, regardless of size, P. multidentata only showed this pattern in the case of juveniles, i.e. individuals with carapace length <30 mm. Adult P. multidentata were mainly present on the bottom during the night, thus showing an apparent phase inversion in their movement patterns. This modification of diel behaviour can be interpreted as the result of differential habitat use with size/age. The comparison of present results with previous field studies illustrates that while P. sivado and juvenile P. multidentata perform actual vertical migrations, adults of the latter species undertake epibenthic movements along the bottom. KEY WORDS: Pasiphaea sivado · Pasiphaea multidentata · Ontogeny · Vertical migratory rhythms · Continental slope · Light intensity · Photoperiod length · Behavioural activity Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 335. Online publication date: April 16, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Decapod crustacean assemblages off the West coast of central Italy (western Mediterranean)

Community structure and faunal composition of decapod crustaceans off the west coast of central Italy (western Mediterranean) were investigated. Samples were collected during five trawl surveys carried out from June 1996 to June 2000 from 16 to 750 m depth. Multivariate analysis revealed the occurrence of five faunistic assemblages: 1) a strictly coastal community over sandy bottoms at depths Leptometra phalangium facies is found in many areas at depths between 120 and 180 m. The brachyuran crab Liocarcinus depurator dominates the shallow muddy-sandy bottoms of the shelf, while Parapenaeus longirostris is the most abundant species from the shelf to the upper slope assemblage. The dominant species on the middle slope are mainly nektobenthic ( Aristeus antennatus , Aristaeomorpha foliacea , Plesionika martia ), bentho-pelagic ( Pasiphaea sivado ) and benthic species ( Nephrops norvegicus ). The average diversity of the five assemblages defined increased with depth and the highest diversity values were found in the slope assemblages. Depth is the main factor influencing decapod assemblage composition, but sediment type and dissolved organic matter seem to be secondary structuring factors particularly in the shelf zone.

Feeding habits of the velvet belly lanternshark Etmopterus spinax (Chondrichthyes: Etmopteridae) off the Algarve, southern Portugal

Etmopterus spinax is one of the most abundant predators of the upper continental slope off the Algarve (southern Portugal), where it is captured in large quantities in deep-water fisheries. The feeding habits of E. spinax off the Algarve were investigated through the analysis of stomach contents of 376 individuals. Prey composition was described and maturity, sex and size related variations in the diet analysed. The overall diet of E. spinax suggested a fairly generalized benthopelagic foraging behaviour primarily tuned to pelagic macroplankton/microneckton, teleost fish and cephalopods. Sex and maturity related differences in the diet were not significant. Two main ontogenic diet shifts were observed at about 17 and 28 cm total length. Small and medium sized immature sharks had a diet dominated by eurybathic crustaceans, chiefly Meganyctiphanes norvegica and Pasiphaea sivado. Larger individuals consumed more teleosts and cephalopods, in part associated with scavenging as a new feeding strategy. With increasing shark size the diet diversified both in terms of resources exploited and prey size.

Trophodynamics of a deep-sea demersal fish assemblage from the bathyal eastern Ionian Sea (Mediterranean Sea)

Daily food consumption of the eight dominant demersal fish species of the bathyal eastern Ionian Sea were determined from field data on four seasonal cruises (April 1999, July August 1999, November 1999 and February 2000). Daily ration (DR) estimates ranged from 0.198 to 4.273% WW/WW. Overall, DR estimates were independent of the model used, and they were comparable to the daily consumption of other deep-sea fauna (e.g. fish and crustaceans). Both sharks studied ( Galeus melastomus and Etmopterus spinax) exhibited the highest values of DRs, together with the macrourid Coelorhynchus coelorhynchus in August. Among osteichthyes, DR estimates were related (in a multi-linear regression model) to the nature of their diet (i.e. their trophic level deduced from δ 15N isotopic composition, the mean number of prey and trophic diversity). Thus, species feeding at a lower trophic level, ingesting a large number of prey items and with a very diversified diet had higher DR than species from higher trophic level and feeding fewer prey items. By season, the DR of species feeding mainly on mesopelagic prey ( Hoplostethus mediterraneus and Helicolenus dactylopterus) were higher in summer, while DR for benthos/suprabenthos feeders (i.e. C. coelorhynchus and Nezumia sclerorhynchus) were higher in spring. Higher food consumption coincides with maximum food availability, both among mesopelagic feeders (higher availability of euphausiids, Pasiphaea sivado and Sergestes arcticus in summer) and among Macrouridae (higher suprabenthos densities in spring). In a tentative estimate the energy intake deduced from diet (i.e. mean energy value of food ingested) was constant in all seasons for each species studied. Results for the energy intake also indicate higher energy intake in the diet of mesopelagic feeders than in the diet of benthic feeders. Overall results are discussed in relation to the deep-sea ecosystem structure and functioning.

The diet of blue whiting, hake, horse mackerel and mackerel off Portugal

This paper deals with the diets of blue whiting Micromesistius poutassou (Risso 1810), hake Merluccius merluccius (L. 1758), horse mackerel Trachurus trachurus (L. 1758), and mackerel Scomber scombrus (L. 1758) off Portugal and explores variations in fish length, water depth, latitude and season. All four species feed on fish; however, hake and mackerel are the first and second most important predators, respectively, blue whiting being the most important fish prey for both species. The diets of blue whiting and horse mackerel are composed mainly of crustaceans. Diet variations according to predator fish size are more important than either latitude or depth. In the diets of blue whiting, hake and horse mackerel, prey importance increases with predator size. For blue whiting and horse mackerel, diet variations with fish length and water depth are correlated: small fish are closely associated with coastal areas where they feed on copepods and decapod larvae. Seasonality in the diet is apparent for blue whiting, hake and mackerel. For blue whiting, the decapod Pasiphaea sivado is the most important prey in summer and autumn, being replaced by the euphausid Meganyctiphanes norvegica in winter. In the diet of hake, seasonality was characterised by the major importance of Macroramphosus scolopax in autumn, whereas the diet of mackerel consisted of zooplankton in summer, fish and decapods in autumn and decapod larvae in winter. Seasonal changes in the diet of horse mackerel correspond to a higher diversity of prey in autumn compared to other seasons (although euphausids are the main prey in all seasons). Seasonality in feeding activity is not as marked for the other species as it is for horse mackerel; the percentage of empty stomachs of horse mackerel is greatest in winter, when spawning takes place at the Portuguese coast.

Biological patterns and near-bottom population characteristics of two pasiphaeid decapod crustacean species, Pasiphaea sivado and P. multidentata , in the north-western Mediterranean Sea

Biological aspects of the only two epi-/mesopelagic pasiphaeid species distributed along the continental marginof the north-western Mediterranean Sea were studied over the period 1991–1994. The annual reproductive cycle, reproductive output, sex and size distributions by depth (near-bottom distribution), and growth were analysed using 4156 specimens of Pasiphaeasivado (Risso, 1816) and 5491 specimens of P.multidentata Esmark, 1866. The reproductive cycle in the shallower-dwelling species, P.sivado, was nearly continuous, in contrast to the reproductive cycle in P.multidentata, which was markedly seasonal in nature. Both species exhibited similar size and population structure patterns with depth, with individual size increasing along the bottom depth gradient. The shallower-dwelling species had a significantly higher reproductive output level, in terms of the relative number of eggs, than the deeper-dwelling species. Biological trends for each of the species have been compared. The comparative results for these two congeneric species revealed that the biological parameters analysed were closely linked to their population structure. The slight differences in the depth range inhabited by each species have been considered the main environmental factor affecting the life histories of these two species. The data presented supported the hypothesis that depth exerted an important influence on the biological patterns of deep-water species, with the seasonality of reproductive processes increasing in deeper-dwelling species.

Megabenthic decapod crustacean assemblages on the Galician continental shelf and upper slope (north-west Spain)

The structure of megabenthic decapod crus- tacean assemblages on the Galician (north-west Spain) continental shelf (100 to 200 depth) and upper slope (200 to 500 m) was analyzed based on surveys carried out in autumn and spring, from 1980 to 1987. Forty species belonging to 19 families were caught. The portunid crab Polybius henslowii, a species with pelagic phases, was the most abundant species, but displayed strong spatial and temporal fluctuations. Other dominant species were the Norway lobster Nephrops norvegicus, the portunid Lio- carcinus depurator, the galatheids Munida intermedia and M. sarsi, and the shrimps Solenocera membranacea, Plesionika heterocarpus, Pasiphaea sivado and Dichelo- pandalus bonnieri. Total abundance and biomass (aver- age values excluding Polybius henslowii = 255 in- dividuals and 2.06 kg/30 min tow) and species richness and diversity, H' (6.85 species and H' = 1.45 per tow) displayed a significant positive correlation with depth, and strong interannual fluctuations. The factors de- termining community organization were depth and, to a lesser extent, spatial structure. There was clear evidence of bathymetric zonation, dierentiating between species characteristic of the slope (D. bonnieri and Pasiphaea sivado), shelf-slope edge (Macropipus tuberculatus, Pon- tophilus spinosus, Munida sarsi, S. membranacea, Pro- cessa spp.) and shelf (L. depurator, Macropodia tenuir- ostris, Paguridae and Chlorotocus crassicornis). The spatial zonation was related to changes in oceanography and sediment along the continental margin. Goneplax rhomboides, N. norvegicus, C. crassicornis and Alpheus glaber are benthic species which generally exhibit bur- rowing behaviour, and they were found mainly in the southern area where there are fine sediments due to the outwelling from the Rias Baixas. Dierent benthopelagic shrimps (Pontophilus spinosus, Plesionika heterocarpus, Processa spp. and Pasiphaea sivado) were typical of the zone just north of Fisterra, characterized by a con- vergence of water masses bringing about an increase in productivity due to upwelling. The benthic anomuran and brachyuran crabs Munida intermedia, M. sarsi, L. depurator and Macropipus tuberculatus were char- acteristic of the northwestern zone between Fisterra and Estaca, where the infauna reaches high biomass despite coarser sediments with a lower concentration of organic material than in the southern area. Lastly, both the Paguridae and Macropodia tenuirostris were species ty- pically found in the waters in the northern shelf. Based on interannual changes in assemblage structure, two periods could be distinguished: between 1980 and 1984, when Polybius henslowii, D. bonnieri and Pasiphaea si- vado had abundance peaks; and another period from 1985 to 1987 when L. depurator, Munida intermedia, M. sarsi and Macropipus tuberculatus increased in abundance.

Total and organic mercury concentrations in offshore crustaceans of the Ligurian Sea and their relations to the trophic levels

Total mercury and organic mercury were measured in five crustaceans representative of an offshore pelagic food web in the Gulf of Genoa, Italy: Meganycthiphanes norvegica, Gennadas elegans, Pasiphaea sivado, Pasiphaea multidentata and Aristeus antennatus. According to their predator-prey relationships, they represent three trophic levels in the Ligurian Sea. The concentrations of total and organic mercury increase with the trophic levels and with the weight of the specimens (except in G. elegans and in females of A. antennatus). However, at higher trophic levels the specimens are also larger. Only in P. sivado, do levels of inorganic mercury increase significantly (P = 0.001) with the size of the specimens. The ratio between organic mercury and total mercury did not increase with the trophic level.

Deep-water decapod crustacean communities in the Northwestern Mediterranean: influence of submarine canyons and season

The specific composition and abundance of bathyal decapods in the Catalan Sea were investigated. A total of 109 bottom trawls were effected at depths ranging from 141 to 730 m on the continental slope in the Catalan Sea (northwestern Mediterranean) during two sampling cruises in spring and autumn 1991. Multivariate analysis of the samples revealed four groups of the decapod crustacean communities: (1) A shelf-slope transition-zone group at depths between 146 and 296 m, primarily characterized by the presence of Plesionika heterocarpus; (2) an upper-slope community between 245 and 485 m, characterized by the presence of the mesopelagic species Pasiphaea sivado and Sergestes arcticus, with Processa nouveli, Solenocera membranacea and Nephrops norvegicus as secondary species; (3) a middle-slope community below 514 m, with Aristeus antennatus and Calocaris macandreae as the most abundant species; (4) a group at 430 to 515 m, comprising all samples collected exclusively within or in the vicinity of submarine canyons. Mesopelagic decapods were predominant on the slope, while benthopelagic fishes (Merluccius merluccius, Micromesistius poutassou, Gadiculus argenteus) replaced mesopelagic decapods on the shelf. There were seasonal variations, with higher densities of mesopelagic species in spring, which were probably related, among other factors, to variations in the photoperiod. Our surveys also revealed higher species richness in the canyons together with seasonal changes in the megafaunal biomass. Generally, the upper and middle-slope communities both displayed seasonal changes in the composition and abundance of megabenthos.

Spatial distribution of deep-sea decapods and euphausiids near the bottom in the northwestern Mediterranean

This study presents data on the occurrence and relative abundance of deep-sea decapod crustaceans and euphausiids, collected between 389 and 1859 m depth, in the water layer immediately adjacent to the bottom (10–140 cm above the bottom). Species were collected using an automatic opening and closing suprabenthic Macer-Giroq sledge in the Catalan Sea slope (western Mediterranean) during 1991 and 1992. The gear consisted of three rectangular mouths (40 × 80 cm) arranged in three tiers, one above the other, sampling simultaneously three separate levels (subsamples) between 10 and 50, 55 and 95, and 100 and 140 cm above the bottom. Results revealed how mesopelagic species [euphausiids, Sergestes arcticus Kroyer, Pasiphaea sivado (Risso), and Gennadas elegans (S.I. Smith)] and some nektobenthic species were concentrated in the uppermost levels, according to high values in indexes of swimming activity (K2, Kl). In contrast, endobenthic species (e.g. Calocaris macandreae Bell, Alpheus glaber (Olivi), and Crangonidae) were closely associated with the lowermost level. The partitioning of vertical space was analogous to that deduced from stomach contents analysis in deep-sea decapods in the same area. Almost all the specimens of Sergestes arcticus and Gennadas elegans captured were adults. The presence of large individuals of mesopelagic species near the sea floor is ascribed to ontogenetic migrations, which indicate differences between population structure of mesopelagic species near the bottom and in the midwater.

Seasonality of caridean decapod and mysid distribution and movements within the Severn Estuary and Bristol Channel

Mysids and caridean decapods are a significant proportion of the biomass within the Bristol Channel and Severn Estuary and key members of the marine food web in this estuarine system. Annual patterns of abundance at Hinkley Point Power Station of the mysids Praunus flexuosus, Schistomysis spiritus, Noemysis integer, Mesopodopsis slabberi and Gastrosaccus spinifer and of the carideans Pasiphaea sivado, Palaemon serratus, Pandalus montagui, Crangon crangon and C. allmani are examined. Using population age structures and sex ratios, the patterns of seasonal migration and recruitment are discussed.

Seasonality of caridean decapod and mysid distribution and movements within the Severn Estuary and Bristol Channel

Mysids and caridean decapods are a significant proportion of the biomass within the Bristol Channel and Severn Estuary and key members of the marine food web in this estuarine system. Annual patterns of abundance at Hinkley Point Power Station of the mysids Praunus flexuosus, Schistomysis spiritus, Noemysis integer, Mesopodopsis slabberi and Gastrosaccus spinifer and of the carideans Pasiphaea sivado, Palaemon serratus, Pandalus montagui, Crangon crangon and C. allmani are examined. Using population age structures and sex ratios, the patterns of seasonal migration and recruitment are discussed.

Day-night migrations by deep-sea decapod crustaceans in experimental samplings in the Western Mediterranean sea

Analysis of abundance and size frequency data on decapod crustacean species in two different habitats (inside and outside a submarine canyon) in the Western Mediterranean during two near-continuous 24-h sampling periods using commercial bottom trawls provided an indication of migratory ability and activity of the numerically dominant species. Certain nektobenthic species (e.g. Aristeus antennatus) carried out migrations up the slope at night. Mesopelagic species, represented mainly by Pasiphaea multidentata and Pasiphaea sivado, carried out vertical migrations, more clearly distinguishable in smaller individuals. Diel behaviour tended to differ inside and outside the canyon, and possible causes are mainly discussed in the light of the morphology and feeding ecology of the species considered.

Analysis of the structure of decapod crustacean assemblages off the Catalan coast (North-West Mediterranean)

We sampled the communities of decapod crustaceans inhabiting the depth zone between 3 and 871 m off the Catalan coast (North-West Mediterranean) from June 1981 to June 1983. The 185 samples comprised 90 species differing widely in their depth distributions. Multivariate analysis revealed four distinct faunistic assemblages, (1) littoral communities over sandy bottoms, (2) shelf communities over terrigenous muds, (3) upper-slope communitics, and (4) lower-slope or bathyal communities. The brachyuran crab Liocarcinus depurator is the most abundant species of the shelf assemblage, although L. vernalis dominates over the shallow sandy bottoms of the shelf. The dominant species of the upper-slope assemblage are nektobenthic species (Solenocera membranacea, Plesionika heterocarpus, Processa canaliculata), pelagic species (Pasiphaea sivado, Sergestes arcticus), and benthic species (Macropipus tuberculatus, Munida intermedia, Nephrops norvegicus). Aristeus antennatus comprise most of the biomass of the lower-slope community, which supports a greater diversity than the other assemblages. The main assemblages appear to be related to different hydrological characteristics, the extent of seasonal fluctuations, and to the changes in sediment structure associated with changes in the steepness of the bottom.