Spatio-temporal variations in reproductive patterns and population structure of Pasiphaea multidentata (Decapoda: Caridea) in the Blanes canyon and adjacent margin, North-western Mediterranean Sea

Pasiphaea multidentata is a deep‐water caridean shrimp fished in the Mediterranean in association with the commercially exploited red‐shrimp Aristeus antennatus. A previous study describes seasonality in the reproductive pattern of P. multidentata using external morphological parametres. This study assesses the spatio‐temporal variations in the population structure, sex ratio, ovary cycle and gametogenesis of P. multidentata from three different fishing grounds in the Blanes canyon and adjacent margin (North‐western Mediterranean) over an annual cycle. The oogenetic pattern of this species is typical of a caridean shrimp. There is a pool of previtellogenic oocytes at all times that develop from the periphery of the gonad towards the centre during maturation. Previtellogenic oocytes grow to approximately 200 μm before undergoing vitellogenesis. The vitellogenic oocytes are surrounded by a monolayer of accessory cells. The maximum size observed for a mature oocyte was 1420 μm. The oocyte‐size distribution confirmed the seasonal reproductive pattern of this species; in winter, the ovaries contained mainly previtellogenic oocytes, some of which start maturing in spring, resulting in a slightly bimodal distribution. In summer, the vitellogenic oocytes reach approximately 1000 μm and in late autumn the ovaries are fully mature and ready to spawn. There were no significant differences in the reproductive and population structure patterns of P. multidentata among the three sites, suggesting that the population’s distribution is not affected by the geomorphology of the area, in particular the presence of the canyon. The populations are dominated by females at all sites and all seasons, with the arrival of juveniles in spring. The seasonal variations in the reproduction and recruitment of P. multidentata and the lack of spatial segregation within the population are discussed in terms of the species’ known biology, the effects of canyons in energy supply to the deep‐sea floor and the relationships of this species with the red‐shrimp A. antennatus.     

Nile damming as plausible cause of extinction and drop in abundance of deep-sea shrimp in the western Mediterranean over broad spatial scales

Greatly increased retention of flow in Nile River reservoirs was initiated in 1964, after completion of the Aswan High Dam, which induced important oceanographic changes in the Mediterranean Sea, including deep waters (below a depth of 150 m). Based on an analysis of data series starting in the 1940s/1950s, the giant red shrimp Aristaeomorpha foliacea has become locally extinct off of the Catalonian coasts (and elsewhere in the northwestern Mediterranean) at depths of 400–900 m, with a simultaneous and significant drop in the catches of red shrimp, Aristeus antennatus, in the second half of the 1960s. The extinction and sharp decline of deep-shrimp populations off Catalonian coast (at ca. 3200 km westwards from Nile Delta) followed the 1964 drop in Nile discharge with a delay of ca. 3–5 yrs (breakpoint analysis applied to data series). The breakpoints detected in the second half of 1960s both in Nile runoff and shrimps’ abundance were independent of climatic events in the study area (e.g. changes in NAO) and occurred before the increase in fishing effort off Catalonian coasts (breakpoint in 1973–1974). The Levantine Intermediate Water (LIW), inhabited by A. foliacea in the western Basin, had significant temperature (T) and salinity (S) increases in the 1950–1970 period, and Nile damming has contributed about 45% of the total S increase of Western Mediterranean deep-water masses from the 1960s to the late 1990s (Skliris and Lascaratos, 2004). This had to increase, for instance, LIW salinity at its formation site in the eastern Mediterranean. Nile damming was probably a triggering factor for the extinction/drop in abundance of deep-sea shrimp off Catalonian coasts.     

Dioxin compounds in the deep-sea rose shrimp Aristeus antennatus (Risso, 1816) throughout the Mediterranean Sea

Polychlorodibenzo-p-dioxins (PCDDs) and polychlorodibenzofurans (PCDFs) are among the more toxic anthropogenic contaminants. They are fat-soluble and accumulate in animal tissues. Exposure to PCDD/Fs can cause several endocrine, reproductive and developmental problems in animals, including human beings. Several studies have demonstrated that fish and invertebrates living in association with sediments are exposed to and accumulate contaminants, but to date there have been no studies of PCDD/Fs contamination in deep-sea regions. Specimens of Aristeus antennatus (Risso, 1816) were collected from depths of 600–2500 m at different points in the Mediterranean Sea, from the western basin off the coast of Barcelona to the central basin off the Peloponnesian Peninsula, with otter trawl gear. Amounts of PCDD/Fs were measured in different animal tissues by high resolution gas chromatography coupled to high resolution mass spectrometry (HRGC–HRMS). This is the first study to report the presence of PCDD/Fs in deep-sea organisms dwelling at depths below 600 m. A. antennatus presented levels of PCDD/Fs of the same order of magnitude, or slightly higher, as those found in shallow-water species (Melicertus kerathurus) with respect to land-generated contamination. This highlights the widespread distribution of these pollutants and the potential threat posed to the biodiversity of fragile and vulnerable ecosystems such as the deep-sea. PCDD/F levels detected in the edible parts (muscle) of the commercial shrimp A. antennatus were clearly below the toxic limit value established by European legislation. Levels followed the trend muscle<ovary<hepatopancreas, according to the lipid content of the organs in question. The specific profile of toxic PCDD/F congeners in the studied Penaeid shrimp specimens was characterized mainly by octachlorodibenzo-p-dioxin (OCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF) and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) congeners. Moreover, non 2,3,7,8-substituted congeners bioaccumulated in this species, as observed in shallow-water crustaceans. PCDD/Fs were found in the shrimp A. antennatus throughout the Mediterranean Sea. Total PCDD/Fs burdens were higher in shrimps caught in the western Mediterranean than in those caught at eastern Mediterranean sites. There was a tendency for higher levels of PCDD/F contamination in samples obtained from deeper (2500 m) than from shallower sites (600 m).     

Updating knowledge on growth,population dynamics,and ecology of the blue and red shrimp,Aristeus antennatus (Risso, 1816), on the basis of the study of its instars

Both national (GRUND) and international (MEDITS) trawl surveys carried out in the Italian seas since 1994 have produced consistent and rather homogeneous samples of red shrimps (per season, gear, and methods to ascertain abundance). Study and discussion of data regarding Aristeus antennatus (Risso, 1816) from Ligurian fishing grounds during the REDs project (FISH/2004/03‐32) made it possible to verify how key instars of the life of the female shrimp can be recognized from length frequency distributions derived from trawl surveys, allowing the age distributions to be split up. The segment of life that can be studied spans ages 1 and 10 and includes 20 instars, but larger sizes have been found which may extend the life span another 3 years. After age 5, only one growth instar per year occurs. Based on our study of the instars, we developed a size/age key for A. antennatus and used it to derive a von Bertalanffy growth function, total mortality rates and exploitation rates. Our results are related to basic biological and ecological characteristics of this species. Large individuals (females ≥50 mm CL at age 5 onward) present in a considerable percentage in the Ligurian Sea, are very important because (i) their fecundity is very high and therefore greatly influences the reproductive potential and (ii) they represent commercially the most valuable part of the catch. In addition, substantial relationships between the life history of A. antennatus and local oceanographic processes exist because the long life span of the species enlarges the area to which eggs and larvae are transported in surface currents, as well as the active return movements in deep waters where adult life mainly takes place. In the study area, the Northern Current provides the possibility of great horizontal displacement of A. antennatus eggs, larvae and early juveniles and, in general, attention to surface circulation may help to identify affinities in distant Mediterranean populations. This study presents A. antennatus in terms of a resource on the move at a Western Mediterranean scale.     

Transitory hydrographic structures and distribution of fish larvae and neustonic crustaceans in the north-western Mediterranean

A hydrographic and zooplankton survey (neuston and water column) was performed over the Blanes submarine canyon (western Mediterranean) in June 1993. Abundance of fish and crab larvae was very low when compared with previous studies conducted in the same area. The horizontal distribution of fish and crab larvae whose adults inhabit the continental shelf was restricted to the coast. The offshore occurrence of low-salinity waters of continental origin, together with the absence of a component perpendicular to the coast in the system of currents observed throughout the study area, support the observed pattern of distribution. The occurrence of mesopelagic fish larvae and of the oceanic neustonic isopod Idotea metallica in some coastal stations may be associated with episodic inshore-offshore exchanges of water masses identified by drifting buoy trajectories.     

Megabenthic diversity patterns and community structure of the Blanes submarine canyon and adjacent slope in the Northwestern Mediterranean: a human overprint?

The composition and structure of megabenthic communities in the Blanes canyon and adjacent open margin (Northwestern Mediterranean) were studied. The aim was to assess the effect of the canyon and commercial fishing intensity on the community composition and structure of benthic megafauna by (i) describing the megabenthic community composition, (ii) quantifying faunal abundance and biomass and (iii) describing community structure with MDS analyses and biodiversity indices. The results are compared between three sites (canyon head, canyon wall and open margin) located between 435 m and 700 m. Samples were collected using a commercial bottom trawl between April 2003 and March 2004. These sites are exploited by the local fishing fleet that targets the rose shrimp Aristeus antennatus . A total of 131 megabenthic species were identified from the three sites, with fishes and decapod crustaceans being the most speciose, most abundant and of higher biomass. The species richness, abundance and biomass of non-crustacean invertebrates were low. There were no significant differences in total abundance and biomass between the three sites. However, community structure analysis suggests that the open margin community is significantly different from the canyon head and canyon wall, with a lower species richness, lower diversity and lower evenness. The open margin community also reflects a higher degree of disturbance compared to the two canyon habitats. The results indicate that there is a canyon effect on the community structure of benthic megafauna, but this may be modulated by differing fishing pressure, which adds an additional factor to margin heterogeneity.     

New record of occurrence ofSergia lncens (Hansen) (crustacea,sergestidae) off Tung-kang,Taiwan, with special reference to phylogeny and distribution of the species

The commercially important sergestid shrimp,Sergia lucens (Hansen), has long been considered an endemic species of Japan because it had been found only in Suruga Bay and neighbouring waters. Recently, however, a considerable amount of a similar shrimp was caught by trawl nets off Tung-kang, southwestern Taiwan. This shrimp is distributed at depths of 100–300 m on the continental slope, around a deep submarine canyon adjacent to the mouth of the Kao-ping River. A morphological comparison with specimens from Suruga Bay reveals that the shrimp is identical toS. lucens. However, a slight difference in the patterns of water-soluble proteins was observed in a thin layer isoelectrophoretic examination. A difference was also observed in the spawning season of the two populations, indicating sexual and geographic isolation. Considering the distribution and phylogeny of the family Sergestidae, based on a possible evolutionary development from a benthic neritic organism to a pelagic oceanic one along the generaSicyonella-Sergestes-Sergia, it is assumed thatS. lucens entered a lower epipelagic habitat in the coastal waters from the warm oceanic mesopelagic habitat of the original stock. A hypothesis is proposed that speciation ofS. lucens from the original stock occurred when it was trapped in a semi-enclosed inlet (the paleo-East China Sea Gulf) that existed at the present Okinawa Trough during the late Pliocene to early Pleistocene. The inlet was deep, but had a neritic environment due to drainage from ancient large river systems, including the paleo-Yangtze River. The species expanded its distribution to the neighbouring waters during the warm interglacial period. However, a rapid rise in sea level after 14,000 years significantly changed the environmental conditions in the distributional area and the species could not expand into a neritic environment, which was too shallow for survival. Accordingly,S. lucens populations remained only in Suruga Bay and Tung-kang waters, where the environment has remained stable for the last 17,000 years or more. The two areas have the following common characteristics:

1. A large amount of fresh water is discharged into the deep submarine canyon adjacent to the river mouth.
2. The northeastern part is surrounded by land so that a direct inflow of boreal water into the environment is blocked.
3. Warm Kuroshio extension water intrudes and mixes with water from the rivers, and for Suruga Bay there is a current system that keeps distribution of the eggs and larvae restricted to the local habitats.

Taiwan annually exported some tens of metric tons of the driedS. lucens to Japan for the last few years, but the standing stock of Tung-kang waters is probably not as large as that in Suruga Bay.     

Anthropogenic CO2 fluxes in the Otranto Strait (E. Mediterranean) in February 1995

This study presents the distribution and fluxes of dissolved inorganic carbon (C_T), total alkalinity (A_T) and anthropogenic carbon (C_ant) along the Otranto strait, during February 1995. Based on a limited number of properties (temperature, dissolved oxygen, total alkalinity and dissolved inorganic carbon), the composite tracer TrOCA was used to estimate the concentration of anthropogenic CO₂ in the Otranto strait.Total alkalinity exhibits high values and weak variability throughout the water column of the strait, probably associated with the dense water formation processes in the Adriatic basin that induce a rapid transport of the coastal alkalinity to the deep waters. Elevated C_ant concentrations and high anthropogenic pH variations are observed in the bottom layer of the strait, associated with the presence of Adriatic Deep Water (ADW). The study shows that large amounts of C_ant have penetrated the highly alkaline Eastern Mediterranean waters, thereby causing a significant pH reduction since the pre-industrial era.Estimates of the transports of C_T and C_ant through the strait indicate that during February 1995, the Adriatic Sea imports through the Otranto strait natural and anthropogenic carbon and acts as a net sink of carbon for the Ionian Sea. The anthropogenic carbon that is imported to the Adriatic Sea represents less than 1% of the net C_T inflow. The Levantine Intermediate Water (LIW) contributes to about one-third of the total C_T and C_ant inflow. Although the amounts of C_ant annually transported by LIW and ADW are almost equal, the contribution of C_ant to the C_T transported by each water mass is slightly higher in ADW (3.1%) than in LIW (2.6%), as a result of its higher mean C_ant concentration. The ADW, despite its weak contribution to the total outflow of C_ant, has a vital role for the sequestration and storage of the anthropogenic carbon, as this water mass is the main component of the Eastern Mediterranean Deep Waters and, thus, the anthropogenic CO₂ is transferred in the deep horizons of the Eastern Mediterranean, where it remains isolated for many years.     

Particle fluxes dynamics in Blanes submarine canyon (Northwestern Mediterranean)

Within the framework of the multidisciplinary RECS project and with the aim of describing the particle flux transfer from the continental shelf to the deep basin, an array of five mooring lines equipped with a total of five pairs of PPS3/3 sequential-sampling sediment traps and RCM-7/8 current meters were deployed 30 m above the bottom from March 2003 to March 2004 inside and outside the Blanes Canyon. One mooring line was located in the upper canyon at 600 m depth, one in the canyon axis at 1700 m depth and other two close to the canyon walls at 900 m depth. A fifth mooring line was deployed in the continental open slope at 1500 m water depth.The highest near-bottom downward particle flux (14.50 g m⁻² d⁻¹) was recorded at the trap located in the upper canyon (M1), where continental inputs associated with the presence of the Tordera River are most relevant. On the other hand, the downward fluxes (4.35 g m⁻² d⁻¹) in the canyon axis (M2) were of the same order as those found in the western flank (M3) of the canyon. Both values were clearly higher than the value (1.95 g m⁻² d⁻¹) recorded at the eastern canyon wall (M4). The open slope (M5) mass flux (5.42 mg m⁻² d⁻¹) recorded by the sediment trap located outside the canyon system was three orders of magnitude lower than the other values registered by the inner canyon stations. The relevance of our data is that it explains how the transport pathway in the canyon occurs through its western flank, where a more active and persistent current toward the open ocean was recorded over the entire year of the experiment.Off-shelf sediment transport along the canyon axis showed clear differences during the period of the study, with some important events leading to strong intensifications of the current coupled with large transport of particle fluxes to the deepest parts of the canyon. Such events are primarily related to increases in river discharge and the occurrence of strong storms and cascading events during the winter.In summary, in this study it is shown that the dynamics of the water masses and the currents in the study area convert the sharp western flank of the Blanes Canyon in a more active region that favors erosion processes than the eastern flank, which has a smoother topography and where the absence of erosional conditions yields to steadier sedimentary processes.     

Nursery areas of red mullet (Mullus barbatus), hake (Merluccius merluccius) and deep-water rose shrimp (Parapenaeus longirostris) in the Eastern-Central Mediterranean Sea

The spatial pattern of the nursery areas of red mullet (Mullus barbatus), hake (Merluccius merluccius) (Linnaeus, 1758) and deep-water rose shrimp (Parapenaeus longirostris) (Lucas, 1846) was studied in the South Adriatic and North Ionian Seas (Eastern-Central Mediterranean) applying geostatistical techniques and data from time series trawl surveys conducted in the area. The analysed variables were: R (number of recruits/km²) and R/Tot (fraction of recruits on the total sampled population). The structural analysis showed a spatial pattern of both variables characterized by continuity on a small scale. Predictions of nursery area localization with probability of finding recruits at different threshold values were obtained through median indicator kriging. For the red mullet the nurseries were mainly identified in the South Adriatic Sea off the Gargano peninsula and between Molfetta and Monopoli within 50 m in depth. The main concentration of hake juveniles was found to be between 100 and 200 m in depth along the Gargano peninsula and between Otranto and Santa Maria di Leuca, where a nursery of deep-water rose shrimp was also detected. An overlapping depth, between 100 and 200 m, was identified for hake and deep-water rose shrimp nurseries. Protection of these areas through limitations of fishing pressure is discussed.     

Deep slope currents and suspended particle fluxes in and around the Foix submarine canyon (NW Mediterranean)

Deep slope currents and particulate matter concentrations were studied on the Barcelona continental margin in and around the Foix submarine canyon from May 1993 to April 1994. This year-long moored experiment revealed that near-bottom slope currents are strongly influenced by the bottom topography, being oriented along isobaths and along the canyon axis. The deep slope current fluctuations are controlled by the local inertial motion (18.3 h) and also by low-frequency oscillations at periods of 6–10 days, related to the passage of atmospheric pressure cells. Particulate matter concentrations recorded during the experiment do not show a clear seasonal variability, except outside the canyon, where significant peaks of particulate matter concentrations were recorded only during the winter-fall deployment. In addition, the temporal evolution of suspended particulate matter concentration is not linked to changes in the cross-slope or along-slope current components and did not show a clear relationship with river avenues or wave storm events. This suggests that suspended particulate matter exported from the shelf is dispersed on the slope by advective processes, which attenuate the signal of the shelf-slope sediment transfer. Mean particulate matter concentrations differed among sampling sites, but the magnitude of the mean horizontal suspended particle flux reflects a quite similar value in the whole study area, ranging from 2.53 to 4.05 mg m⁻² s⁻¹. These horizontal suspended particle fluxes are 27 (canyon head) to 360 (open slope) times higher than the settling particle fluxes measured at the same sampling sites, indicating that the suspended particulate transport on the Barcelona continental slope dominates over the settling particle fluxes, even inside the Foix submarine canyon.     

Contourite drift construction influenced by capture of Mediterranean Outflow Water deep-sea current by the Portimão submarine canyon (Gulf of Cadiz, South Portugal)

The margin of the Gulf of Cadiz is swept by the deep current formed by the Mediterranean Outflow Water (MOW) flowing from the Mediterranean to the Atlantic. On the northern margin of the Gulf (Algarve Margin, South Portugal), the MOW intensity is low and fine-grained contourite drifts are built up with an alongslope development. From new sedimentological data, this study emphasizes the presence of two types of contourite drifts separated only by a deep submarine canyon incising the slope with a north-south orientation (Portimão Canyon). High-resolution seismic and bathymetry interpretation shows that on the eastern side of the canyon, the MOW forms a thick and large detached drift (Albufeira Drift) prograding toward both north and west, as shown in seismic profiles, with a high sedimentation rate. On this side of the canyon, the MOW intensity is high enough to erode the slope forming a moat channel (Alvarez Cabral). On the western side of Portimão Canyon, the MOW energy is lower, preventing moat channel erosion. Only flat and thin drift develops (Portimão and Lagos Drifts) with slow aggradation and a low sedimentation rate. This difference in drift development is due to the presence of the canyon which generates an important change in hydrodynamic of the MOW, confirmed by temperature-density measurements showing that MOW flows down Portimão Canyon. The canyon is responsible for the deviation of the direction of the MOW as it partly catches the deep-sea current flowing westward (i.e. capture phenomenon). It creates, thus, a decrease of the flow energy, competency and capacity between the east and west sides of the canyon. Through this phenomenon of MOW deep-sea current capture, the canyon constitutes a morphologic feature generating an important change in the contourite deposition pattern.In addition to already known climatic and oceanographic influences, our results show the role of canyons on contourite drift building. This study provides new elements on autocyclic factors influencing the contourite sedimentation, which are important to consider in future sedimentary paleo-reconstruction interpretations.     

Genetic variability of the blue and red shrimp Aristeus antennatus in the Western Mediterranean Sea inferred by DNA microsatellite loci

Genetic variation at eight microsatellite loci was studied in nine populations of the blue and red shrimp Aristeus antennatus to investigate whether distinct stocks are present in the Western Mediterranean Sea. A high level of gene flow and no evidence of genetic partitioning were discovered. No significant variation was found (F_ST = 0.00673, P-value = 0.067) even when shrimps from exploited and those from deep-water unexploited grounds were compared. No evidence of reduction or expansion of population size in the recent past was found, as indicated by the bottleneck and interlocus g-tests. Our results are consistent with previous studies using mitochondrial gene methods and allozymes, indicating that, for this species, extensive pelagic larval dispersal and adult migration are probably responsible for the genetic homogeneity observed. In particular, due to a different bathymetric distribution of males and females, reported to be associated with different water masses and hence with possible differential dispersal capacity between sexes, the hypothesis of sex-biased dispersal was tested. Mean values of corrected assignment indices and mean relatedness values were higher for males, suggesting that females are the more widely dispersing sex. Molecular assessment of A. antennatus from the Western Mediterranean provides data of biological and evolutionary interest for the successful management of such a highly valuable fishery resource.     

High occurrence of the elasipodid holothurian Penilpidia ludwigi (von Marenzeller, 1893) in bathyal sediment traps moored in a western Mediterranean submarine canyon

One hundred and fifty specimens of the elasipod holothurian Penilpidia ludwigi (von Marenzeller, 1893) were collected in sediment traps moored near the seabed in the La Fonera Canyon (Catalan Sea, north-western Mediterranean) and on the adjacent continental slope. These provide the third record of this apparently endemic Mediterranean species and the first record from the western Mediterranean. This was the only holothurian species trapped and the most abundant macroscopic organism found in the traps between 1200 and 1700 m depth over the whole sampling period (March–November 2001). It was particularly abundant in spring during the main flux of organic particles in the canyon. This coupling suggests that Penilpidia may aggregate at the seafloor during these events, making food availability a plausible explanation of the seasonal occurrence. Lateral transport of material re-suspended locally or up-canyon by near bottom currents appear to be the mechanism behind this uncommon occurrence, although in situ observations have recently been made on the swimming capability of this holothurian. The occurrence of benthic organisms in sediment traps set close to the seabed can provide information on bathyal benthic and benthopelagic populations.     

Isolation By Distance (IBD) signals in the deep-water rose shrimp Parapenaeus longirostris (Lucas, 1846) (Decapoda,Panaeidae) in the Mediterranean Sea

The identification of boundaries of genetic demes is one of the major goals for fishery management, and few Mediterranean commercial species have not been studied from a genetic point of view yet. The deep-water rose shrimp Parapenaeus longirostris (Lucas, 1846) is one of the most important components of commercial landings in Mediterranean, its fishery aspects have received much attention, regrettably without any concern for the genetic architecture of its populations. The population structure in the central and eastern Mediterranean Sea (captures from six Italian and two Greek landings) has been analysed on the basis of surveys carried out with mitochondrial and AFLP markers. Data revealed the presence of a gradual discrepancy along a west–east axis. This species, occurring mainly at a depth of between 100 and 400 m, is not strongly confined in isolated demes, but it demonstrates an ‘Isolation By Distance’ model, within the Mediterranean Sea, which includes geographical areas with a some degree of isolation. The role of hydrodynamic forces, such as currents, water fronts, is discussed; and a further evidence of the ‘Levantine isolation’ within Mediterranean basin is shown.     

Additional evidence of LIW entrainment across the Algerian subbasin by mesoscale eddies and not by a permanent westward flow

The circulation of the Levantine Intermediate Water (LIW) in the Algerian subbasin (western basin of the Mediterranean sea) has been much debated for more than fifteen years now. Together with the old circulation diagrams, several numerical models claim that a branch of LIW is permanently flowing westwards across the Algerian subbasin, i.e. directly from the Channel of Sardinia towards the Strait of Gibraltar. Only a few models support the fact that the unique continuous flow of LIW is structured as an alongslope counterclockwise vein, which is thus directed northwards off Sardinia in the Algerian subbasin, and hence support the diagram published by Millot in 1987 [Millot, C. (1987a) Circulation in the Western Mediterranean. Oceanologica Acta 10(2), 143–149]. According to this diagram, any little mixed LIW found in the central subbasin corresponds to fragments which have been pulled away from the vein and entrained there by mesoscale eddies originated from the Algerian Current. The ELISA experiment (1997–1998), as a follow-up of other ones conducted since about 15 years, was designed partly to validate the diagram. In addition to about 40 current meters set in place for one year, four main campaigns were conducted with a sampling strategy guided in real time by infrared satellite information. The data set we present clearly provides additional evidence that the little mixed LIW found in the central Algerian subbasin has been entrained there by the mesoscale eddies and not by a permanent westward flow.     

The feeding and diet of the deep-sea shrimp Aristeus antennatus off the Balearic Islands (Western Mediterranean): Influence of environmental factors and relationship with the biological cycle

Spatio-temporal variation of feeding intensity and diet in the red shrimp Aristeus antennatus was studied at two locations around the island of Mallorca (Balearic Islands, Western Mediterraean) in August, September, and November 2003, and in February, April and June 2004 at depths between 550 and 750 m. The two areas, with different oceanographic conditions, were respectively located in the northwest (Sóller) and the south (Cabrera) of Mallorca. Off Sóller, feeding intensity of A. antennatus showed a significant increase from February to April and June 2004 in all the three size-classes studied (small shrimps: CL < 30 mm; medium: CL between 30 and 40 mm; large: CL ? 40 mm). Off Cabrera, the highest fullness was recorded in November 2003 among small and medium shrimp, while only large specimens showed patterns similar to that found off Sóller. Off Sóller, the diet of both small (CL < 34 mm) and large (CL ? 34 mm) A. antennatus was mainly influenced by season, with three dietary groups corresponding to August-September 2003, to November 2003/February 2004, and to hauls from April to June 2004. Off Cabrera, hauls (representing diets) were grouped by depth, never by season. The most remarkable seasonal shift in the diet of A. antennatus off Sóller was the increase of mesopelagic prey in April-June relative to other months. In all size categories there was an increase off Sóller in the energy intake of prey ingested from February to June 2004, an increase not found off Cabrera. Degree of digestion of mesopelagic prey indicated nocturnal feeding on mesopelagic fauna. These prey probably have a shallower depth distribution at night than found in our daylight sampling, and possible migratory movements among prey and A. antennatus at night would explain the lack of correlation between prey abundance in guts and in the environment found during daylight periods for most micronekton mesopelagic prey (euphausiids, myctophids and sergestids). Off Sóller, fullness and diet were significantly linked to temporal changes in water column productivity (e.g., Chl a readings, fluorescence) and to changes in the shrimp biology (lipid content of hepatopancreas, Gonado-somatic Index, GSI). Off Cabrera, we found a higher dependence of fullness and diet with T and S, both variables in turn related to depth. The increase of stomach fullness and dietary energy intake in pre-reproductive females from February to April-June 2004 found off Sóller, coupled with the consumption of mesopelagic prey, was parallel to a significant increase of the gonad weight (GSI, fecundity) in June. Most individuals attain gonad development in the period May-June, after two months of the peak of primary production at the surface. The strong link found between pelagic resources and reproductive processes in a deep-sea species such as the shrimp Aristeus antennatus, situated near the top of the trophic web, suggests a rapid energy flow via mesopelagic fauna between surface primary production and bathyal megabenthic communities at oligotrophic insular areas. In contrast to mainland areas off the Catalan coasts submitted to the influence of submarine canyons, around the island of Mallorca the empoverishment of benthos biomass may enhance consumption of micronektonic prey and a possible accumulation of pre-reproductive females of A. antennatus in areas (e.g., steep slopes and persistent frontal systems found off Sóller) with high zooplankton aggregations.     

XBT monitoring of a meridian section across the western Mediterranean Sea

During the Thetis-2/MAST-2 tomography experiment, T7-XBT calibrated (accuracy ∼0.05°C) probes were launched ∼28 km apart between France and Algeria, twice a month from Feb. to Sep. 1994. Combined with infrared images, altimetric data and ship drifts, they provide definite information on the structure, drift and role of the eddy-like mesoscale phenomena generated by the Algerian Current instability. When embedded in this alongslope current, these phenomena generally propagate downstream at a few km/day and are markedly asymmetrical. Because of the topography in the eastern part of the Algerian Basin, they separate from the current, become more symmetrical and follow an anticlockwise circuit in the open basin. These phenomena are deeper than ∼750 m and entrain seaward pieces of the Levantine Intermediate Water (LIW) vein flowing along the Sardinian slope, thus being responsible of the large spatial and temporal variability of the LIW distribution in the open basin. The non-existence of a LIW vein flowing westward across the Algerian Basin is definitely demonstrated. In the Gulf of Lions, new insights are provided into the formation and spreading of the Winter Intermediate Water (WIW), which is the Western Mediterranean counterpart of LIW. Considering the large amount of WIW formed during this mild winter, it is clear that this water has not received enough attention yet, and is certainly a major component of the Mediterranean outflow at Gibraltar. Finally, the XBT data account for the eastward flow of the Western Mediterranean Deep Water (WMDW) off Algeria.     

闽东近海游泳动物群落组成、资源量与生物多样性的时空格局研究

采用底拖网方法调查研究了闽东近海春季(5月)和秋季(10月)游泳动物群落组成、生物多样性、资源密度及时空分布格局等问题。调查中出现游泳动物70种(鱼类47种,甲壳类18种,头足类5种),隶属于15目40科64属,以鲈形目种类最多(25种)。鱼类是主要游泳动物群落,春季鱼类个体数和重量分别占总渔获的66.4%和72.3%,甲壳类分别占比33.4%和26.9%,头足类分别占比0.2%和0.8%;秋季,上述三个类群在总渔获中的占比分别为56.6%和60.4%、42.0%和37.8%以及1.4%和1.8%。春季优势种包括红狼牙虎鱼(Odontamblyopus rubicundus)、三疣梭子蟹(Portunus trituberculatus)、孔虎鱼(Trypauchen vagina)等10种,秋季优势种为龙头鱼(Harpadon nehereus)、三疣梭子蟹、六指马鲅(Polynemus sextarius)等7种;两个季节共有优势种包括三疣梭子蟹、日本 (Charybdis japonica)、龙头鱼、棘头梅童鱼(Collichthys lucidus)和六丝钝尾虎鱼(Amblychaeturichthys hexanema)5种。秋季的生物多样性指数和均匀度指数高于春季。春季平均资源密度为1013.7kg/km~2和10.2×10~4ind/km~2,高于秋季的平均值(899.0kg/km~2和6.6×10~4ind/km~2)。总体而言,鱼类是闽东近海主要的游泳动物类群,其资源密度从近岸向外海呈降低趋势,春季的资源密度高值出现在闽东外海中部水域,秋季高值则出现在南部的闽江口等水域;其春季的优势种种类多于秋季,存在一定程度季节性更替现象。     

Zooplankton communities and oceanographic structures in a high-resolution grid in the south-eastern corner of the Bay of Biscay

A one year long monthly sampling series at a fixed station was combined with a high-spatial resolution survey (May 2003) to investigate factors controlling zooplankton distribution in the south-eastern corner of the Bay of Biscay. Species abundance and gonad maturity for Calanoides carinatus and Calanus helgolandicus were estimated to clarify whether the observed spatial patterns were attributable to increased population growth or to mechanical accumulation. The two studies included distinct oceanographic regimes. The eastern corner of the grid was characterized by Adour river plume waters and the Cap Breton canyon, and the rest of the area by an alternating pattern of physical convergences and divergences. In the river plume, the zooplankton community diversity and abundances were highest in response to the nutrient enriched river plume waters and the submarine canyon. In the rest of the area, distribution and abundance patterns were the result of a combination of behaviour and physical transport.