Reproductive pattern and egg development of the deep-sea crab Paromola cuvieri (Brachyura,Homolidae) around the Canary Islands (NE Atlantic)

This work investigated the biology of Paromola cuvieri in the Atlantic Ocean, including reproductive patterns, sex structure, depth distribution and egg development. Females were more abundant than males, mainly at depths greater than 600 m. Males were dominant in size classes larger than 110 mm carapace width (CW), especially over 120 mm, for which only males were observed. The mean length of both sexes decreased with depth. P. cuvieri appears to have continuous reproduction throughout the year. Large females tend to spawn mainly between summer and winter, but smaller females spawn during the summer. Four maturity categories were identified based on the ovary colour, and these categories were histologically validated. Three categories of testes were identified according to their colour and morphology. Sexual maturity was estimated at sizes between 71.6 and 74.0 mm CW for females and at 91.0 mm CW for males. The relative growth showed changes along the ontogeny, at 73.6 mm CW (females) and 91.3–92.2 mm CW (males). Egg development appears to not be completely synchronous, and two colour patterns can be observed simultaneously. Four stages of egg development were found: eggs undivided and fully filled with yolk in orange egg masses; eggs with a free region of yolk visible in orange or red egg masses; embryos with slightly pigmented, crescent-shaped eyes in brown egg masses; and embryos with visible pigmented structures, enlarged eyes, segmented appendages and abdomen in brown egg masses. The mean number of external eggs carried by females in stage I was estimated to be 315,753±19,267. Three species of barnacle were observed on the exoskeleton: Poecilasma aurantia, Poecilasma crassa and Heteralepas microstoma (Cirripedia, Thoracica).     

The dynamics of postovulatory follicle degeneration and oocyte growth in Baltic sprat

Ovaries of Baltic sprat (Sprattus sprattus balticus S.) were analysed histologically to identify stages of postovulatory follicles (POF) and to assess the oocyte development pattern. Samples were taken every 3 h during a 24 h trawl survey conducted in the Bornholm Basin in April 2007. Gonad histology revealed spawning of sprat throughout the day which hampered the exact ageing of POFs by the postovulatory follicle method and therefore did not allow direct estimation of spawning frequency. However, it was possible to define four stages of POFs, according to their histological features. The occurrence of these POF stages (I to IV) corresponded clearly to the development of the leading oocyte cohort. Further, the oocyte recruitment pattern revealed that the spawning batch can be identified prior to hydration. The POF stages I and II were present almost exclusively in vitellogenic ovaries, POF III were found in ovaries in the germinal vesicle stage, and the most deteriorated POF stage IV was found in actively spawning fish with hydrated oocytes. Since POF were absent only in very few ovaries (5%), and in each ovary in general only one POF stage was present, the duration of POF degeneration approximately equals the average batch interval, i.e. the time lag between subsequent spawning events. The results of the present study will serve as basis for future studies on Baltic sprat oocyte recruitment and daily spawning fraction.     

Identifying spawning events in the Japanese flounder Paralichthys olivaceus from depth time-series data

Vertical swimming events (VSEs) of the Japanese flounder, Paralichthys olivaceus, recorded by high-frequency depth data loggers, were analysed to identify spawning events. In total 25,907 VSEs from 10 adult fish were classified into 4 clusters using a k-means method. VSEs in a specific cluster (cluster-S) characterised by accelerated vertical swimming were identified as possible spawning events. Both the descent (0.43 ± 0.22 body length s^− 1) and ascent rates (0.43 ± 0.24 body length s^− 1) of VSEs in cluster-S were more than 4 times faster than in any other VSE. Our analyses indicated that 4 individuals exhibited the spawning events during the recording periods. The estimated spawning frequency ranged from 0.74 to 0.90 events day^− 1. These values were comparable to those obtained in other field and laboratory studies. The spawning condition of fish at the time of recapture was confirmed by separate histological and anatomical observations, which supported the cluster analysis results. These results suggest that a clustering technique can be successfully applied to identify spawning behaviour from time-depth data of free-swimming flatfishes that exhibit vertical swimming movements.     

Population structure and life history of Hemimysis lamornae mediterranea (Malacostraca: Mysida) in the Ebro Delta (NW Mediterranean)

Hemimysis lamornae mediterranea Bacescu, 1936 has been recently reported in the Ebro Delta (Spain, NW Mediterranean). Little is known about the biology and ecology of this mysid and we provide the first information about its population biology. H. l. mediterranea were collected from Sant Carles de la Ràpita harbor from June 2010 to March 2012 at night. The H. l. mediterranea population was composed of two main individual size categories: larger-sized winter/spring individuals and smaller-sized spring/summer individuals. The overall sex ratio is highly skewed; mature females are 2.5 times more abundant than mature males. Reproductive activity was higher during late winter and spring but was almost continuous throughout the year. The intra-marsupial development and growth of juveniles has been studied in the laboratory. The mean duration of incubation period (intra-marsupial stages) in laboratory conditions was 11 days (20 °C) and the age at first maturity ranged from14 to 20 days. The growth rate was faster in early juveniles and declined with age, showing a maximum of 0.152 mm d^− 1. The laboratory results and demographic data suggest that H. l. mediterranea will produce several generations per year in the Ebro Delta. H. l. mediterranea was characterized by a combination of early maturation of individuals (short juvenile period), rapid growth, small adult size, a continuous reproduction all year round, iteroparous females, a relatively high fecundity and a high number of generations per year.     

Life history of the deep-sea cephalopod family Histioteuthidae in the western Mediterranean

The life cycle of the two species of the deep-sea family Histioteuthidae inhabiting the Mediterranean Sea (Histioteuthis reversa and Histioteuthis bonnellii) was studied from monthly samples taken throughout the year during daytime hours by bottom trawl gears. A small sample of individuals found floating dead on the sea surface was also analyzed. Both species were caught exclusively on the upper slope at depths greater than 300 m. Their frequency of occurrence increased with depth and showed two different peaks, at 500–600 m and 600–700 m depth in H. bonnellii and H. reversa, respectively, which might indicate spatial segregation. Maturity stages were assigned using macroscopic determination and confirmed with histological analyses. Although mature males were caught all year round, no mature females were found, which suggests that their sexual maturation in the western Mediterranean takes place deeper than the maximum depth sampled (800 m). In fact, the increase in mean squid size with increasing depth in H. reversa indicates an ontogenetic migration to deeper waters. The individuals of both species found floating dead on the sea surface were spent females which had a relatively large cluster of small atresic eggs and a small number of remaining mature eggs scattered in the ovary and mantle cavity. The sizes of these females were clearly larger than the largest individuals caught with bottom trawls. A total of 12 and 7 different types of prey, belonging to three major taxonomic groups (crustaceans, osteichthyes and cephalopods), were identified in the stomach contents of H. reversa and H. bonnellii, respectively. In both species fishes were by far the main prey followed by crustaceans, whereas cephalopods were found only occasionally. The preys identified, mainly myctophids and natantian crustaceans, indicate that both histioteuthids base their diet on pelagic nictemeral migrators.     

Egg production of turbot,Scophthalmus maximus,in the Baltic Sea

In the brackish water Baltic Sea turbot spawn at ~ 6–9 psu along the coast and on offshore banks in ICES SD 24–29, with salinity influencing the reproductive success. The potential fecundity (the stock of vitellogenic oocytes in the pre-spawning ovary), egg size (diameter and dry weight of artificially fertilized 1-day-old eggs) and gonad dry weight were assessed for fish sampled in SD 25 and SD 28. Multiple regression analysis identified somatic weight, or total length in combination with Fulton's condition factor, as main predictors of fecundity and gonad dry weight with stage of maturity (oocyte packing density or leading cohort) as an additional predictor. For egg size, somatic weight was identified as main predictor while otolith weight (proxy for age) was an additional predictor. Univariate analysis using GLM revealed significantly higher fecundity and gonad dry weight for turbot from SD 28 (3378–3474 oocytes/g somatic weight) compared to those from SD 25 (2343 oocytes/g somatic weight), with no difference in egg size (1.05 ± 0.03 mm diameter and 46.8 ± 6.5 μg dry weight; mean ± sd). The difference in egg production matched egg survival probabilities in relation to salinity conditions suggesting selection for higher fecundity as a consequence of poorer reproductive success at lower salinities. This supports the hypothesis of higher size-specific fecundity towards the limit of the distribution of a species as an adaptation to harsher environmental conditions and lower offspring survival probabilities. Within SD 28 comparisons were made between two major fishing areas targeting spawning aggregations and a marine protected area without fishing. The outcome was inconclusive and is discussed with respect to potential fishery induced effects, effects of the salinity gradient, effects of specific year-classes, and effects of maturation status of sampled fish.     

Reproductive patterns of the abyssal asteroid Styracaster elongatus from the N.E. Atlantic Ocean

We analysed the reproductive biology of the asteroid species Styracaster elongatus based on time-series samples from a 5000-m-deep site on the Porcupine Abyssal Plain (N.E. Atlantic). The ratio of males to females, the gonadosomatic index (GI), and pyloric caecum index (PCI) were determined and the results were corroborated by histological examination of the gonads. Fecundity and oocyte-size distribution were determined by histological and image analyses. Styracaster elongatus is a gonochoric asteroid and the ratio of males to females was not significantly different throughout the year. Oogenesis was asynchronous. The previtellogenic oocytes grew to a size of ～230 μm before undergoing vitellogenesis. Maximum oocyte size was ～620 μm. The ovary volume was mainly occupied by small previtellogenic oocytes (100–150 μm) at any one time. Mean GI was 6.38±3.30 for females and 9.04±4.1 for males. Mean PCI was 7.44±1.66 for females and 7.66±1.46 for males. Mean fecundity was 16,373±5988 oocites per female. There were no seasonal variations in GI and fecundity. There was evidence of a pyiloric caecum seasonal development for females and males. For S. elongatus there is no direct relationship among seasonal primary production at the surface and production of vitellogenic oocytes. Nevertheless, this species takes advantage of the pulse of phytodetritus to the seabed by increasing the storage of nutrients in the pyloric caecum in order to maintain a constant production of eggs and sperm.     

Reproductive biology of Ilisha elongata (Teleostei: Pristigasteridae) in Ariake Sound,Japan: Implications for estuarine fish conservation in Asia

Elongate ilisha (Ilisha enlongata) is a commercially important species that contributes to clupeoid fisheries in Asian countries. In the present study, the reproductive biology of I. elongata in Ariake Sound, Japan is determined for the first time. Six maturity stages were described using ovarian and testicular histology throughout the annual cycle. The spawning season in Ariake Sound lasts from May to July, with peak spawning activity in May and June. Age at first maturity was estimated to be 2 years, with a few exceptions of 1 year in well-developed males. Ovaries that contained both tertiary yolk oocytes and postovulatory follicles occurred from late May to late July, indicating that I. elongata is a multiple spawner. The size–frequency distribution of oocytes provided evidence for its multiple spawning and accuracy of the fecundity estimates. The batch fecundity of this species was estimated at between 22,200 and 270,900 eggs per individual, increasing with age between two and six years. The present findings on the reproductive strategy of I. elongata in Ariake Sound are generally consistent with those in temperate or subtropical populations, but quite different from those of tropical population where first maturation occurs around 200 days and life spans are shorter, with a maximum age less than 3 years. The conservation implications of this reproductive strategy in a harsh, variable environment in Asian countries are also discussed.     

Potential transport of plaice eggs and larvae between two apparently self-contained populations in the Irish Sea

A coupled physics particle-tracking model, driven by realistic meteorological forcing was used to examine the dispersal and transport of plaice eggs and larvae in the year 2000 from two spawning grounds in the Irish Sea. The model included passive transport of eggs and early stage larvae, diel vertical movements for larvae between 7 and 10.5 mm in body-length and tidally synchronised, vertical movements for larger larvae (>9 mm body-length). The year 2000 was chosen because of the availability of ichthyoplankton data with which to initialise the model. The majority of larvae originating from spawning in the eastern Irish Sea settled into nursery grounds along the Scottish, English and Welsh coasts, in agreement with previous findings. In contrast, a significant portion of larvae originating from spawning in the western Irish Sea was transported eastwards to these same nursery grounds. Transport across the Irish Sea resulted from the onset of tidally synchronised vertical behaviour encoded in the model for older larvae. Settlement of larvae into local nursery grounds along the Irish coast was limited. Because of the prevailing winds and currents in the region, plaice eggs and larvae are unlikely to be transported from east to west; in most years spawning in the western Irish Sea probably acts as an additional source of juveniles for nursery grounds along the Scottish, English and Welsh coasts.     

Atmospheric input of dissolved inorganic phosphorus and silicon to the coastal northwestern Mediterranean Sea: Fluxes,variability and possible impact on phytoplankton dynamics

One hundred twelve rainwater samples collected from 1986 to 2003 at the signal station of Cap Ferrat (France, NW Mediterranean coast) were analysed for phosphate and silicate contents. This sampling site is affected by a European urban-dominated background material, with episodic Saharan dust inputs. The input of dissolved inorganic phosphorus (DIP) and dissolved inorganic silicon (DISi) was calculated. The most significant loadings of DIP and DISi were selected in order to assess their potential impact on phytoplankton dynamics, particularly in oligotrophic conditions, when surface waters are nutrient-depleted. The theoretical new production triggered by DIP and DISi inputs (NP_atmo) was estimated through Redfield calculations. The maximum theoretical DIP-triggered NP_atmo was up to 670 mg C m⁻² in October, at the end of the oligotrophic period (135 mg C m⁻³ in the 5 m-thick surface layer). During the same period, the daily integrated primary production measured at the DYFAMED site (NW Mediterranean Sea) was on average 219 mg C m⁻² d⁻¹ within the 0–100 m depth water column, while the mean daily primary production in the 5 m-thick surface layer was 1.6 mg C m⁻³ d⁻¹. However, high NP_atmo due to high DIP inputs might be episodically limited by lower DISi inputs, which may consequently lead to episodic preferential growth of non-siliceous phytoplanktonic species.     

Microbial respiration in the Levantine Sea: evolution of the oxidative processes in relation to the main Mediterranean water masses

First data on microbial respiration in the Levantine Sea are reported with the aim of assessing the distribution of oxidative processes in association with the main Mediterranean water masses and the changing physical structure determined by the Eastern Mediterranean Transient. Respiratory rates, in terms of metabolic carbon dioxide production, were estimated from measured electron transport system activities in the polygonal area of the Levantine Sea (32.5–36.5 N Latitude, 26.0–30.25 E Longitude) and at Station Geo’95, in the Ionian Sea (35°34.88 N; 17°14.99 E). At the Levantine Sea, the mean carbon dioxide production rate decreased from the upper to the deeper layers and varied from 22.0±12.4 μg C h⁻¹ m⁻³ in the euphotic layer to 1.30±0.5 μg C h⁻¹ m⁻³ in the depth range between 1600 and 3000 m. Significant differences were found among upper, intermediate and bottom layers. The euphotic zone supported a daily carbon dioxide production of 96.6 mg C d⁻¹ m⁻² while the aphotic zone (between 200 and 3000 m) sustained a 177.1 mg C d⁻¹ m⁻² carbon dioxide production. In Station Geo’95, the carbon dioxide production rates amounted to 170.4 and 102.2 mg C d⁻¹ m⁻² in the euphotic and aphotic zones, respectively. The rates determined in the identified water masses showed a tight coupling of respiratory processes and Mediterranean circulation patterns. The increasing respiratory rates in the deep layers of the Levantine Sea are explained by the introduction of younger waters recently formed in the Aegean Sea.     

DOC dynamics in the meso and bathypelagic layers of the Mediterranean Sea

Seven years (2001–2008) of dissolved organic carbon (DOC) vertical profiles were examined in order to assess the main processes determining DOC concentration and distribution in the meso- and bathypelagic layers of the Mediterranean Sea. As expected, DOC showed high and highly variable concentrations in the surface layer of 57–68 μM (average values between 0 and 100 m), with a decrease to 44–53 μM between 200 and 500 m. Deep DOC distribution was strongly affected by deep-water formation, with a significant increase to values of 76 μM in recently ventilated deep waters, and low concentrations, comparable to those observed in the open oceanic waters (34–45 μM), where the oldest, deep waters occurred. In winter 2004/2005 a deep-water formation event was observed and the consequent DOC export at depth was estimated to range between 0.76–3.02 Tg C month^–1. In the intermediate layer, the main path of the Levantine Intermediate Water (LIW) was followed in order to estimate the DOC consumption rate in its core. Multiple regression between DOC, apparent oxygen utilization (AOU), and salinity indicated that 38% of the oxygen consumption was related to DOC mineralization when the effect of mixing was removed. In deep waters of the southern Adriatic Sea a DOC decrease of 6 μM, together with an AOU increase of 9 μM, was observed between the end of January 2008 and the end of June 2008 (5 months). These data indicate a rate of microbial utilization of DOC of about 1.2 μM C month⁻¹, with 92% of the oxygen consumption due to DOC mineralization. These values are surprisingly high for the deep sea and represent a peculiarity of the Mediterranean Sea.     

Dissolved and particulate organic carbon and nitrogen in the Northwestern Mediterranean

The distribution of dissolved organic carbon (DOC) and nitrogen (DON) and particulate organic carbon (POC) and nitrogen (PON) was studied on a transect perpendicular to the Catalan coast in the NW Mediterranean in June 1995. The transect covered a hydrographically diverse zone, including coastal waters and two frontal structures (the Catalan and the Balear fronts). The cruise was conducted during the stratified period, characterized by inorganic nutrient depletion in the photic zone and a well established deep chlorophyll a maximum. DOC concentrations were measured using a high-temperature catalytic oxidation method, and DON was determined directly, with an update of the Kjeldahl method, after removal of inorganic nitrogen.The ranges of DOC and DON concentrations were 44–95 μM-C and 2.8–6.2 μM-N. The particulate organic matter ranged between 0.9 and 14.9 μM-C and from 0.1 to 1.7 μM-N. The DOC : DON molar ratio averaged 15.5±0.4, and the mean POC : PON ratio was 8.6±0.6. The distribution of dissolved organic matter (DOM) was inverse to that of the salinity. The highest concentrations of DOM were found in coastal waters and in the stations affected by the Catalan front, located at the continental shelf break.It was estimated that recalcitrant DOM constituted 67% of the DOM pool in the upper 50 m. The data suggest that accumulation of DOC due to the decoupling of production and consumption may occur in the NW Mediterranean during stratification and that the organic matter exported from the photic layer is dominated by C-rich material.     

Total organic and inorganic carbon exchange through the Strait of Gibraltar in September 1997

The total organic carbon (TOC) and total inorganic carbon (C_T) exchange between the Atlantic Ocean and the Mediterranean Sea was studied in the Strait of Gibraltar in September 1997. Samples were taken at eight stations from western and eastern entrances of the Strait and at the middle of the Strait (Tarifa Narrows). TOC was analyzed by a high-temperature catalytic oxidation method, and C_T was calculated from alkalinity–pH_T pairs and appropriate thermodynamic relationships. The results are used in a two-layer model of water mass exchange through the Strait, which includes the Atlantic inflow, the Mediterranean outflow and the interface layer in between. Our observations show a decrease of TOC and an increase of C_T concentrations from the surface to the bottom: 71–132 μM C and 2068–2150 μmol kg⁻¹ in the Surface Atlantic Water, 74–95 μM C and 2119–2148 μmol kg⁻¹ in the North Atlantic Central Water, 63–116 μM C and 2123–2312 μmol kg⁻¹ in the interface layer, and 61–78 μM C and 2307–2325 μmol kg⁻¹ in the Mediterranean waters. However, within the Mediterranean outflow, we found that the concentrations of carbon were higher at the western side of the Strait (75–78 μM C, 2068–2318 μmol kg⁻¹) than at the eastern side (61–69 μM C, 2082–2324 μmol kg⁻¹). This difference is due to the mixing between the Atlantic inflow and the Mediterranean outflow on the west of the Strait, which results in a flux of organic carbon from the inflow to the outflow and an opposite flux of inorganic carbon. We estimate that the TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varies from (0.97±0.8)10⁴ to (1.81±0.90)10⁴ mol C s⁻¹ (0.3×10¹² to 0.56×10¹² mol C yr⁻¹), while outflow of inorganic carbon ranges from (12.5±0.4)10⁴ to (15.6±0.4)10⁴ mol C s⁻¹ (3.99–4.90×10¹² mol C yr⁻¹). The high variability of carbon exchange within the Strait is due to the variability of vertical mixing between inflow and outflow along the Strait. The prevalence of organic carbon inflow and inorganic carbon outflow shows the Mediterranean Sea to be a basin of active remineralization of organic material.     

Diel variation in the vertical distribution of particulate matter (>0.15 mm) in the NW Mediterranean Sea investigated with the Underwater Video Profiler

Day/night variations in the size distribution of the particulate matter >0.15 mm (PM) were studied in May 1995 during the DYNAPROC time-series cruise in the northwestern Mediterranean Sea. Data on vertical distributions of PM (>0.15 mm) and zooplankton were collected with the Underwater Video Profiler (UVP). The comparisons of the UVP data with plankton net data and POC data from water bottles indicated that more than 97% of the particles detected by the UVP were non-living particles (0.15 mm) and that the PM contributed 4–34% of the total dry weight measured on GF/F filters. Comparison of seven pairs of day and night vertical profiles performed during the cruise showed that in the upper 800 m, the mean size and the volume of particles was higher at night than during the day. During the night, the integrated volume of the PM increased on average by 32±20%. This increase corresponded to a shift of smaller size classes (<0.5 mm) towards the larger ones (>0.5 mm). During the day, the pattern was reversed, and the quantity of PM >0.5 mm decreased. During the study period, the standing stock of PM (60–800 m) decreased from 7.5 to less than 2 g m⁻² but the diel variations persisted, except for two short periods in the superficial layer following a wind event. The cyclic feeding activity induced by the diel vertical migration of zooplankton could be the best candidate to explain the observed diel fluctuations in the size classes of PM in the water column. However, our results also suggest that in the upper layer additional driving forces such as the increase of the level of turbulence after a wind event or the modification of the zoo- and phytoplankton community can influence the PM temporal evolution.     

New and regenerated production in the Almeria-Oran front area,eastern Alboran Sea

Uptake and regeneration of nitrogen in the Almeria-Oran frontal zone (SW Mediterranean) and adjacent (Atlantic and Mediterranean) systems were studied during the Almofront I cruise (JGOFS-France). The frontal zone was characterized by an upsloping of nitracline from about 50 m in the adjacent systems to 25–30 m within. Along with nitrate, ammonium, chlorophyll a and particulate organic nitrogen also were at higher concentrations in the frontal zone than in the adjacent waters.The nitrate uptake rates were significantly higher in the frontal zone (up to 6.4 nmol l⁻¹ h⁻¹) than in the Atlantic and Mediterranean waters (generally <1 nmol l⁻¹ h⁻¹) indicating a significant increase of new production at the front. This increase was related to the upsloping of the nitracline as shown by the significant correlation (p<0.05) between new production and depth of the nitracline. The new production in the Almeria-Oran was much lower than those recorded in other oceanic and coastal fronts. This could be related to the fact that the nitracline did not rise up to the surface and the high concentrations of nitrate were confined to deeper layers where the ambient light intensity was less. Nitrate uptake in the frontal zone was significantly higher, by 1.7–5.8 times (average 4.2), than the calculated diffusive flux of nitrate, suggesting that vertical advection may be an important source of nitrate. New production rates at the front were also significantly higher (3–9 times, average 5.8) than the PON flux to 100 m depth estimated by sediments traps (Journal of Marine Systems 5, 377–389), suggesting a strong decoupling between surface production and downward flux of POM in the frontal zone.The north–south gradient observed with different parameters indicates the presence of a transfrontal secondary circulation. This distribution also suggests that the primary production in the front is initially nitrate-based, with a diatom-herbivore food chain, whereas regenerated production, associated with an intense recycling of organic matter, later becomes progressively important in time and space.     

Life history of the bathyal octopus Pteroctopus tetracirrhus (Mollusca,Cephalopoda) in the Mediterranean Sea

The life cycle of the deep-sea octopus Pteroctopus tetracirrhus was studied from monthly samples obtained throughout the year in different areas of the western Mediterranean (mainly around the Balearic Islands and along the coast of the Iberian Peninsula). A total of 373 individuals (205 females, 168 males) were analyzed; females ranged from 4.5 to 14.0 cm mantle length (ML) and males from 4.5 to 11.5 cm ML. There were few small-sized octopuses (<7 cm ML) in the samples, which might indicate that these individuals inhabit rocky grounds that are not accessible to trawlers or waters deeper than the maximum depth sampled (800 m). The species occurred more frequently around the Balearic Islands than along the Iberian Peninsula as they appeared in 20% and 7%, respectively, of the hauls in these areas. The octopus inhabits the lower continental shelf and upper slope in both areas, primarily between 200 and 500 m depth. Modal lengths were followed from autumn, when recruits were caught by trawlers, to summer, when reproduction took place. Females grew from 8 to 10 cm ML from winter to spring, but this modal size did not increase further in summer; males grew from 7 to 9 cm ML from winter to spring. The total disappearance of large individuals after summer suggests a life cycle lasting a single year. The evolution of the monthly mean sizes showed that the growth was best described by log-linear functions in both sexes. The length at first maturity was clearly higher in females (12 cm ML) than in males (8 cm ML). A total of 30 different prey items, belonging to four major taxonomic groups (crustaceans, osteichthyes, cephalopods and gastropods), were identified in the stomach contents. The diet of the octopus was based on crustaceans and teleosts, which accounted for 75% and 23% of the prey items, respectively. Cephalopods and gastropods were accessory prey as they only represented 1.6% and 0.7%, respectively, of the total. The octopus showed a marked preference for the benthic fish Symphurus nigrescens and the endobenthic crustacean Alpheus glaber. The bathymetric distribution of P. tetracirrhus coincides with those of these two main prey, which suggests that the distribution of the octopus might be strongly linked to its trophic resources.     

Vertical distribution of zooplankton in Canary Island waters: implications for export flux

Zooplankton biomass, gut fluorescence and electron transfer system (ETS) activity were measured in vertical profiles (0–900 m) in two different size classes (<1 and >1 mm) in Canary Island waters. Both size fractions displayed a typical pattern of distribution with higher biomass, gut fluorescence and ETS in the shallower layers at night. By day, however, the vertical distribution varied between the size fractions, with higher biomass of the small fraction in the 0–200 m and a layer of large organisms at depth (∼500 m). For both size fractions, average ETS activity was higher by day than at night at depths between 200 and 600 m. Similarly, gut fluorescence was slightly higher by day below 200 m. The downward export of respiratory carbon was 1.92 and 4.29 mg C m⁻² d⁻¹ for samples obtained southwest of Gran Canaria Island and west of Tenerife Island respectively, being 2.68 mg C m⁻² d⁻¹ for the whole area. These values represented 16–45% (22–28% for the area) of the calculated passive particulate export production resulting from primary production. The estimated “gut flux” accounted for 0.35 (western zone) and 2.37 mg C m⁻² d⁻¹ (southwest of Gran Canaria), being 1.28 mg C m⁻² d⁻¹ for the whole area and represented between 3 and 25% (11–14% for the whole area) of the estimated passive particle export flux. These results agree with previous estimates and suggest that diel-migrant zooplankton can play an important role in the downward flux of carbon.     

Acoustic discrimination of two zooplankton species (mysid) at 38 and 120 kHz

Using bifrequency sonar (38 kHz, 120 kHz) directed towards the open sea from the inside of a submarine cave, two species of Mysidacea (Crustacea), similar in shape but not in size, and with different patterns of behaviour, were observed simultaneously and discriminated, and their biomass was estimated during their migration. The first species, Hemimysis speluncola (<1 cm length), lives in the submarine cave, forming a distinct community that migrates horizontally. The second species, Siriella jaltensis (>1 cm length), lives in the open sea and migrates vertically. These species are both detected clearly at 120 kHz, but only the larger one, Siriella jaltensis, is detected at 38 kHz. This distinction allows one to determine the size limits of planktonic objects detected at these frequencies, i.e. 3 mm at 120 kHz and 10 mm at 38 kHz, corresponding to one quarter of the wavelength. The target strength (TS) of each species was calculated from the field data and compared to results calculated from three models. As the volume of the cave occupied by the Hemimysis population is about 300 m³, and the density of the swarm is 36,000 individuals/m³, the number of individuals in the cave is estimated to be around 10 million (or 24 kg). The density of the open-water population of Siriella is estimated to be 13 individuals/m³.     

Reproductive traits of tropical deep-water pandalid shrimps (Heterocarpus ensifer) from the SW Gulf of Mexico

Heterocarpus ensifer is a tropical deep-water pandalid shrimp whose reproductive features are poorly known. We examined reproductive traits of a population of H. ensifer inhabiting the continental slope (311–715 m in depth) off the Yucatan Peninsula, Mexico (SW Gulf of Mexico). Size range of the total sample (n=816) was 10.4–38.9 mm carapace length. Females grow larger than males, but both sexes mature at 57% of their maximum theoretical size and at ～30% of their total lifespan. Among adult females, the proportion of ovigerous females was high in all seasons, indicating year-round reproduction. Most females carrying embryos in advanced stages of development had ovaries in advanced stages of maturation, indicating production of successive spawns. In the autumn, however, the proportion of ovigerous females and the condition index of these females were lower compared to other seasons. This pattern potentially reflects a reduction in food resources following the summer minimum in particulate organic carbon flux to the deep benthos, as reported in previous studies. Spawns consisting of large numbers (16024±5644, mean±SD) of small eggs (0.045±0.009 mm³) are consistent with extended planktotrophic larval development, an uncommon feature in deep-water carideans. Egg number increased as a power function of female size but with substantial variability, and egg size varied widely within and between females. There was no apparent trade-off between egg number and egg size and neither of these two variables was influenced by female condition. These results indicate iteroparity and a high and variable reproductive effort, reflecting a reproductive strategy developed to compensate for high larval mortality. The present study provides a baseline to compare reproductive traits between Atlantic populations of this tropical deep-water pandalid.