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1.
Ovarian tissue samples of Atlantic bluefin tuna (ABFT) spawners (n = 49) caught by purse seine in the Balearic Sea (western Mediterranean) were used to assess the stock reproductive characteristics. The frequency of spawning females estimated by the postovulatory follicle method was 84% and the spawning periodicity 1.2 days. Using an unbiased stereological method, the realized batch fecundity was estimated from counts of postovulatory follicles (POFs), whereas the batch fecundity of the subsequent spawn was estimated by quantification of the number of follicles containing oocytes at maturation stage (OMFs). The number of POFs was used as a reliable proxy of the realized batch fecundity, as it represents the actual number of eggs released in the last spawning event. The average relative realized batch fecundity was estimated to be approximately 48 eggs g− 1 of total body mass. While the absolute batch fecundity was isometrically related to the fork length, the relative batch fecundity was not dependent on fish size, which leads to the assumption that all length classes contribute proportionally to their size, towards the total number of eggs spawned by the broodstock. Size-related variations in the sex ratio were observed in the study area and in other Mediterranean locations; females were more abundant in mid-size classes while males predominated in large-size classes.  相似文献   

2.
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).  相似文献   

3.
《Journal of Sea Research》2011,65(4):494-504
Turbot (Psetta maxima Linnaeus) is a high value commercially exploited marine flatfish which occurs in European waters, from the Northeast Atlantic to the Arctic Circle, the Baltic and Mediterranean Sea. In Ireland, turbot are the most valuable commercial non-quota species. Very little is known about their population dynamics in the wild, in particular during the sandy beach nursery phase of the life history. In 2000, a survey was established to assess flatfish species on nursery grounds on the west coast of Ireland. Eleven sandy beaches were assessed for 0+ turbot by beach seining, over an eight year period (2000–2007) during the months of August and September. The objective of the study was to estimate juvenile turbot abundance and size structure to determine if any spatial and annual trends existed. Large scale variability in the recruitment of fish to nursery grounds may be indicative of fluctuations in the adult stock. Turbot were found to recruit to five beaches consistently over the eight year period. Temporal and spatial variability in the relative abundance and length of turbot was discerned, with no apparent overall trend. However, certain nursery grounds were shown in most of the years examined to support higher abundances of turbot in comparison to other areas over the eight year period. Turbot abundances on nursery grounds were significantly correlated with mean spring sea temperatures during the pelagic stage. The condition of turbot did not significantly differ on an annual or spatial scale. Mean densities of 0+ turbot along the Irish coast were found to be similar and at times higher than other areas in Europe, ranging from 0.1 (± 0.3) individuals 1000 m− 2 to 18.5 (± 6.9) individuals 1000 m− 2. Mean turbot total length on beaches ranged from 3.8 cm (± 0.6) to 6.6 cm (± 4.3). The observed spatial and temporal variability in abundance and length highlights the need for long-term studies when assessing juvenile flatfish populations. Results from the present study have provided much needed baseline data on wild juvenile turbot populations which is severely lacking for this species both on an Irish and on a European scale.  相似文献   

4.
Generally, estuarine intertidal mudflats constitute important nurseries for fish and foraging grounds for coastal birds by providing a plenitude of mollusks, worms, and crustaceans as prey, which in turn mostly feed on suspended and benthic microalgae, bacteria, and detritus. Despite the high productivity of such habitats, pronounced variability in both salinity and temperature results typically in low diversity. The only sea anemone reported from estuarine mud is the edwardsiid Nematostella vectensis Stephenson, 1935. It occurs widely in the northern hemisphere, and occasionally in extremely high density. Here we document another sea anemone from estuarine mud and muddy sand found in Southern Chile which has similar ecological attributes. Taxonomic confusion has impeded the reporting on this small but prominent member in a macrozoobenthic assemblage, the brooding Anthopleura hermaphroditica (Carlgren, 1899; Anthozoa: Actiniidae). It differs from N. vectensis by the presence of symbiotic algae. Average density under poly- to euhaline conditions in mud and muddy sand at around mid tide level was about 3 actinians per cm2. An average abundance of 11,000 m? 2, a biovolume of 487 cm3 m? 2, and a biomass of 35.5 g dry organic weight m? 2 were found in mud and muddy sand in two surveys 20 years apart. The mean fishing area of fully expanded individuals covers 42 ± 25 mm2, corresponding to a circular area with a diameter of 7.3 ± 5.7 mm. Preliminary experiments indicate that associated benthos may be relegated to life below surface by the net of tentacles above the sediment. As no predators on A. hermaphroditica could be found on the mudflat, the success of this mixotrophic sea anemone may entail a trophic dead end.  相似文献   

5.
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.  相似文献   

6.
Phosphine is a natural gaseous compound in the phosphorus biogeochemical cycle. This paper studies the spatial and temporal distributions of matrix-bound phosphine (MBP) and gaseous phosphine in the offshore area of the Southwest Yellow Sea, East Asia. The results show that MBP concentrations in marine surface sediments range from 0.69 ± 0.06 ng/kg (dry) to 179 ± 29 ng/kg (dry). Higher seasonal MBP concentrations in sediments are found in fall than in spring or winter in most sites. High MBP contents are observed in two fish-breeding areas. MBP concentrations decrease with distance to the coast, except in the southeast of the sampling area. MBP levels in marine sediments are found to be higher than those at several other places: freshwater sediments and soil, except eutrophic lakes. Gaseous phosphine contents in fall range from 0.14 ± 0.00 ng/m3 to 9.83 ± 0.97 ng/m3. No correlation is observed between MBP and gaseous phosphine.  相似文献   

7.
Reef researchers studying community shifts in the balance between corals and fleshy macroalgae have noted that algae are often covered with sediment. This study characterizes sediment trapping by macroalgae within a Hawaiian reef habitat and constrains the controls on this process. Sediment-laden macroalgae were sampled and macroalgal cover was assessed on a wide (∼1 km) reef flat off south-central Molokai. Macroalgae trapped a mean of 1.26 (±0.91 SD) grams of sediment per gram of dry weight biomass and that sediment was dominantly terrigenous mud (59% by weight). It was determined that biomass, as a proxy for algal size, and morphology were not strict controls on the sediment trapping process. Over 300 metric tons of sediment were estimated to be retained by macroalgae across 5.75 km2 of reef flat (54 g m−2), suggesting that this process is an important component of sediment budgets. In addition, understanding the character of sediment trapped by macroalgae may help constrain suspended sediment flux and has implications for nutrient dynamics in reef flat environments.  相似文献   

8.
To investigate the biological impact of polycyclic aromatic hydrocarbons (PAHs) on reproductive system, scallops Chlamys farreri were continuously exposed to benzo[a]pyrene (BaP) (0.5, 3, 10 μg L?1) during 15 days. DNA damage and histological alterations were examined in female gonad. DNA strand break levels significantly increased after 12 h exposure, and remained high and significantly different from control values until the end of the exposure. In the ovaries of the scallops exposed to 10 μg L?1 BaP for ten days, histological analysis showed that the cytoplasts of the oocytes in the outer layer of the ovaries became sparse, and the nuclear membranes were obscure. Damaging effects on ovaries and oocytes were more severe after 15 days exposure. Degenerating oocytes increased and the connective tissue of the ovary envelops became loose. Electron microscopic examination revealed ultrastructural aspects of degenerating oocyte and degenerated oocyte after 15 days exposure.  相似文献   

9.
Nutrient inputs associated with coastal population growth threaten the integrity of coastal ecosystems around the globe. In order to assess the threat posed by rapid growth in tourism, we analyzed the nutrient concentrations as well as the δ15N of NO3− and macrophytes to detect wastewater nitrogen (N) at 6 locations along a groundwater-dominated coastal seagrass bed on the Caribbean coast of Mexico. We predicted that locations with greater coastal development would have higher concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (P), as well as δ15N of NO3−, reflecting wastewater sources of N. However, concentrations of NO3− were not significantly different between developed (3.3 ± 5.3 μM NO3−) and undeveloped (1.1 ± 0.7 μM) marine embayments. The most important control on DIN concentration appeared to be mixing of fresh and salt water, with DIN concentrations negatively correlated with salinity. The δ15N of NO3− was elevated at an inland pond (7.0 ± 0.42‰) and a hydrologically-connected tide pool (7.6 ± 0.57‰) approximately 1 km downstream of the pond. The elevated δ15N of NO3− at the pond was paralleled by high δ15N values of Cladophora sp., a ubiquitous green alga (10 ± 1‰). We hypothesize that inputs of nitrogen rich (NO3− > 30 μM) groundwater, characterized by 15N enriched signatures, flow through localized submarine groundwater discharges (SGD) and contribute to the elevated δ15N signatures observed in many benthic macrophytes. However, changes in nitrogen concentrations and isotope values over the salinity gradient suggest that other processes (e.g. denitrification) could also be contributing to the 15N enrichments observed in primary producers. More measurements are needed to determine the relative importance of nitrogen transformation processes as a source of 15N to groundwaters; however, it is clear that continued inputs of anthropogenic N via SGD have the potential to severely impact ecologically and economically valuable seagrass meadows and coral reefs along the Caribbean coast of Mexico.  相似文献   

10.
The fate of terrigenous dissolved organic carbon (tDOC) delivered to the Arctic Ocean by rivers remains poorly constrained on both spatial and temporal scales. Early reports suggested Arctic tDOC was refractory to degradation, while recent studies have shown tDOC removal to be an active but slow process. Here we present observations of DOC, salinity, δ18O, and 228Ra/226Ra in the Polar Surface Layer (PSL) over the outer East Siberian/Chukchi shelf and the adjacent Makarov and Eurasian basins of the eastern Arctic Ocean. This off-shelf system receives meteoric water, introduced by rivers, after a few years residence on the shelf. Elevated concentrations of DOC (> 120 μM C) were observed in low salinity (~ 27) water over the Makarov Basin, suggesting inputs of tDOC-enriched river water to the source waters of the Transpolar Drift. The regression of DOC against salinity indicated an apparent tDOC concentration of 315 ± 7 μM C in the river water fraction, which is significantly lower than the estimated DOC concentration in the riverine sources to the region (724 ± 55 μM C). To obtain the timescale of removal, estimates of shelf residence were coupled with measurements of dissolved 228Ra/226Ra, an isotopic tracer of time since shelf residence. Shelf residence time coupled with DOC distributions indicates a first order tDOC removal rate constant, λ = 0.24 ± 0.07 yr-1, for the eastern Arctic, 2.5–4 times higher than rates previously observed in the western Arctic. The observed removal of tDOC in the eastern Arctic occurs over the expansive shelf area, highlighting the initial lability of tDOC upon delivery to the Arctic Ocean, and suggests that tDOC is composed of multiple compartments defined by reactivity. The relatively rapid remineralization of tDOC on the shelves may mitigate the strength of the Arctic Ocean atmospheric CO2 sink if a projected increase in labile tDOC flux occurs.  相似文献   

11.
《Journal of Sea Research》2007,57(2-3):162-170
Little attention has been paid to flatfish parasitism as a potential factor of variation in year-class strength. The aim of this study was to evaluate the relationship between parasitic infection and nutritional condition of young-of-year (YOY) common sole. Sole were collected monthly from May (early settlement) to November 2004 in a mussel pole culture area, using a push-net or a trawl, and dissected for parasite identification and counts. Total lipids were extracted from the whole body and lipid classes quantified. Triacylglycerols to sterols (free form) ratio (TAG/ST) was used as an index of nutritional status. Digenean metacercariae infection, characterized by two dominant genera, displayed clear seasonal dynamics and the highest records yet reported for sole. Prevalence (P%) and mean abundance (Ab ± SE) increased for Timoniella spp. (Acanthostomidae) from May (P% = 22%; Ab = 1.9 ± 1.1) to August (P% = 100%; Ab = 51.2 ± 10.4), and for Prosorhynchus spp. (Bucephalidae) from June (P% = 8%; Ab = 0.1 ± 0.0) to August (P% = 100%; Ab = 19.5 ± 1.7). Epidemiological values reached a plateau after August. In this shellfish-dominated nursery area, YOY sole accumulated metacercariae in the presence of the first intermediate hosts which live in the same habitat. Total lipids decreased significantly from May to June and then remained constant until autumn, indicating a change in the proximate composition of YOY during this high growth period. Mean (± SD) TAG/ST ratio increased from very low values in May–July (0.10 on average) to a peak in September (0.57 ± 0.31) and then fell back to values as low as before. YOY sole only stored energy as TAG prior to autumn. No relationship was found between YOY parasitic infection levels and lipid condition indices. However, the poor nutritional status and heavy infection level observed in November could dramatically lower over-winter survival of the YOY remaining in this shallow part of the nursery.  相似文献   

12.
An extended time series of particle fluxes at 3800 m was recorded using automated sediment traps moored at Ocean Station Papa (OSP, 50°N, 145°W) in the northeast Pacific Ocean for more than a decade (1982–1993). Time-series observations at 200 and 1000 m, and short-term measurements using surface-tethered free-drifting sediment traps also were made intermittently. We present data for fluxes of total mass (dry weight), particulate organic carbon (POC), particulate organic nitrogen (PON), biogenic Si (BSi), and particulate inorganic carbon (PIC) in calcium carbonate. Mean monthly fluxes at 3800 m showed distinct seasonality with an annual minimum during winter months (December–March), and maximum during summer and fall (April–November). Fluxes of total mass, POC, PIC and BSi showed 4-, 10-, 7- and 5-fold increases between extreme months, respectively. Mean monthly fluxes of PIC often showed two plateaus, one in May–August dominated by <63 μm particles and one in October–November, which was mainly >63 μm particles. Dominant components of the mass flux throughout the year were CaCO3 and opal in equal amounts. The mean annual fluxes at 3800 m were 32±9 g dry weight g m−2 yr−1, 1.1±0.5 g POC m−2 yr−1, 0.15±0.07 g PON m−2 yr−1, 5.9±2.0 g BSi m−2 yr−1 and 1.7±0.6 g PIC m−2 yr−1. These biogenic fluxes clearly decreased with depth, and increased during “warm” years (1983 and 1987) of the El Niño, Southern Oscillation cycle (ENSO). Enhancement of annual mass flux rates to 3800 m was 49% in 1983 and 36% in 1987 above the decadal average, and was especially rich in biogenic Si. Biological events allowed estimates of sinking rates of detritus that range from 175 to 300 m d−1, and demonstrate that, during periods of high productivity, particles sink quickly to deep ocean with less loss of organic components. Average POC flux into the deep ocean approximated the “canonical” 1% of the surface primary production.  相似文献   

13.
The reproductive biology of southern blue whiting (Micromesistius australis) inhabiting waters of the southwest Atlantic Ocean (52°‐53°S and 57°‐62°W) was studied through histological analysis of the ovaries. During 2003, the spawning peak occurred at the beginning of September south of the Malvinas Islands. Batch fecundity of this species ranged from 35 000 (41 cm total length, TL) to 245 000 (62 cm TL) oocytes and relative batch fecundity was 122 ± 43 (Mean ± SD, n = 24) oocytes per gram somatic weight. The average proportion of mature females with stage‐0 post‐ovulatory follicles was 0.25 for September 2003, which indicated a spawning frequency of 4 days during the peak of the season. Large females produced more egg batches than small spawners during the same period, but no significant relationship was found between oocyte dry weight and female size of southern blue whiting.  相似文献   

14.
Eighteen years of summertime hydrographic and chlorophyll-a (Chl-a) data (～2700 stations) from the South Shetland Islands (Antarctica) region show that a “bell-shaped” (unimodal) distribution of phytoplankton biomass results annually when plotted against the inshore to offshore gradient in surface salinity. The maximum for this unimodal Chl-a distribution corresponds with a shallow upper mixed layer (UML) in iron-rich waters that occurs at salinities ～34. Methods of gradient analysis are used to distinguish sources of variability for bloom development among years. The control of phytoplankton biomass is resolved across the salinity gradient that separates the co-limiting conditions of deep UML depths and low-iron concentrations as opposing end-members. Chlorophyll-fluorescence yield data (a proxy for Fe-stress) showed that at salinities ～34, phytoplankton biomass was unlikely to be limited by Fe. Instead, blooming at salinities ～34 (1.3±1 mg Chl-a m?3) co-varied with shallow UML depths (41±19 m) that occurred as a function of higher UML temperature (1.5±0.5 °C) among years, and is evidence that atmospheric climate variability impacts summertime phytoplankton biomass and production in this Southern Ocean seascape.  相似文献   

15.
《Marine and Petroleum Geology》2012,29(10):1838-1843
The hydrate-bearing sediments above the bottom simulating reflector (BSR) are associated with low attenuation or high quality factor (Q), whereas underlying gas-bearing sediments exhibit high attenuation. Hence, estimation of Q can be important for qualifying whether a BSR is related to gas hydrates and free-gas. This property is also useful for identifying gas hydrates where detection of BSR is dubious. Here, we calculate the interval Q for three submarine sedimentary layers bounded by seafloor, BSR, one reflector above and another reflector below the BSR at three locations with moderate, strong and no BSR along a seismic line in the Makran accretionary prism, Arabian Sea for studying attenuation (Q−1) characteristics of sediments. Interval Q for hydrate-bearing sediments (layer B) above the BSR are estimated as 191 ± 11, 223 ± 12, and 117 ± 5, whereas interval Q for the underlying gas-bearing sediments (layer C) are calculated as 112 ± 7, 107 ± 8 and 124 ± 11 at moderate, strong and no BSR locations, respectively. The large variation in Q is observed at strong BSR. Thus Q can be used for ascertaining whether the observed BSR is due to gas hydrates, and for identifying gas hydrates at places where detection of BSR is rather doubtful. Interval Q of 98 ± 4, 108 ± 5, and 102 ± 5, respectively, at moderate, strong and no BSR locations for the layer immediately beneath the seafloor (layer A) show almost uniform attenuation.  相似文献   

16.
Mass fluxes of diatom opal, planktonic foraminifera carbonate and coccolithophorid carbonate were measured with time-series sediment traps at six sites in the Arabian Sea, Bay of Bengal and Equatorial Indian Ocean (EIOT). The above fluxes were related to regional variations in salinity, temperature and nutrient distribution. Annual fluxes of diatom opal range between 3 and 28 g m−2 yr−1, while planktonic foraminifera carbonate fluxes range between 6 and 23 g m−2 yr−1 and coccolithophorid carbonate fluxes range between 4 and 24 g m−2 yr−1. Annual planktonic foraminifera carbonate to coccolithophorid carbonate ratios range between 0.8 and 2.2 and coccolithophorid carbonate to diatom opal ratios range between 0.5 and 3.3.In the western Arabian Sea, coccolithophorids are the major contributors to biogenic flux during periods of low nutrient concentrations. Coccolithophorid carbonate fluxes decrease and planktonic foraminiferal carbonate and diatom opal fluxes increase when nutrient-rich upwelled waters are advected over the trap site. In the oligotropic eastern Arabian Sea, coccolithophorid carbonate fluxes are high throughout the year. Planktonic foraminiferal carbonate fluxes are the major contributors to biogenic flux in the EIOT. In the northern and central Bay of Bengal, when surface salinity values drop sharply during the SW monsoon, there is a drastic reduction in planktonic foraminiferal carbonate fluxes, but coccolithophorid carbonate and diatom opal fluxes remain steady or continue to increase. Distinctly higher annual molar Sibio/Cinorg (>1) and Corg/Cinorg (>1.5) ratios are observed in the northern and central Bay of Bengal mainly due to lower foraminiferal carbonate production as a result of sharp salinity variations. We can thus infer that the enhanced freshwater supply from rivers should increase oceanic CO2 uptake. Its silicate supply favours the production of diatoms while the salinity drop produces conditions unfavourable for most planktonic foraminifera species.  相似文献   

17.
Atmospheric dry deposition of nitrogen (N) and dinitrogen (N2) fixation rates were assessed in 2004 at the time-series DYFAMED station (northwestern Mediterranean, 43°25′N, 7°52′E). The atmospheric input was monitored over the whole year. Dinitrogen fixation was measured during different seasonal trophic states (from mesotrophy to oligotrophy) sampled during nine cruises. The bioavailability of atmospherically deposited nutrients was estimated by apparent solubility after 96 h. The solubility of dry atmospheric N deposition was highly variable (from ∼18% to more than 96% of total N). New N supplied to surface waters by the dry atmospheric deposition was mainly nitrate (NO3−) (∼57% of total N, compared to ∼6% released as ammonium (NH4+)). The mean bioavailable dry flux of total N was estimated to be ∼112 μmol m−2 d−1 over the whole year. The NO3− contribution (70 μmol NO3− m−2 d−1) was much higher than the NH4+ contribution (1.2 μmol NH4+ m−2 d−1). The N:P ratios in the bioavailable fraction of atmospheric inputs (122.5–1340) were always much higher than the Redfield N:P ratio (16). Insoluble N in atmospheric dry deposition (referred to as “organic” and believed to be strongly related to anthropogenic emissions) was ∼40 μmol m−2 d−1. N2 fixation rates ranged from 2 to 7.5 nmol L−1 d−1. The highest values were found in August, during the oligotrophic period (7.5 nmol L−1 at 10 m depth), and in April, during the productive period (4 nmol L−1 d−1 at 10 m depth). Daily integrated values of N2 fixation ranged from 22 to 100 μmol N m−2 d−1, with a maximum of 245 μmol N m−2 d−1 in August. No relationship was found between the availability of phosphorus or iron and the observed temporal variability of N2 fixation rates. The atmospheric dry deposition and N2 fixation represented 0.5–6% and 1–20% of the total biological nitrogen demand, respectively. Their contribution to new production was more significant: 1–28% and 2–55% for atmospheric dry deposition and N2 fixation, respectively. The dry atmospheric input was particularly significant in conditions of water column stratification (16–28% of new production), while N2 fixation reached its highest values in June (46% of new production) and in August (55%).  相似文献   

18.
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.  相似文献   

19.
《Journal of Sea Research》2007,57(2-3):151-161
As part of the Danish restocking program, an experiment was carried out with four groups of turbot Psetta maxima released on two different occasions at the same location in Århus Bay, Denmark. One objective was to analyse the duration of post-release mortality and the magnitude of this mortality. In 2003 a group called Large turbot (17.1 cm total length (LT)) and a group called Intermediate (LT = 11.8 cm) were released, and in 2004 two similar-sized groups called Naive and Conditioned (LT = 9.8 cm) were released. The Conditioned differed from the Naive turbot by being transferred to enclosures at the release location six days prior to the actual release. This experiment was performed to investigate whether such a conditioning period had a positive effect on the survival and hence the success of the stocking. All the groups released were monitored daily until day 8, using a juvenile flatfish-trawl to recapture the fish. The catches were analyzed on the basis of a normal distribution approximation method, founded in diffusion theory, from which daily abundance of the released fish and hence post-release mortality could be estimated. The group of Large turbot suffered negligible post-release mortality, but for the Conditioned, Naive and Intermediate groups the loss varied between 34 and 66% d− 1. The mortality for the Conditioned group was found to be half that of the Naive turbot released simultaneously. The period of high post-release mortality was estimated to be restricted to three days after release. The only active predators observed in the area were birds. Besides estimating mortality the diffusion model provides an estimate on the catchability of the released turbot when fished with a juvenile flatfish-trawl. Catchabilities varied between 38 and 52% for all releases except for the 17 cm sized turbot released, where catchability was only 12%. The feeding performance of the released fish was also analysed and compared with that of wild fish caught at the same location. These results showed that the proportion of stomachs containing food increased not only with time after release, but also with the size of the turbot. However, whether or not fish was included in the diet was not related to size but to time after release and to whether they had been conditioned or not.  相似文献   

20.
Heat transports estimated CTD data collected during the World Ocean Circulation Experiment (WOCE) along the January 1993 30°S hydrographic transect (A10) and the output from a numerical model show a mean heat transport of 0.40 and 0.55±0.24 PW (standard deviation), respectively. The model shows a large annual cycle in heat transport (more than 30% of the variance) with a maximum (minimum) heat transport in July (February) of 0.68 (0.41) PW. Using these data, a method is proposed and evaluated to calculate the heat transport from temperature data obtained from a trans-basin section of expendable bathythermographs (XBTs) profiles. In this method, salinity is estimated from Argo profiles and CTD casts for each XBT temperature observation using statistical relationships between temperature, latitude, longitude and salinity computed along constant-depth surfaces. Full-depth temperature/salinity profiles are obtained by extending the profiles to the bottom of the ocean using deep climatological data. The meridional transport is then determined by using the standard geostrophic method, applying NCEP-derived Ekman transports, and requiring that the salt flux through the Bering Straits be conserved. The results indicate that the methods described here can provide heat transport estimates with a maximum uncertainty of ±0.18 PW (1 PW=1015 W). Most of this uncertainty is due to the climatology used to estimate the deep structure and issues related to not knowing the absolute velocity field and most especially characterizing barotropic motions. Nevertheless, when the methodology is applied to temperatures collected along 30°S (A10) and direct model integrations, the results are very promising. Results from the numerical model suggest that ageostrophic non-Ekman motions can contribute less than 0.05 PW to heat transport estimates in the South Atlantic.  相似文献   

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