Dynamics of growth and maturation in the cephalopod Illex argentinus de Castellanos, 1960 (Teuthoidea: Ommastrephidae)

first_imgPost-recruit Illex argentinus were collected from the fishery on the Patagonian Shelf between 1986 and 1988. Age was determined by analysis of daily growth increments in ground sections of the statolith, female fecundity was determined, specimens were dissected, weighed and assigned a maturity stage. The relation between mantle length and age is best approximated by a linear model. Both sexes live approximately one year. Females grow faster and attain a larger size than males, but males mature younger. Hatching occurs during the austral winter, peaking in June-July. There is a consistent trend of increasing growth rate with later date of hatching. Statolith growth is negatively allometric with body growth and there is greater divergence between statolith and body growth in females. In post-recruit Illex growth in mass of somatic tissues, apart from the digestive gland, approximates isometry with growth of the whole body. Growth of the digestive gland and the reproductive organs is positively allometric with growth in whole body mass. There is poor correlation between the mass of female reproductive organs and whole body mass, which is due to differences in size at maturity. Mating rarely occurs on the feeding grounds. Fecundity of fully mature females in the sample falls in the range 113835-246098 eggs per individual. This possibly underestimates average fecundity because mature squid on the feeding grounds may be precocious and smaller than average at full maturity. A model combining absolute and relative growth, predicts average male and female growth and growth of the major somatic and reproductive organs. This poorly predicts average female maturity indices with age because of variability in mass of the female reproductive organs. A model that treats maturity stages separately gives close agreement with measured mass of the reproductive organs and maturity indices of a mature female at age one year. Females invest approximately 20% of total body mass in gonad and accessory reproductive organs at full maturity.last_img read more

Mechanism for the behavior of hydroactive materials used in humidity sensors

first_imgThe theory of operation of humidity sensors has not been widely discussed in the literature. In particular, no convincing explanation has been given as to why they respond to relative humidity (RH) rather than to an absolute measure of humidity, such as vapor pressure or mixing ratio, over a wide temperature range. A simple mechanism based on the adhesion of surface water to polarized solids is presented that explains many of the properties of these sensors.last_img

The occurrence of monounsaturated n-C21 and polyunsaturated C25 sedimentary hydrocarbons in the lipids of Antarctic marine organisms

first_imgAntarctic zooplankton have been found to be a potential source of sedimentary hydrocarbons. Monounsaturated C21 n-alkenes and highly branched polyunsaturated C25 n-alkenes were analysed in the aliphatic fraction of the lipids of Antarctic pelagic and inshore marine organisms. Cluster analysis of the species-based data set produced four main groups: phytoplankton, epipelagic herbivores, epipelagic carnivores and mesopelagic omnivores. The detailed pattern of alkenes exhibited differences within the groups and also with tissue type (krill, Euphausia superba). The origin of alkenes in Antarctic biota appeared to be either synthesis de novo or due to the condensation of smaller molecules. Formation of alkenes by the decarboxylation of fatty acids was not consistent with the hydrocarbon and fatty acid composition of Antarctic zooplankton. There was no evidence for direct assimilation of C21 and C25 alkenes by zooplankton or higher predators from their diet. Zooplankton C25 alkenes are probably transported unaltered directly to the sediment as detritus or via predators in faecal material. Sedimentary C25 alkenes are proposed as biomarkers of recent zooplankton activity in the water column.last_img read more

Interannual variability in the early growth rate and size of the Antarctic fish Gobionotothen gibberifrons (Lönnberg)

first_imgGobionotothen gibberifrons <1 year old, of the 1977, 1980, 1981, 1985, 1986, 1990 and 1995 cohorts, were sampled using nets, in various periods during summer (December to February) at South Georgia. Growth in standard length (Ls) was estimated using the exponential model. Among the seven cohorts, average growth rate varied between 0.33–2.1% Lsd−1, and predicted Ls for mid-January varied between 21.6–29.1 mm. Average growth rate was inversely related to mean date of sampling but was not significantly related to mean Ls. Mean sea surface temperatures were available for the 1981–95 cohorts. Average growth rate and predicted Ls for mid-January were both negatively conelated with mean December–January sea temperature, but were not significantly related to mean weekly sea surface temperature during the sampling periods. Greater average growth rate and greater Ls in cooler summers may be partly due to a large-scale pattern of environmental variability, indicated by sea temperature, that governs the timing and magnitude of the production cycle and food availability.last_img read more

factors affecting primary molt in the gray-headed albatross

first_imgThe mean number of primaries molted by Gray-headed Albatrosses (Diomedea chrysostoma) varied with year and previous breeding experience independently, but was not related to individual reproductive success over a longer period. Within each category of breeding experience, birds renewed fewer primaries during the “poor” year of 1994, when subsequent reproductive success was only 27%, than in 1993 when subsequent reproductive success was 57%. Inspection of individual feathers indicated that the outer primaries were least likely to be renewed during the period of stress. Within each year, birds that failed in their breeding attempt during the previous year renewed fewer feathers than those which reared a chick two years previously, a difference which was probably partly related to the time available for molting. In 1994 only, the date of failure in the previous year was inversely related to the number of primaries molted by males. The arrival mass of males was positively correlated with the number of primaries molted in two out of four seasons. Males and females molted similar numbers of primaries.last_img read more

The Trans-Mars Expedition – a long-distance, long-duration, scientific EVA

first_imgOf Martian expeditionary accomplishments, the Trans-Mars Expedition is the most audacious in terms of the logistical challenges imposed upon it and diversity of scientific foci it could encompass. The similar to21,000 km expedition requires two transpolar assaults on the Martian north and south geographical poles, a traverse across the summit of Mount Olympus and traverses across the interconnecting desert regions of Mars. Taking lessons suggested for Martian desert, polar and mountain expeditions, I describe this expedition using a 120degreesW, 300degreesW longitudinal route. I quantify the in-situ resource utilization (ISRU) requirements for oxygen, water and fuel. Calculations suggest that ISRU of the martian atmosphere can be used to supply vehicle fuel and to replenish oxygen and water throughout the expedition duration at mean rates of progress and with certain assumptions on oxygen and water usage. Equipment requirements are reviewed with a special focus on equipment that can be modified for use in all of the environments encountered. As its scientific objective, the expedition would undertake a study of volcanism, desert and polar processes over a planetary transect contributing significantly to the inventory of samples gathered across the Martian surface. The planning of such an expedition provides a reference expedition for considering ISRU and scientific requirements for any long-duration, long-distance scientific expeditionary EVA on Mars.last_img read more

Results from the implementation of the Elastic Viscous Plastic sea ice rheology in HadCM3

first_imgWe present results of an implementation of the Elastic Viscous Plastic (EVP) sea ice dynamics scheme into the Hadley Centre coupled ocean-atmosphere climate model HadCM3. Although the large-scale simulation of sea ice in HadCM3 is quite good with this model, the lack of a full dynamical model leads to errors in the detailed representation of sea ice and limits our confidence in its future predictions. We find that introducing the EVP scheme results in a worse initial simulation of the sea ice. This paper documents various enhancements made to improve the simulation, resulting in a sea ice simulation that is better than the original HadCM3 scheme overall. Importantly, it is more physically based and provides a more solid foundation for future development. We then consider the interannual variability of the sea ice in the new model and demonstrate improvements over the HadCM3 simulation.last_img read more

Natural growth rates in Antarctic krill (Euphausia superba): I. Improving methodology and predicting intermolt period

first_imgThe growth rates of postlarval krill (Euphausia superba) were measured across a wide range of environments in the Scotia Sea and around South Georgia using the Instantaneous Growth Rate (IGR) method. Each IGR experiment determined the intermolt period (IMP) and growth increment at molt (GI) of an average of 120 individuals incubated for 5 d in through-flowing ambient, filtered seawater. We examined the results from 51 IGR experiments involving 5,927 animals ranging between 25 mm and 62 mm. Animals were collected from an area that covered a latitudinal range of 108 and surface temperatures of between -0.85°C and 4.75°C. The measurement of IMP has rarely been achieved in IGR experiments because synchronous molting biases estimates. We overcame this by applying a binary logistic regression model to our data. This related IMP to temperature, body length, and maturity stage. Food did not influence IMP. Our model estimated that krill within our experiments had IMPs ranging from 9 d to 57 d. Temperature affected the IMP of females more than that of males. The IMPs of females were shortest around 2°C and increased at lower and higher temperatures. IMP increased with body size and altered according to gender, with male IMPs being 50% longer than those of equivalently sized females. One of the main assumptions of the IGR method is that the GI measured in the first few days reflects the in situ conditions experienced by krill in the previous intermolt period. However, we found that the GIs declined immediately and rapidly after capture, particularly when growth was initially high. Thus, conditions at time of molt also influence GI. We developed a method of correcting measured GIs to natural growth in field conditions. These refinements to IGR methodology (IMP and GI estimation) enable more accurate and precise predictions of krill growth rates in summer to be made.last_img read more

Substantial primary production in the land-remote region of the central and northern Scotia Sea

first_imgThe Scotia Sea area has high productivity relative to the Southern Ocean as a whole, but this displays strong latitudinal and longitudinal gradients. Elucidating the extent of these from a single cruise is problematic, given the high variability of bloom timing and location in this region. Therefore, this study used data from transects across the central Scotia Sea in spring, summer and autumn of 2006, 2008 and 2009, combined with satellite data, to obtain a larger-scale appreciation of the latitudinal contrasts in phytoplankton standing stock and primary production across the region. Concentrations of nitrate, phosphate and particularly silicic acid increased towards the south of the transect with the latter showing a step change at the Southern Antarctic Circumpolar Current Front (SACCF). Changes in seasonal nutrient concentrations indicated increasing phytoplankton uptake north of ∼57°S that peaked at ∼53°S in the Georgia Basin. Based on seasonal depletions of nitrate relative to phosphate, the highest relative nitrate uptake occurred northwest of South Georgia on the periphery of the Georgia Basin, indicating efficient nitrate use here due to iron-replete conditions. An integrative approach to examine these gradients was with the use of 10-year satellite climatology data. These showed that the lowest mean chlorophyll a (chl-a) values were in the central/northern Scotia Sea, but these were still substantial values, 67% of values within the Georgia Basin bloom. Cruise data on chl-a and on microplankton biomass from cell counts support this finding of substantial biomass in the central Scotia Sea; since these averaged half of values in the iron-fertilised bloom of the Georgia Basin downstream of South Georgia. Given that our transect was nearly 1000 km long and in parts was land remote with low iron concentrations, the relatively high production in the central and northern Scotia Sea is surprising. Iron levels may be maintained here by efficient recycling and irregular injections, possibly for example from dust deposition or shelf-derived inputs from the south. The moderate chl-a concentration across the mid-Scotia Sea and southwest of South Georgia reflect periodic, non-ice-associated blooms that occur in some years and not others. These may provide a connection between the large populations of krill inhabiting the northern and southern fringes of the Scotia Sea.last_img read more

The contribution of zooplankton faecal pellets to deep carbon transport in the Scotia Sea (Southern Ocean)

first_imgThe northern Scotia Sea contains the largest seasonal uptake of atmospheric carbon dioxide yet measured in the Southern Ocean. This study examines one of the main routes by which this carbon fluxes to the deep ocean, through the production of faecal pellets (FPs) by the zooplankton community. Deep sediment traps were deployed in two sites with contrasting ocean productivity regimes (P3, naturally iron-fertilized and P2, iron-limited), within the same water mass. The magnitude and seasonal pattern of particulate organic carbon (POC) and FPs in the traps was markedly different between the two sites. Maximum fluxes at P3 (22.91 mg C m−2 d−1; 2534 × 10 FP m−2 d−1) were an order of magnitude higher than at P2 (4.01 mg C m−2 d−1; 915 × 10 FP m−2 d−1), with flux at P3 exhibiting a double seasonal peak, compared to a single flatter peak at P2. The maximum contribution of FP carbon to the total amount of POC was twice as high at P3 (91%) compared to P2 (40%). The dominant FP category at P3 varied between round, ovoidal, cylindrical and tabular over the course of the year while, at P2, ovoidal FPs were consistently dominant, always making up more than 60% of the FP assemblage. There was also a difference in the FP state between the two sites, with FPs being relatively intact at P3, while FPs were often fragmented with broken peritrophic membranes at P2. The exception was ovoidal FPs, which were relatively intact at both sites. Our observations suggest that there was community shift from an herbivorous to an omnivorous diet from spring through to autumn at P3 while detritivores had a higher relative importance over the year at P2. Furthermore, the flux was mainly a product of the vertically migrating zooplankton community at P3 while the FP flux was more likely to be generated by deeper-dwelling zooplankton feeding on recycled material at P2. The results demonstrate that the feeding behavior and vertical distribution of the zooplankton community plays a critical role in controlling the magnitude of carbon export to the deep ocean in this region.last_img read more