1,721,097 research outputs found
High megabenthic abundance and diversity in deep fjords of the West Antarctic Peninsula: high sensitivity to climate change?
No full textHigh megabenthic abundance and species richness in deep fjords of the West Antarctic Peninsula: high sensitivity to climate change?
No full textPreliminary findings of the reproductive processes of deep water actinarians from the western Antarctic shelf
No full textSelective feeding by benthic foraminifera on labile phytodetritus on the western Antarctic Peninsula shelf (500m water depth): evidence from fatty acid biomarker analysis
No full textNovel method for generating high purity vortex modes
No full textA scheme for generating Laguerre-Gaussian vortex modes using a novel astigmatic mode converter based on spherical mirrors is described. A simple method for characterizing mode purity is employed to confirm the benefits of this scheme.</p
Reproductive biology of two species of holothurian from the deep-sea order Elasipoda, on the Antarctic continental shelf
No full textAntarctic shallow-water and deep-sea echinoderms are known to have seasonal gametogenic cycles linked to seasonal pulses of phytodetritus produced in surface waters. We suggest that phytodetritus reaching the Antarctic continental shelf may persist for longer timescales than in shallow OF deep waters as a result of the low temperatures, low flow velocities, and the relatively short descent. If this food source remains available for extended periods throughout the year, Antarctic continental shelf megabenthos may not entrain seasonal gametogenic periodicity.
To explore the reproductive response of the elpidiid holothurians, Protelpidia murrayi and Peniagone vignoni, a seasonal series of samples were taken on the West Antarctic Peninsula (WAP) at depths of 550-600 m between November 1999 and March 2001. Gonad indices were measured, and gonad tissues were analysed using histological and image analysis techniques. Oocyte size-frequency distributions were constructed from measurements of oocyte diameter, and analysed to describe reproductive patterns. Histological analyses of gonads tissue from P. murrayi suggest that gametogenesis is synchronised and seasonal, with spawning occurring between March and June. The onset of vitellogenesis appears to be initiated and synchronised by the arrival of the phytodetritus pulse. While, oocyte size-frequency distributions of P. vignoni suggest that oogenesis is synchronous between individuals, and infer a seasonal variation in gametogenic intensity, with an increase in production of vitellogenic oocytes that may be associated with an increase in food supply. The seasonal series of oocyte size-frequency distributions suggests that spawning commenced during October and November.
We propose that both P. murrayi and P. vignoni have opportunistic reproductive patterns. In P. murrayi, the distinct gametogenic response to the summer Antarctic-shelf food pulse may be well adapted to any trophic regime with a pulsed food supply. In contrast P. vignoni produces mature gametes all year round but capitalises on higher summer food flux by increasing the intensity of gamete production during this time. Therefore, although these species continue to feed during the austral winter and may gain sufficient energy to maintain basal metabolism and limited reproductive development, energetically more costly activities, such as high rates of vitellogenesis, may be reserved for the summer months when higher quality of food is available
Inter-annual variability and potential for selectivity in the diets of deep-water Antarctic echinoderms
No full textThe continental shelf of the West Antarctic Peninsula (WAP) is a highly productive region but also unusually deep as a result of isostatic depression by the polar ice cap. The close coupling of surface processes with those of the benthos would be expected in such a seasonally variable environment; however, the cold, deep conditions of the WAP shelf may allow for the persistence of organic material in the sediments as a “food bank”. Chlorophyll and carotenoid pigments were determined from the gut contents of seven species of echinoderm and from the surficial sediment on the bathyal continental shelf. Samples were collected as part of the FOODBANCS programme during successive cruises in austral spring (October 2000) and austral autumn (March 2001). Pigments were identified and quantified using reverse-phase high-performance liquid chromatography (HPLC). A lack of qualitative selectivity was observed among species, compared to that observed for deep-water assemblages at temperate latitudes, supporting the theory of a persistent “food bank”. However, significant quantitative differences were observed among species and between years and sampling location on the shelf. Species differences were marked between those we classified as “true” deposit feeders and those species whose diet also may be supplemented by scavenging and/or grazing
A large testate protist, Gromia sphaerica sp.nov. (Order Filosea), from the bathyal Arabian Sea
No full textThe deep ocean provides a habitat for several large testate protistan taxa, e.g., xenophyophores and komokiaceans. However, testate amoebae (orders Lobosea and Filosea) have never been reliably reported from below 270 m depth. Here we describe large spherical protists, up to almost 40 mm diameter, recovered in box core, multicore, and epibenthic sledge samples taken on the continental slope off Oman (NW Arabian Sea) during RRS Discovery Cruise 211. Specimens consist of an organic envelope, with numerous tiny apertures, enclosing a mass of fine waste pellets (stercomata). On the basis of its wall ultrastructure (revealed by high-voltage transmission electron microscopy), this organism is identified as a member of the filosean genus Gromia. It is described herein as Gromia sphaerica sp. nov. The wall is layered and includes the ‘honeycomb membrane', a structure that is unique to this genus. The new species is the first gromiid to be reported from the deep sea. It lives between about 1200 and 1630 m below the main oxygen minimum zone, in an area where bottom-water oxygen concentrations are around 0.47 ml l?1. The new gromiid species is clearly visible in bottom photographs taken at 1273 m (2.7 individuals m?2), 1318 m (2.7 indiv. m?2), 1624 m (17.3 indiv. m?2) and 1633 m (76.5 indiv. m?2). They lie partly embedded in the seafloor and are sometimes grouped in twos and threes. Specimens are typically surrounded by an apron of lighter-coloured sediment, possibly resulting from their feeding activities. Where they lie in very close proximity, the apron around one specimen typically obscures adjacent tests
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