1,721,115 research outputs found
Deep-sea exploration in the Indian Ocean
No full textAn article in BG East Africa's quaterly magazine describing fieldwork carried out offshore Tanzania by the SERPENT Project
Chondrocladia gigantea
No full textSessile organismThe giant clubsponge. A stalked demosponge found living on soft sediment at depths of 240-1600 m
Deep-water observation of scalloped hammerhead Sphyrna lewini in the western Indian Ocean off Tanzania
Full text linkA scalloped hammerhead Sphyrna lewini was observed opportunistically from a remotely operated vehicle 1 m off the seabed at 1042 m depth, during hydrocarbon exploration activities in the Ruvuma Basin off Tanzania. The observation, which occurred during night hours, is the deepest accurately recorded for this species and the first deep-water record for the Indian Ocean. The record adds support for the occurrence in deep water during night hours being a widespread and possibly common behaviour in this species, and further expands a small but growing literature that meso- and bathypelagic environments may be of greater importance to elasmobranchs previously considered to be primarily epipelagic
The physiological ecology of the specialist lagoon amphipod, Gammarus insensibilis
No full textCoastal lagoons are habitats of conservation importance. The characteristic fauna of lagoons includes a number of specialist species, some of which are scheduled for protection. Work on the conservation of coastal lagoons has suggested that detailed information on the ecology of lagoon specialist species is essential to ensure management strategies are relevant to the lagoonal species. This study addresses this issue by providing information about the monthly reproductive investment and energy-balance as well as interactions with parasites for the specialist lagoon amphipod, Gammarus insensibilis (Stock). For comparison information is also presented on the reproductive investment of the lagoonal isopod Idotea chelipes (Pallas). Gilkicker lagoon on the south coast of England, UK, from which the majority of samples were taken, demonstrated environmental variability characteristic of coastal lagoons. Annually, temperature varied between 2 and 28 °C and salinity fluctuated between extremes of 24 and 39. The Lymington-Keyhaven lagoons, also on the south coast of England, demonstrated similar variation. This has implications for Gammarus insensibilis, and effects on reproductive investment were evident. The amphipod was shown to employ a continuous reproductive strategy but while the overall investment, expressed as clutch volume, remained relatively stable over the course of the year, the individual components varied. In the summer, when weight-specific embryo number was at its highest with a mean of 13 embryos mg dry wt.-1 the mean size of the individual embryos was small (0.032 mm3). The opposite was true in the winter months, with mean brood sizes as low as 6 embryos mg dry wt.-1 while mean embryo volume was larger, at 0.04 mm3. Idotea chelipes demonstrated a more seasonal reproductive strategy in which winter reproductive output was low. The environmental variability also had effects on the metabolic rates of individual amphipods with temperature related increases in feeding and respiration rates in the summer months. Scope For Growth (SFG), a measure of net energy availability to the organism, was variable during the year and was unrelated to temperature and salinity. Lowest SFG occurred in spring in conjunction with peak reproductive output. This suggested that the amphipods were well adapted to the environmental variation of the lagoon and that it was reproductive investment that represented an important cost to the organism. Eighty four percent of G. insensibilis from Gilkicker were shown to be infected by microphallid trematode parasites. Reproductive investment was negatively affected, with a 36.6 % reduction in weight-specific brood size associated with higher degrees of infection. Respiration rates were also reduced in the infected organisms. The high prevalence of the parasites and the related effects on the host suggest that trematode infection should be considered, alongside the characteristic habitat variability, as an important aspect of the ecology of lagoons
Changes in deep-water epibenthic megafaunal assemblages in relation to seabed slope on the Nigerian margin
Full text linkLocal-scale habitat heterogeneity associated with changes in slope is a ubiquitous feature of bathyal continental margins. The response of deep-sea species to high habitat heterogeneity is poorly known and slope can be used as a proxy for many important ecological variables, such as current flow, sedimentation and substratum type. This study determines how slope angle effects megafaunal species density and diversity at the Usan field, offshore Nigeria, between 740 and 760 m depth. This deep-water area is increasingly exploited for hydrocarbons, yet lacking in baseline biological information. Replicated remotely operated vehicle video transect surveys were carried out using industry infrastructure (through the SERPENT Project) at a representative range of slopes (1°, 3°, 11° and 29°). Twenty-four species of benthic megafaunal invertebrate were found, numerically dominated by the echinoid Phormosoma placenta, and nine species of fish were observed. Megafaunal invertebrate deposit feeder density decreased significantly with increasing slope (density range 0.503–0.081 individuals m−2). Densities of megafaunal suspension feeders were very low except at the highest slope site (mean density 0.17 m−2). Overall species richness was greater on steeper slopes, although the richness of deposit feeders was not affected. Reduced labile organic matter in sediments on steeper slopes likely reduced deposit feeder densities, but increased current flow at higher slopes allowed both increased richness and density of suspension feeders
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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