Use of different commercial Artemia sp. Enrichements in Octopus Vulgaris, paralarval rearing at initial planctonic phase: effects on growth, survival and fatty acid composition of the paralarvae

[EN] Octopus "paralarvae", are planktonic, swim actively and have high metabolic rates, requiring large quantities of live prey of adequate motility and nutritional quality ( Iglesias et al., 2000; Navarro and Villanueva, 2000, 2003). During the planktonic phase, they undergo strong morphological changes, after which the octopuses start settling to the bottom. The potential of Octopus vulgaris as candiadate for diversification of marine aquacultures are mainly due to its high food conversion rate and fast growth.( Iglesias et al 2006). Despite the research effort taken until now, paralarval rearing of O. vulgaris still suffers high mortalities which limited the industrial culture of this species. The main problems in the paralarval rearing stages are the high mortality rates and poor growth. These are attributed to the lack of standardized culture techniques and nutritional deficiencies in the diet of paralarvae, especially in n-3 highly unsaturated fatty acids (n-3 HUFA). The objective if this experience was to test different commercial live prey enrichment to improve nutritional quality of the artemia.

Serum free testosterone, leptin and soluble leptin receptor changes in a 6-week strength-training programme

[EN] Strength training is usually associated with a reduction in fat mass and with muscle hypertrophy. The aim of the present study was to examine whether the serum free leptin index (FLI), measured by the molar excess of soluble leptin receptor (sOB-R) over leptin, is increased by 6 weeks of strength training. Eighteen male, physical education students were randomly assigned to two groups: a strength-training (n 12) and a control group (n 6). Body composition (lean body mass and body fat) determined by dual-energy X-ray absorptiometry (DXA), muscle performance and leptin, sOB-R, total testosterone and free testosterone concentrations were determined before and after training. Fat mass was reduced by 1 kg with strength training (P<0.05). Lean body mass of trained extremities was increased by 3% (P<0.05), while the concentration of free testosterone in serum was reduced by 17% (P<0.05) after training. However, despite the reduction in fat mass and free testosterone, serum leptin concentration was not significantly affected by strength training, even after accounting for the differences in body fat. By contrast, for a given fat mass, the sOB-R was increased by 13% (P<0.05) at the end of the strength-training programme, although the molar excess of sOB-R over leptin remained unchanged. Therefore, the quantity of free leptin available to bind to the target tissues was not significantly affected by the short strength-training programme, which elicited a 7% reduction in fat mass.

Phytoplankton community composition and size-abundance spectra in areas of the Alborán sea with different hydrological characteristics

[EN] Size-abundance spectra (SAS) were analyzed in different phytoplankton assemblages of the Alborán Sea collected in areas with contrasting hydrological features (upwelling areas and anticyclonic gyre). Abundance of micro-plankton cells decreased following the hydrological gradient from the most productive stations towards offshore stations. This size-fraction of phytoplankton was dominated by diatoms. Pico-plankton followed an opposite gradient. Concordantly, the slope of the SAS trended to decrease from coastal areas (upwelling) towards the anticyclonic gyre. However, phytoplankton assemblages featuring similar SAS values presented a quite different taxonomical composition of their diatom communities. According to the previous available information about the taxonomical composition of the phytoplankton communities in the Alborán Sea, these differences in diatom composition are indicative of differences in productivity of the phytoplankton. Consequently, the utility of phytoplankton SAS as an indicator of changes in the phytoplankton communities of the Alborán Sea is discussed.

Zooplankton oxygen consumption and nutrient release in relation to species composition, animals size and enviromental conditions in the Baltic Sea during May and August

[EN] Zooplankton metabolism in terms of oxygen consumption and ñutrient reléase (ammonia, phosphate) were measiu'ed in the Baltic Sea, a températe área with high envirormiental changes both in space and in time. Plankton of the surface layer were analysed with balance measurements in 4 size classes between 50 and 1000 nm during spring in 1988, 1990 and 1991, in summer 19^8 and 1990 as well. The use of electrón transport system (ETS), and the Glutamate Dehydrogenase (GDH) activity as indicators for respiration and ammonia reléase respectively, enlarged the data density and made a three dimensional resolution available (May 1990, 1991). Data are in the range of the latitudinal dependend magnitude. They reflect slight interannual, more seasonal and regional aspects. Animáis size, temperature, food concentration, and species composition influence the specific rates

A dynamic model of oceanic sulfur (DMOS) applied to the Sargasso Sea: Simulating the dimethylsulfide (DMS) summer paradox

[EN]A new one-dimensional model of DMSP/DMS dynamics (DMOS) is developed and applied to the Sargasso Sea in order to explain what drives the observed dimethylsulfide (DMS) summer paradox: a summer DMS concentration maximum concurrent with a minimum in the biomass of phytoplankton, the producers of the DMS precursor dimethylsulfoniopropionate (DMSP). Several mechanisms have been postulated to explain this mismatch: a succession in phytoplankton species composition towards higher relative abundances of DMSP producers in summer; inhibition of bacterial DMS consumption by ultraviolet radiation (UVR); and direct DMS production by phytoplankton due to UVR-induced oxidative stress. None of these hypothetical mechanisms, except for the first one, has been tested with a dynamic model. We have coupled a new sulfur cycle model that incorporates the latest knowledge on DMSP/DMS dynamics to a preexisting nitrogen/carbon-based ecological model that explicitly simulates the microbial-loop. This allows the role of bacteria in DMS production and consumption to be represented and quantified. The main improvements of DMOS with respect to previous DMSP/DMS models are the explicit inclusion of: solar-radiation inhibition of bacterial sulfur uptakes; DMS exudation by phytoplankton caused by solar-radiation-induced stress; and uptake of dissolved DMSP by phytoplankton. We have conducted a series of modeling experiments where some of the DMOS sulfur paths are turned “off” or “on,” and the results on chlorophyll-a, bacteria, DMS, and DMSP (particulate and dissolved) concentrations have been compared with climatological data of these same variables. The simulated rate of sulfur cycling processes are also compared with the scarce data available from previous works. All processes seem to play a role in driving DMS seasonality. Among them, however, solar-radiation-induced DMS exudation by phytoplankton stands out as the process without which the model is unable to produce realistic DMS simulations and reproduce the DMS summer paradox.