Selección del alimento en la hormiga argentina, Linepithema humile (Mayr, 1868) Hymenoptera, Formicidae)

Asignatura: Etología de los recursos pesqueros (Licenciatura Ciencias del Mar)

Preferencia de alimento del erizo cachero "Arbacia lixula" (Echinodermata: Arbacidae) ante una dieta basada en dos macroalgas.

Se estudió la preferencia de alimento del erizo cachero (Arbacia lixula) al administrarle una dieta basada en dos macroalgas (Ulva sp. y Cystoceira humilis). Los erizos muestran una tendencia clara a consumir mayor cantidad del alga verde frente al alga parda.ABSTRACT The food preferences of the black sea urchin (Arbacia lixula) was studied giving it a diet based on two macroalgae (Ulva sp. and Cystoceira humilis). The sea urchins showed a clear tendency to consume a higher quantity of green algae against brown algae.

Estudio de la selección por el color del alimento en la tortuga boba Caretta caretta tras la eclosión

The behavior of newborn pups of loggerhead turtles (Caretta caretta) towards a potential food after hatching and before eating food for the first time was studied. There was no significant time trend approach and bite of potentially edible objects based on their color or size. However, a clear trend was observed for those objects that are transparent, white or red, independently the sex of the animal. Furthermore, it was verified that the turtles do not have a biting behavior to feed from first contact with water, but it comes after 3 or 4 days. There is also a learning process that determines the choice of targets of further attacks.

Contribución a la recuperación y normalización de un alimento tradicional canario: chorizo de Teror. Evaluación de riesgos

[ES] Se plantea este estudio sobre el chorizo rojo de Teror, debido a la falta total y absoluta de definición de este alimento tradicional. Muchos elaboradores comercializan este alimento sin un referente de calidad y seguridad alimentaria básico, existiendo la necesidad de ofertar un producto de calidad contrastada al consumidor canario que demanda alimentos tradicionales para incorporar a su dieta. Por ello, se ha estudiado el proceso de elaboración, la evolución de los parámetros químicos y los parámetros de estabilidad (aw y pH), así como de los principales grupos microbianos presentes en dicho producto y la evaluación de los posibles riesgos asociados a la formulación de aditivos.

Krill excretion boosts microbial activity in the Southern Ocean

[EN]Antarctic krill are known to release large amounts of inorganic and organic nutrients to the water column. Here we test the role of krill excretion of dissolved products in stimulating heterotrophic bacteria on the basis of three experiments where ammonium and organic excretory products released by krill were added to bacterial assemblages, free of grazers. Our results demonstrate that the addition of krill excretion products (but not of ammonium alone), at levels expected in krill swarms, greatly stimulates bacteria resulting in an order-of-magnitude increase in growth and production. Furthermore, they suggest that bacterial growth rate in the Southern Ocean is suppressed well below their potential by resource limitation. Enhanced bacterial activity in the presence of krill, which are major sources of DOC in the Southern Ocean, would further increase recycling processes associated with krill activity, resulting in highly efficient krill-bacterial recycling that should be conducive to stimulating periods of high primary productivity in the Southern Ocean.

Krill as a central node for iron cycling in the Southern Ocean

[EN] In order to establish the potential role of Antarctic krill (Euphausia superba) in the recycling of bioactive elements, we have quantified the release of iron, phosphate, and ammonia by these organisms along the Antarctic Peninsula sector of the Southern Ocean. The experimental results suggested that the presence of krill has a significant impact on ambient iron concentrations, as large amounts of this trace element were released by the krill (22–689 nmol Fe g Dry Weight−1 h−1, equivalent to 0.2 to 4.3 nmol Fe L−1 d−1). Half of this iron release occurred within the first hour of the experiment, and differences in iron and phosphate release rates (3.1 to 14.0 μmol PO43− g DW−1 h−1) seemed to reflect differences in food availability. These results identify krill as a major node in iron cycling in the Southern Ocean, potentially influencing iron residence time in the upper water column of this region.

Caratterizzazione della microflora spontanea di un alimento fermentato vegano

Tra i prodotti vegani più richiesti vi sono i “formaggi” vegani, alimenti fermentati a base di frutta secca o ottenuti attraverso trattamenti su latte di mandorla e latte di soia, e successivamente fermentati. Nella mia attività ho caratterizzato un alimento fermentato vegano e studiato la successione microbica durante la fermentazione di un “formaggio” ottenuto partendo da anacardi e preparato in maniera artigianale. Oltre agli aspetti microbiologici, ho analizzato anche alcune caratteristiche fisico chimiche. Durante il processo di produzione gli anacardi vengono messi in ammollo per 8 ore a temperatura ambiente e, successivamente, i semi vengono scolati e risciacquati sotto acqua corrente. Gli anacardi vengono poi addizionati di acqua e microrganismi probiotici e tritati in un mixer fino al raggiungimento di una crema omogenea. A questo punto il prodotto viene lasciato riposare a temperatura ambiente per 48 ore durante le quali ha luogo la fermentazione e poi addizionato di ingredienti. Le indagini chimico fisiche effettuate hanno evidenziato che il pH si mostra già basso prima dell’inizio della fermentazione vera e propria e scende a 4.5 dopo 48 ore di riposo a causa dell’accumulo di acidi organici, ed in particolare di acido lattico e acetico che indicando un’attività fermentativa condotta dai batteri lattici. Le analisi microbiologiche hanno confermato che l’effettivo agente di fermentazione era costituito da questi batteri che sono stati identificati a livello molecolare. Le specie identificate due eterofermentanti (Weissella e Leuconostoc), presenti soprattutto nelle prime fasi della fermentazione, ed una omofermentante (Pediococcus), prende il sopravvento mano a mano che la fermentazione procede. Il lavoro svolto ha permesso di ottenere alcune importanti informazioni per la produzione industriale di un “formaggio” vegano fermentato. Il processo studiato presenta numerosi punti di rischio che devono essere presi in considerazione prima di poter giungere alla messa a punto di un prodotto definitivo.

Alimento con alto contenido de fructanos

El topinambur (Helianthus tuberosus L.) es una especie perteneciente a la familia de las Asteráceas originaria de América del Norte. Esta especie produce tallos subterráneos (tubérculos) que almacenan polisacáridos en forma de fructanos y, dentro de éstos, la inulina es el principal carbohidrato de reserva. Este compuesto posee características beneficiosas en la salud al actuar como fibra dietaria, sin disminuir la absorción de minerales. La presencia de inulina y sus derivados, hace de los tubérculos una buena fuente de fibra dietaria y particularmente de fibra funcional, cuya definición comprende a aquellos carbohidratos no digeribles aislados que tienen efectos fisiológicos beneficiosos en los seres humanos. Los objetivos de este estudio fueron: o Elaborar puré de alto contenido de fructanos, con variantes, a partir de tubérculos de topinambur de variedades Roja y Blanca; o Caracterizar de forma físico-química los tubérculos sin procesar y los purés elaborados; o Cuantificar el contenido de fructanos presente en los tubérculos sin procesar y en los productos obtenidos luego de cada elaboración; o Evaluar la aceptación por parte de los consumidores del puré preparado, mediante una prueba de evaluación sensorial. Siguiendo los objetivos, se elaboraron los purés, realizaron las caracterizaciones físico-químicas y cuantificaciones de fructanos en los tubérculos y productos obtenidos, y se sometió el preparado a una prueba sensorial afectiva con escala hedónica. Los resultados obtenidos indican que el procesamiento de tubérculos de topinambur para obtener puré, no modifica sustancialmente el contenido de fructanos, y las pérdidas asociadas al mismo varían entre el 0% y el 16% dependiendo del ensayo. Los consumidores aceptarían comprar el producto evaluado, si se ofreciera en el mercado a igual costo que un puré de papas tradicional, y no exhiben preferencia de una variedad de topinambur sobre la otra en los productos preparados. Por ello resulta viable elaborar puré de topinambur de variedad Roja o Blanca, el cual se considera beneficioso para la salud por su alto contenido en fructanos, cuyo valor mínimo cuantificado fue de 7,4% en el producto preparado, considerando que el mismo sería aceptado por la población.

Gene expression and physiological changes of the Antarctic krill Euphausia superba under different hypoxia intensities

Antarctic krill (Euphausia superba) from South Georgia comprise one of the most northern and abundant krill stocks. South Georgia waters are undergoing rapid warming, as a result of climate change, which in turn could alter the oxygen concentration of the water. We investigated gene expression in Antarctic krill related to aerobic metabolism, antioxidant defence, and heat-shock response under severe (2.5% O2 saturation or 0.6 kPa) and threshold (20% O2 saturation or 4 kPa) hypoxia exposure compared to in situ levels (normoxic; 100% O2 saturation or 21 kPa). Biochemical metabolic and oxidative stress indicators complemented the genic expression analysis to detect in vivo signs of stress during the hypoxia treatments. Expression levels of the genes citrate synthase (CS), mitochondrial manganese superoxide dismutase (SODMn-m) and one heat-shock protein isoform (E) were higher in euphausiids incubated 6 h at 20% O2 saturation than in animals exposed to control (normoxic) conditions. All biochemical antioxidant defence parameters remained unchanged among treatments. Levels of lipid peroxidation were raised after 6 h of severe hypoxia. Overall, short-term exposure to hypoxia altered mitochondrial metabolic and antioxidant capacity, but did not induce anaerobic metabolism. Antarctic krill are swarming organisms and may experience short periods of hypoxia when present in dense swarms. A future, warmer Southern ocean, where oxygen saturation levels are decreased, may result in smaller, less dense swarms as they act to avoid greater levels of hypoxia.

Whale sightings, group sizes and krill biomass in West Greenland in 2005

This study combined data on fin whale Balaenoptera physalus, humpback whale Megaptera novaeangliae, minke whale B. acutorostrata, and sei whale B. borealis sightings from large-scale visual aerial and ship-based surveys (248 and 157 sightings, respectively) with synoptic acoustic sampling of krill Meganyctiphanes norvegica and Thysanoessa sp. abundance in September 2005 in West Greenland to examine the relationships between whales and their prey. Krill densities were obtained by converting relationships of volume backscattering strengths at multiple frequencies to a numerical density using an estimate of krill target strength. Krill data were vertically integrated in 25 m depth bins between 0 and 300 m to obtain water column biomass (g/m**2) and translated to density surfaces using ordinary kriging. Standard regression models (Generalized Additive Modeling, GAM, and Generalized Linear Modeling, GLM) were developed to identify important explanatory variables relating the presence, absence, and density of large whales to the physical and biological environment and different survey platforms. Large baleen whales were concentrated in 3 focal areas: (1) the northern edge of Lille Hellefiske bank between 65 and 67°N, (2) north of Paamiut at 63°N, and (3) in South Greenland between 60 and 61° N. There was a bimodal pattern of mean krill density between depths, with one peak between 50 and 75 m (mean 0.75 g/m**2, SD 2.74) and another between 225 and 275 m (mean 1.2 to 1.3 g/m**2, SD 23 to 19). Water column krill biomass was 3 times higher in South Greenland than at any other site along the coast. Total depth-integrated krill biomass was 1.3 x 10**9 (CV 0.11). Models indicated the most important parameter in predicting large baleen whale presence was integrated krill abundance, although this relationship was only significant for sightings obtained on the ship survey. This suggests that a high degree of spatio-temporal synchrony in observations is necessary for quantifying predator-prey relationships. Krill biomass was most predictive of whale presence at depths >150 m, suggesting a threshold depth below which it is energetically optimal for baleen whales to forage on krill in West Greenland.

(Table 1) Krill (Euphausia superba) biomass estimates at South Georgia Island from 2001-2005

The South Georgia region supports a large biomass of krill that is subject to high interannual variability. The apparent lack of a locally self-maintaining krill population at South Georgia means that understanding the mechanism underlying these observed population characteristics is essential to successful ecosystem-based management of krill fishery in the region. Krill acoustic-density data from surveys conducted in the early, middle and late period of the summers of 2001 to 2005, together with krill population size structure over the same period from predator diet data, were used with a krill population dynamics model to evaluate potential mechanisms behind the observed changes in krill biomass. Krill abundance was highest during the middle of the summer in 3 years and in the late period in 2 years; in the latter there was evidence that krill recruitment was delayed by several months. A model scenario that included empirically derived estimates of both the magnitude and timing of recruitment in each year showed the greatest correlation with the acoustic series. The results are consistent with a krill population with allochthonous recruitment entering a retained adult population; i.e. oceanic transport of adult krill does not appear to be the major factor determining the dynamics of the adult population. The results highlight the importance of the timing of recruitment, especially where this could introduce a mismatch between the peak of krill abundance and the peak demand from predators, which may exacerbate the effects of changes in krill populations arising from commercial harvesting and/or climate change.