Sergio Aguíñiga García

Stable isotopes on jumbo squid (Dosidicus gigas) beaks to esitmate its trophic positon: comparison between stomach contents and stable isotopes

Stomach contents and carbon (C) and nitrogen (N) stable isotope analysis were used to evaluate trophic relationships of jumbo squid, Dosidicus gigas . Buccal masses, beaks and stomach contents of large and medium maturing-sized jumbo squid and muscle from its main prey, the myctophid Benthosema panamense , were collected in the Gulf of California, Mexico during 1996, 1997 and 1999. Both the quantified C and N-isotope ratios in muscle, and stomach content analysis revealed that larger-sized maturing squid showed a higher trophic position than medium-sized individuals. However, a discrepancy between stomach contents versus stable isotope analyses was found in evaluating trophic relationships. Simple dilution models as a function of growth were used to estimate the C and N renewal dietary shift for jumbo squid. Estimates of the initial C and N pools in D. gigas with an initial age of 70 days and 210 days indicated isotopic shifts of 32% after a threefold biomass increase and 25% after a fourfold biomass increase, respectively. Additionally, beak samples of jumbo squid were evaluated as an alternative tissue to estimate squid trophic position using stable isotopes. The results showed a significant correlation between stable isotope ratios from muscle and beak samples. Muscle isotope values were higher than beak by 1% and 4% for δ 13 C and δ 15 N respectively. A test with jumbo squid beaks collected from a stomach of a stranded sperm whale confirmed the viability of this method.

Seasonal and Spatial Variation of Carbon and Nitrogen Stable Isotopes in Mangrove Oysters (Crassostrea corteziensis) from the Northwest Coast of Mexico

ABSTRACT The aim of this study was to evaluate how Crassostrea corteziensis interacts with its habitat (abiotic factors) and to examine the isotopic variations that may exist over different scales of space and time at a subtropical gradient. This information will contribute to the work required to understand the ecology of this oyster species. We analyzed stable isotopes (&dgr;13C and &dgr;15N) in oyster soft tissue and the concentrations of chlorophyll a, NH4 +, and NO3 - in the waters of 6 lagoons during the dry and rainy seasons of 2008 and 2009. The mean C:N ratios in soft tissue were generally greater than 3.5 in the different lagoons and during both seasons, indicating a relatively high amount of lipids in the soft tissue related to reproductive activity. The isotopic variability between sites in this study (-25.5 to — 17.1‰ for &dgr;13C and 6.5 to 13.7‰ for &dgr;15N) suggested differences in the composition of suspended organic matter in the diet of this species at different locations, showing an opportunistic behavior that allowed us to detect differences on temporal and spatial scales. On a temporal scale, however, there was no difference in &dgr;13C, which was most likely related to the high food availability and the observation that individuals tend to feed on and share the same overabundant prey. In the case of &dgr;15N, significant temporal differences were evident in only a few lagoons. These differences were related to a differential contribution of NH4 + and NO3 - as primary sources to the suspended organic matter pool during the 2 seasons. On a spatial scale, some lagoons showed significant differences (P < 0.05) and high &dgr;15N values (>10‰) in addition to high concentrations of NH4 +. Enriched &dgr;15N values are often associated with an anthropogenic impact, as human and animal waste nitrate have &dgr;15N values of approximately 10–20‰.

Ultrafiltración de Caldos de Fermentación

Resumen Se estudio la microfiltracion tangencial y ultrafiltracion para concentrar caldos de levadura de Phaffia rhodozyma , la que es empleada para la produccion del colorante astaxantina. Se emplearon cartuchos de microfiltracion y ultrafiltracion para evaluar el efecto de las variables de operacion sobre el flujo de permeado. Se trabajo con presiones transmembrana de 35 a 210 kPa, flujos de alimentacion de 7 a 30 x10 -6 m 3 /s, pH de 4 a 8, y temperatura de 303 a 323 K. El flujo mas alto alcanzado en la microfiltracion fue de 13 x10 -6 m/s, observandose la disminucion de este si el pH aumenta; mientras que para la ultrafiltracion el flujo mas alto fue de 17 x10 -6 m/s. En ambos casos la concentracion de levadura maxima alcanzada fue de 250 kg/m 3 . Los resultados obtenidos muestran que la concentracion de caldos de fermentacion de Phaffia rhodozyma puede llevarse a cabo tanto por microfiltracion tangencial como por ultrafiltracion. Palabras claves: microfiltracion, ultrafiltracion, levadura, Phaffia rhodozyma, fermentacion