RESUMEN

To confirm the Habitat Compression Hypothesis, a cruise to the Eastern Tropical North Pacific (ETNP) took place at the entrance of the Gulf of California, in an area rarely studied at the southern limit of the California Current, where it mixes with waters of the West Mexican Current and the Gulf of California. No significant day-night differences in the vertical distribution (0-500 m depth) of zooplankton were found based on 22 MOCNESS tows and, for the first time, a 48-h cycle of stratified zooplankton sampling. Most zooplankton groups were observed within the upper 100 m, above the oxycline, with oxygen concentrations as low as 45 µmol kg-1. Some California Current-influenced samples showed a slightly different vertical distribution. A ∼50% reduction in the number and abundance of 24 zooplankton groups was recorded within the Oxygen Minimum Zone, from 100 to 500 m depth. Vertical migrator's exceptions include some euphausiid species that migrate into the OMZ during the day. Principal Component Analyses showed that the vertical distribution of zooplankton is limited by oxygen, with a low zooplankton carbon density below ∼100 m depth within the OMZ. The difference between day and night for the upper 0-100 m layer was non-significant (U221 = 57; p = 0.947); however, the data showed great variability. Thus, zooplankton Carbon remains relatively constant, in the upper 100 m, and is available during day and night, in the studied area.

Asunto(s)

Oxígeno , Zooplancton , Animales , Ecosistema , México

RESUMEN

Microbial communities play a central role in the N cycle of oceanic oxygen minimum zones (OMZs), such as in the Eastern Tropical North Pacific (ETNP). We explored the spatial distribution of the genetic potential for ammonia oxidation (amoA gene for bacteria and archaea), denitrification (nirS and nirK), anaerobic ammonium oxidation (anammox) (hzo) and dissimilarity nitrate reduction to ammonia (DNRA) (nrfA) and their relationships with the hydrological variables and isotopic composition of nitrate in the ETNP off Mexico. Oxygen concentration, the availability of N chemical forms and the upwelling shaped the distribution of N cycling genes along the water column. The high abundance of N genes and the isotopic composition of nitrate suggest the N cycling is very dynamic in the OMZ core. The accumulation of nitrite, the high abundance of archaeal amoA genes, and the deviation of the N and O isotopes of nitrate from the expected 1:1 ratio for nitrate reduction in the upper portion of this OMZ indicate that nitrification is a relevant process that fuels the denitrifier community. Conversely, the high abundances of nitrate, ammonium and nrfA genes in the deeper layer indicate that DNRA is a crucial process enhancing anammox there. These results show the need for more detailed studies of the N processes in OMZs.

Asunto(s)

Archaea/metabolismo , Bacterias/metabolismo , Nitrógeno/metabolismo , Oxígeno/metabolismo , Agua de Mar/microbiología , Compuestos de Amonio/metabolismo , Archaea/clasificación , Archaea/genética , Bacterias/clasificación , Bacterias/genética , Desnitrificación , México , Microbiota , Nitratos/metabolismo , Nitrificación , Nitritos/metabolismo , Océanos y Mares , Oxidación-Reducción

RESUMEN

This study investigated selected trace elements toxicity in sea turtles Caretta caretta population from Baja California Sur (BCS), Mexico, by analyzing associations among Zn, Se, Cu, As, Cd, Ni, Mn, Pb, and Hg with various biochemical parameters (packed cell volume, leukocytes, and selected blood parameters), and whether their concentrations could have an impact on the health status of sea turtles. Blood samples from 22 loggerhead (C. caretta) sea turtles from BCS, Mexico, were collected for trace elements on biochemistry parameter analyses. Significant associations among trace element levels and the biochemistry parameters were found: Cd vs ALP (R 2 = 0.874, p Ë‚ 0.001), As vs ALP (R 2 = 0.656, p Ë‚ 0.001), Mn vs ALP (R 2 = 0.834, p Ë‚ 0.001), and Ni vs LDH (R 2 = 0.587, p Ë‚ 0.001). This study is the first report of the biochemical parameters of the North Pacific loggerhead sea turtle (C. caretta) from Baja California Sur, Mexico, and it is the first to observe several associations with toxic and essential trace elements. Our study reinforces the usefulness of blood for the monitoring of the levels of contaminating elements and the results suggest that, based on the associations with health clinical parameters, high levels of Cd and As could be representing a risk to the North Pacific loggerhead population health.

Asunto(s)

Oligoelementos/sangre , Tortugas , Animales , Monitoreo del Ambiente , Mercurio , México

RESUMEN

The genus Balechina (=subgenus Pachydinium) was established for heterotrophic gymnodinioid dinoflagellates with a thick cell covering. The type species, B. pachydermata (=Gymnodinium pachyderm-atum), showed numerous fine longitudinal striae, whereas B. coerulea (=G. coeruleum) showed ~24 prominent longitudinal surface ridges or furrows and a distinctive blue pigmentation. We have investigated the morphology and molecular phylogeny of these taxa and the species Gymnodinium cucumis, G. lira and G. amphora from the western Mediterranean, Brazil and Japan. Sudden contractions at the cingulum level were seen in B. pachydermata, which also showed a high morphological variability which included morphotypes that have been described as Amphidinium vasculum, G. amphora, G. dogielii and G. gracile sensu Kofoid and Swezy. Molecular phylogeny based on small subunit rRNA gene sequences revealed that Balechina coerulea, G. cucumis and G. lira formed a clade distantly related to the clade of the type species, B. pachydermata, and G. amphora. We propose the new genus Cucumeridinium for the species with longitudinal ridges and a circular apical groove (Cucumeridinium coeruleum comb. nov., C. lira comb. nov. and C. cucumis comb. nov.), and Gymnodinium canus and G. costatum are considered synonyms of C. coeruleum. The genus Balechina remains for the species with a double-layer cell covering, bossed surface with fine striae, and an elongated elliptical apical groove. At present, the genus is monotypic containing only B. pachydermata.