José Eduardo Valdez-Holguín

Spatial distribution of chlorophyll α and primary productivity in relation to winter physical structure in the Gulf of California

The spatial distribution of chlorophyll α and productivity of phytoplankton and their relation with stratification was studied during winter of 1990 in the Gulf of California. According to the stratification parameter of the water column (Ф) we can distinguish three different zones during winter: one with strong turbulence (5<Ф<10 J m−3) close to the islands; the second zone with moderate turbulence (15<Φ<30 J m−3) in the central Gulf, and the third with high stratification (40<Ф<60 J m−3) in the southern Gulf. The lowest stratification was registered in the area near to Angel de la Guarda and Tiburon Islands, associated with low surface temperature (14–15°C), high surface chlorophyll a concentration (2.0–4.0 mg m 3) and low primary productivity (1.0–2.5 mgC m−3 h −1). Higher integrated values of chlorophyll a and primary productivity were measured in the central-southern area, related to moderate turbulence or stratification. Spring tides and wind stress appeared to be the principal physical factors for the high productivity in the central Gulf during winter. Moderate turbulence in the central-southern Gulf allows phytoplankton growth, however high turbulence in the area close to the large islands result in low primary productivity values.

Phytoplankton photosynthetic parameters from the Gulf of California southern region

Se determino la respuesta fisiologica del fitoplancton en la zona eufotica por medio de experimentos fotosintesis-irradiancia realizada de junio del 2000 a junio del 2001 en la Bahia de La Paz, Golfo de California, Mexico. Durante el periodo estratificado que comprende de junio a septiembre (indice de estratificacion > 200 J m-3) el numero de asimilacion (Pm) estuvo representado por un valor promedio de 3,7 mg C m-3 h-1, mientras que de noviembre a febrero, cuando la columna de agua fue homogenea (indice de estratificacion = 0 J m-3) fue de 9,2 mg C m-3 h-1. La eficiencia fotosintetica maxima a baja irradiancia (α) tuvo un valor promedio de 0,017 mg C m-3 h-1 (µmol cuanta m-2 s-1)-1 representativo del periodo estratificado, mientras que durante el periodo homogeneo fue de 0,063 mg C m-3 h-1 (µmol cuanta m-2 s-1)-1. Los parametros fotosinteticos (Pm y a) durante la mayor dinamica de la zona epipelagica evidencian la fotoaclimatacion del fitoplancton a la irradiancia promedio en la zona eufotica. Valores altos de Pm se relacionaron con la abundancia de diatomeas (Pseudo-nitzschia delicatissima, Chaetoceros compressus y Coscinodiscus perforatus), mientras que los valores menores de este parametro se asociaron con el grupo de los dinoflagelados. Los valores promedio estimados para el parametro de saturacion de luz (Ek) fueron 334, 173 y 91 µmol cuanta m-2 s-1 para superficie, 10 y 1% de la zona eufotica, respectivamente. De manera general, la comunidad fitoplanctonica estuvo dominada por nanofitoplancton (2-20 µm) durante todo el periodo considerado.

Fish assemblages in the bycatch of bottom shrimp trawls on the west side of the Gulf of California, Mexico

Abstract The assemblage of the fish species obtained as bycatch in trawl nets on the Gulf of California in 2004, 2005 and 2007 was studied. Sampling was carried out during July and August at a series of stations along the coast of Sonora. The criteria for the most important fish species caught were drawn from abundance and frequency of occurrence and weight, using various ecological indices (index of relative abundance, biological value index and index of relative importance). After identification, these species and their abundances were used to define study groups based on similarity matrices and Wards clustering method. We analysed 125 fish hauls containing>19,000 organisms, representing 243 species (fish, crustaceans, molluscs and echinoderms). There were 28 dominant species, most notably Urobatis halleri, Synodus scituliceps, Eucinostomus argenteus, Diplectrum pacificum and Haemulopsis nitidus. Cluster analysis, based on latitude, and bathymetry showed three station groupings. The first was characterized by species from the northern region of the Gulf with a bathymetric distribution>25 m. The second was dominated by species from the central to southern region from depths<25 m. The third was a transitional group with species found between the central and southern Gulf from depths of 10 to 45 m. Most fish assemblages consist of species with wide distribution within distinct biogeographic provinces, which showed a major change in the association, frequency and absence of species from north to south, indicating a variety of habitats in the Gulf of California.

Navicula sp. Sulfated Polysaccharide Gels Induced by Fe(III): Rheology and Microstructure

A sulfated polysaccharide extracted from Navicula sp. presented a yield of 4.4 (% w/w dry biomass basis). Analysis of the polysaccharide using gas chromatography showed that this polysaccharide contained glucose (29%), galactose (21%), rhamnose (10%), xylose (5%) and mannose (4%). This polysaccharide presented an average molecular weight of 107 kDa. Scanning electron microscopy (SEM) micrographs showed that the lyophilized Navicula sp. polysaccharide is an amorphous solid with particles of irregular shapes and sharp angles. The polysaccharide at 1% (w/v) solution in water formed gels in the presence of 0.4% (w/v) FeCl3, showing elastic and viscous moduli of 1 and 0.7 Pa, respectively. SEM analysis performed on the lyophilized gel showed a compact pore structure, with a pore size of approximately 150 nm. Very few studies on the gelation of sulfated polysaccharides using trivalent ions exist in the literature, and, to the best of our knowledge, this study is the first to describe the gelation of sulfated polysaccharides extracted from Navicula sp.

Environmental Variability and Oceanographic Dynamics of the Central and Southern Coastal Zone of Sonora in the Gulf of California

This study analyzed monthly and inter-annual variability of mesoscale phenomena, including the El Nino Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO) climate indexes and wind intensity considering their influence on sea surface temperature (SST) and chlorophyll a (Chl-a). These analyses were performed to determine the effects, if any, of climate indexes and oceanographic and environmental variability on the central and southern coastal ecosystem of Sonora in the Gulf of California (GC). Monthly satellite images of SST (°C) and Chl-a concentration were used with a 1-km resolution for oceanographic and environmental description, as well as monthly data of the climate indexes and wind intensity from 2002–2015. Significant differences (p > 0.05) were observed while analyzing the monthly variability results of mesoscale phenomena, SST and Chl-a, where the greatest percentage of anti-cyclonic gyres and filaments was correlated with a greater Chl-a concentration in the area of study, low temperatures and, thus, greater productivity. Moreover, the greatest percentage of intrusion was correlated with the increase in temperature and cyclonic gyres and a strong decrease of Chl-a concentration values, causing oligotrophic conditions in the ecosystem and a decrease in upwelling and filament occurrence. As for the analysis of the interannual variability of mesoscales phenomena, SST, Chl-a and winds, the variability between years was not significant (p > 0.05), so no correlation was observed between variabilities or phenomena. The results of the monthly analyses of climate indexes, environmental variables and wind intensity did not show significant differences for the ENSO and PDO indexes (p > 0.05). Nonetheless, an important correlation could be observed between the months of negative anomalies of the ENSO with high Chl-a concentration values and intense winds, as well as with low SST values. The months with positive ENSO anomalies were correlated with high SST values, low Chl-a concentration and moderate winds. Significant inter-annual differences were observed for climate indexes where the years with high SST values were related to the greatest positive anomaly of ENSO, of which 2002 and 2009 stood out, characterized as moderate Nino years, and 2015 as a strong El Nino year. The years with the negative ENSO anomaly were related to the years of lower SST values, of which 2007–2008 and 2010–2011 stood out, characterized as moderate Ninas. Thus, variability associated with mesoscale oceanographic phenomena and seasonal and inter-annual variations of climate indexes had a great influence on the environmental conditions of the coastal ecosystem of Sonora in the Gulf of California.

Sea Surface Temperature (SST) Variability of the Eastern Coastal Zone of the Gulf of California

The coastal zones are areas with a high flow of energy and materials where diverse ecosystems are developed. The study of coastal oceanography is important to understand the variability of these ecosystems and determine their role in biogeochemical cycles and climate change. Sea surface temperature (SST) analysis is indispensable for the characterization of physical and biological processes, and it is affected by processes at diverse timescales. The purpose of this work is to analyze the oceanographic variability of the Eastern Coastal Zone of the Gulf of California through the study of the SST from time series analysis of monthly data obtained from remote sensors (AVHRR-Pathfinder Version 5.1 and Version 5 resolution of 4 km, MODIS-Aqua, resolution of 4 km) for the period 1981 to 2016. The descriptive analysis of SST series showed that the values decrease from south to north, as well as the amplitude of the warm period decrease from south to north (cold period increase from south to north). The minimum values occurred during January and February, and ranged between 18 and 20 ◦C; and maximum values, of about 32 ◦C, arose in August and September. Cluster analysis allowed to group the data in four regions (south, center, midriff islands and north), the spectral analysis in each region showed frequencies of variation in scales: Annual (the main), seasonal, semiannual, and interannual. The latter is associated with the El Niño and La Niña climatological phenomena.