Roberto Millán-Núñez

Protein, carbohydrate, lipid and chlorophyll a content in Isochrysis aff. galbana (clone T-Iso) cultured with a low cost alternative to the f/2 medium

Growth, proximate composition and chlorophyll a content was estimated in static cultures of Isochrysis aff. galbana (clone T-Iso) to compare the quality and quantity of the biomass produced with an agricultural fertilizer medium versus f/2 medium. Culture of microalgae was done with controlled temperature, air flux of 4.5 l min−1, salinity of 33‰ and an irradiance of 110±3 μmol m−2 s−1. Daily samples from the cultures were taken to estimate cellular density, proximate composition and chlorophyll a content during 7 days. Mean cellular density from samples with f/2 medium and with agricultural fertilizer were similar (no significance at P≤0.05), and mean growth rates of 0.62 and 0.61 doubling per day, respectively. Maximum similar values of protein content of 7.3 and 7.6 pg per cell were estimated on the 5th day in f/2 and agricultural fertilizer medium, respectively. Carbohydrate and lipid content decreased during the first 5 days corresponding to the exponential growth in both experiments. Higher content of carbohydrate (no significance at P≤0.05) was found in both media during the first 2 days, after 4 days the carbohydrates reduced three times theirs concentrations. Generally lipid contents in the cultures with agricultural fertilizer were significantly higher (P≤0.05) than f/2 medium. The chlorophyll a content increased exponentially during the culture, and its concentration was similar in both experiments. In conclusion, the cellular density and the biochemical constituents were similar when using either media. This fertilizer can be used in the production of I. galbana (T-Iso) employed in aquaculture.

Biomass production and nutrient uptake by Isochrysis aff. galbana (Clone T-ISO) cultured with a low cost alternative to the f/2 medium

Abstract Biomass production and uptake of nitrate, phosphate and ammonium were determined in batch culture of the marine microalgae Isochrysis aff. galbana (Clone T-ISO) for 7 days comparing an agricultural fertilizer media with the f/2 media. The average cellular density obtained with the f/2 media and the agricultural fertilizer showed no significant difference ( P >0.05) (average growth rate of 0.43 and 0.42 per day, respectively). During the first 4 days, the phosphate in the agricultural fertilizer media was consumed ten times faster than in the f/2 media. When nitrate and ammonium were added together, the ammonium was consumed eight times faster than the nitrate in a period of 5 days. Below concentrations of 1.36 μM of ammonium, nitrate began to be consumed. The nitrate uptake in the f/2 media increased substantially (to 555 μM) from the fourth to the seventh day of culture. The cost of the f/2 media is eight times more expensive than that prepared with agricultural fertilizer. We conclude that agricultural fertilizer did not have a negative effect compared to f/2 on the growth rate of I. aff. galbana (Clone T-ISO), produced the same amount of biomass as the f/2 media, and was much cheaper. The alternate media shows great potential for use in aquaculture for I. aff. galbana (Clone T-ISO) production.

Modeling the vertical distribution of chlorophyll in the California Current System

Remote sensing of ocean color provides data on the average photosynthetic pigment concentration in the first optical depth. To model primary productivity in the water column, estimates of the vertical distribution of pigment concentration are required. We used a Gaussian distribution function proposed by Platt et al. [1988] to represent the pigment vertical profile with four parameters. Empirical relationships were derived to estimate these parameters for the California Current System between 28° and 37°N, using California Cooperative Oceanic Fisheries Investigations (CalCOFI) data (1978–1992). The studied area was divided into six spatial subregions and temporally into warm and cool seasons. Regression models were developed for each subregion and season to estimate each of the parameters as functions of surface chlorophyll. Comparison of chlorophyll profiles obtained during the 1994 CalCOFI cruises (not used for constructing the models) with those estimated with our models shows a general agreement. Assuming a homogeneous biomass profile resulted in underestimation of integrated primary productivity (pp) by as much as 30%, whereas the modeled profiles gave equal or overestimated pp (up to 23%), with respect to the values derived from the real 1994 profiles.

Assessing dynamics micro-regions in the Great Islands of the Gulf of California based on MODIS aqua imagery products

The Great Islands zone, in the Gulf of California, presents high phytoplankton concentration as a result of the high Turbulent Kinetic Energy (TKE). In this work we looked for dynamics zones based on Empirical Orthogonal Function analysis (EOF). The input data were Sea Surface Temperature (SST) and Chlorophyll-a concentration (Chla) from daily MODIS-AQUA at 1 Km from 2003 to 2006. Time series were generated to define the average conditions for summer and winter spring tides. Results showed that in general and during summer-spring tides, higher Chla concentrations are localized in the west coast, with a displacement to the south. These high Chla were associated with tidal mixing. Zero EOF values in summer showed the boundary between low SST and high Chla. During winter-spring tides there were more spatial variability than during summer time. Zero EOF value in winter time showed low SST and Chla in the west coast due to stronger mixing conditions that stay longer. Results of this work emphasize that a dynamic regionalization can be used in high TKE areas and it helps to define zones with a similar response based on the input parameters chosen.

Bio-Optical Characteristics of the Northern Gulf of California during June 2008

Bio-optical variables in the Northern Gulf of California were analyzed using in situ and satellite data obtained during a cruise in June 2008. The study area was divided into three bio-optical regions: Upper Gulf (UG), Northern Gulf (NG), and Great Isles (GI). Each region was characterized according to phytoplankton pigment concentration, phytoplankton and nonpigmented material spectral absorption coefficients, and spectral reflectance. Observed patterns were an indication of the shift in bio-optical conditions from north to south going from turbid and eutrophic waters to mesotrophic ones. Although there was a good agreement between satellite and in situ Chla (RMSE ±33%), an overestimation of in situ Chla was observed. This was partly explained by the presence of nonalgal particles, as well as the influence of desert and continental aerosols, which is generally overcorrected in the standard processing. The UG and NG could be considered as Case  2 waters, but they did exhibit different bio-optical characteristics. This implies that both biological and optical properties should be invoked to better understand water reflectance variability in the study region and its implications for the remote sensing of Chla and biogeochemical processes.