Oxygen minimum zones (OMZs) are important sources of CO 2 to the atmosphere when physical forces bring subsurface water with high dissolved inorganic carbon (DIC) to the surface. This study examines, for the first time, the influence of the OMZ of the coastal North Eastern Tropical Pacific off Mexico on surface CO 2 fluxes. We use variations in the oxycline depth and subsurface water masses to discern physical oceanographic influences. During two cruises, in November 2009 and August 2010, DIC and total alkalinity (TA) measurements were used to estimate pCO 2 and air-sea CO 2 fluxes. At the OMZ layer, Subtropical Subsurface Water (StSsW) was found to have high pCO 2 values (1290 6 70 latm). Due to strong vertical stratification, however, the relationship between DpCO 2 at the air-sea interface and the oxycline/StSsW upper limit depth was weak. During November, the region was a weak source of CO 2 to the atmosphere (up to 2.5 mmol C m ) prevented subsurface mixing of water from the OMZ to the upper layer; particularly in November 2009 which was during an El Niño event. Results suggest that advection of surface water masses, reinforced by strong vertical stratification, controlled surface pCO 2 , and air-sea CO 2 fluxes.

The physiological responses of the coral Pocillopora capitata to environmental conditions common in winter and summer were studied in 2007 during February–March (winter) and June–July (summer) at La Boquita reef (Manzanillo, Colima, Mexico). Shallow and deep sampling stations were established at different distances from a small jetty built next to the Juluapan Lagoon. We analyzed superoxide radicals () and lipid peroxidants (TBARS); the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione‐S‐transferase (GST); chlorophyll a (Chl a), zooxanthellae density (ZD); and mycosporine‐like amino acids (MAAs). Our results showed that the , TBARS, CAT, GST, MAAs, and Chl a, levels were significantly higher in summer (P < 0.05); no seasonal difference was found for GPx, GR or ZD. We found significant differences (P < 0.05) in winter only for Chl a and ZD at shallow sites and, in contrast, for at deeper sites. The results of this study indicate that increasing temperature and radiation associated with seasonal changes (from winter to summer), the efficiency of the enzymes GST, CR and GPX, and the production of MAAs together form a powerful mechanism for P. capitata to offset the detrimental effects of environmental change.

The ocean off the Baja California Peninsula (Mexico) has been affected by interannual processes. Some of these processes have produced changes in oceanic circulation and the atmosphere, which have been reflected in the structure of the water column. Stratification, defined as the amount of energy needed to mix water throughout the water column, determines nutrient availability in the euphotic zone for phytoplankton growth. The aim of this study is to describe and relate the interannual variations of phytoplankton production and biomass with changes in the structure of the water column. To this end, we analyzed time series (1997-2016) for integrated Chlorophyll a, integrated primary production, pycnocline depth, mixed layer depth, and stratification indices along line 100 of the Investigaciones Mexicanas de la Corriente de California (IMECOCAL) program. The results showed 2 periods of high stratification and a decrease in phytoplankton production and biomass off Baja California, corresponding to the intrusion of subarctic water and El Niño 2015-2016. Finally, by using generalized additive models, we related 2 photosynthethic parameters-maximum photosynthetic rate and maximum light utilization coefficient-with water stratification. These relationships explained interannual variations in phytoplankton production in terms of water column stratification. The time series and the analysis reported here for IMECOCAL line 100 could be used to extrapolate the effects of interannual physical processes on phytoplankton in other zones off the Baja California peninsula.

A partir de las propiedades bio-ópticas, los coeficientes de absorción por partículas, detritos y fitoplancton (a p , a dT , a φ) se evaluó el efecto de los vientos Santa Ana en el océano frente a Baja California ocurridos durante octubre de 1999. Los vientos medidos en la estación meteorológica frente a la Bahía de Todos Santos y los determinados a partir de información de satélite indicaron tres eventos Santa Ana, caracterizados por baja humedad relativa, alta temperatura del aire y vientos con dirección predominante del este-noreste. Los valores del coeficiente de absorción de detritos (a dT) fueron hasta diez veces mayores en las muestras superficiales de octubre, con relación a las de enero, abril y agosto de 1999. Los altos valores de a dT se debieron al material inorgánico aero-transportado por los vientos tierra-mar ocurridos del 9 al 11 y del 17 al 20 de octubre. Los coeficientes de absorción de las particulas (a p) y el fitoplancton (a φ) en la zona eufótica fueron mayores en abril, como resultado de la abundancia del fitoplancton. Los valores de a p , a φ y K d para la zona eufótica fueron ajustados a una función de potencia con la clorofila como variable independiente, con una variancia explicada de 37%, 72% y 16%, respectivamente. Cuando se excluyeron del ajuste los valores de a dT medidos en la superficie durante octubre, la clorofila explicó 82% de la variabilidad en los coeficientes de absorción (a p y a φ) y 87% en K d. A partir de la ecuación que relaciona la reflectancia de la radiancia espectral ascendente (R rs) con la clorofila, se determinó que ~80% de la variabilidad en la clorofila superficial es explicada por la razón de reflectancia R rs(443) /R rs(555) medida en la zona de estudio. Las estimaciones regionales de clorofila a partir de información bioóptica obtenida en la columna de agua no fueron afectadas fuertemente por el polvo aero-transportado durante los vientos Santa Ana ocurridos en octubre de 1999.

The response of primary producers to seasonal and interannual variabilities in the hydrographic conditions observed between 1997 and 2012 is analyzed for the southern portion of the California Current System (CCS). The analysis uses the optimum rate of primary productivity (PP) normalized by units of chlorophyll (Chla) in the water column () and Chla concentration. In situ PP estimations using the 14 C method were obtained as part of the seasonal cruises conducted by the Investigaciones Mexicanas de la Corriente de California program. Supplementary data included sea surface temperature (SST) as measured by the AVHRR sensor from 1985-2009. We found the mean value of to be at 5.1 ± 3.3 mg C•(mg Chla)-1 •h-1 , with maximum ranges of 0.5 and 17.5 mg C•(mg Chla)-1 •h-1. The relationship between and SST suggested a phytoplankton community change at around 19 ºC, which characterized the transitional nature of the southern portion of the CCS. SST data suggested, on the one hand, that on average the 19 ºC isotherm is located in the vicinity of Punta Eugenia and, on the other, that its spatial variability defined the alternating cool-warm conditions. At the seasonal scale, this isotherm showed a marked latitudinal displacement (from 24ºN to 32ºN), which was observed to be even out of this range during interannual events associated with El Niño/La Niña. Under both cool-warm hydrographic conditions, the phytoplanktonic community showed large rates (~6 mg C•(mg Chla)-1 •h-1). At the interannual scale, changes were associated to changes in the abundance and composition of nano-microphytoplankton. Additionally, data suggested that high PP rates during warm periods could be attributed to an enhanced picoplankton contribution.

Abstract.-Temporal variability of hydrographic data, nutrients, phytoplankton chlorophyll a, and rate of primary production for the Cuyutlan Lagoon (CL) were analyzed. Surface temperature had a seasonal pattern, lower in December and higher by July and October. Lowest salinity values were observed in October associated to the raining season, which created estuarine features inside the lagoon. Nutrient concentrations ( ) increased in February and June as result of organic matter remineralization, with higher silicate concentrations by October because freshwater run-off influence into the lagoon. During the other months dissolved silicate increase due to biogenic silica dissolution. Using the Redfield ratio as a stoichiometric nutrient balance criterion, phosphate deficits were observed in CL due to phytoplankton nutrient uptake. Chlorophyll a increased above 2.0 mg m -3 as result of rich-nutrient water, producing an elevated phytoplankton biomass. Average phytoplankton production was 1.26 g C m -3 d -1 , indicating that Cuyutlan Lagoon is ∼40% more productive related to other subtropical and temperate coastal lagoons. With chlorophyll a concentration as criteria to define trophic levels, CL could be described as a eutrophic ecosystem. Physical variables, dissolved inorganic nutrients, and chlorophyll a exhibited temporal variability in the lagoon without a relationship with tidal circulation, except for dissolved oxygen.Key words: Physical-chemical variables, phytoplankton biomass, primary production, subtropical coastal lagoonResumen.-La variabilidad temporal de los datos hidrográficos, nutrientes, clorofila a del fitoplancton y la tasa de producción primaria fueron analizados en la Laguna de Cuyutlán (LC). La temperatura superficial mostró un patrón estacional con valores menores en diciembre y mayores en julio y octubre. La salinidad más baja fue observada en octubre debido a las lluvias estacionales que generaron características estuarinas dentro de la laguna. Las concentraciones de nutrientes ( ) aumentó en febrero y junio como resultado de la remineralización de la materia orgánica, con altas concentraciones de silicato en octubre a causa de las escorrentías de agua dulce a la laguna. Durante los otros meses el silicato disuelto incrementó por la disolución del sílice biogénico. Usando la relación de Redfield como criterio para el balance estequiométrico de nutrientes, se observaron deficiencias de fosfato en LC debido a la asimilación del fitoplancton. La clorofila a aumentó por arriba de 2,0 mg m -3 como consecuencia de agua rica en nutrientes, produciendo una elevada biomasa del fitoplancton. La producción del fitoplancton promedio fue 1,26 g C m -3 d -1 , indicando que la Laguna de Cuyutlán es ∼ 40% más productiva en comparación con otras lagunas costeras subtropicales y templadas. La concentración de clorofila a fue utilizada como criterio para definir el nivel trófico de la LC la cual puede ser descrita como un ecosistema eutrófico. Las variables físicas, nutrientes inorgánicos disueltos y clorofila a...

Pseudo-nitzschia is a cosmopolitan genus, some species of which can produce domoic acid (DA), a neurotoxin responsible for the Amnesic Shellfish Poisoning (ASP). In this study, we identified P. subpacifica for the first time in Todos Santos Bay and Manzanillo Bay, in the Mexican Pacific using SEM and molecular methods. Isolates from Todos Santos Bay were cultivated under conditions of phosphate sufficiency and deficiency at 16˚C and 22˚C to evaluate the production of DA. This toxin was detected in the particulate (DAp) and dissolved (DAd) fractions of the cultures during the exponential and stationary phases of growth of the cultures. The highest DA concentration was detected during the exponential phase grown in cells maintained in P-deficient medium at 16˚C (1.14 ± 0.08 ng mL-1 DAd and 4.71 ± 1.11 × 10 −5 ng cell-1 of DAp). In P-sufficient cultures DA was higher in cells maintained at 16˚C (0.25 ± 0.05 ng mL-1 DAd and 9.41 ± 1.23 × 10 −7 ng cell-1 of DAp) than in cells cultured at 22˚C. Therefore, we confirm that P. subpacifica can produce DA, especially under P-limited conditions that could be associated with extraordinary oceanographic events such as the 2013-2016 "Blob" in the northeastern Pacific Ocean. This event altered local oceanographic conditions and possibly generated the presence of potential harmful species in areas with economic importance on the Mexican Pacific coast.

of the California Current) program conducted measurements of chlorophyll a and phytoplankton production off Baja California. Here, we summarize the main results obtained during the survey period. Long-term means indicated that high productivity occurred along the coastal zone where upwelling occurs, and in a semi-permanent cyclonic gyre off Punta Eugenia. At the seasonal scale, the variability of integrated primary production showed differences with respect to integrated chlorophyll a variability. Integrated chlorophyll a exhibited maximum values during the coastal upwelling season in spring and summer, while minimum values occurred during the inflow of tropical-subtropical waters south of Punta Eugenia in autumn and winter. In contrast, the highest values of integrated primary production occurred in spring and summer to the north of Punta Eugenia, whereas to the south of this location, the highest values occurred in winter and autumn. This seasonal variability was associated with phytoplankton size and maximum photosynthetic rates. At the interannual scale, low productivity was associated with increased stratification during the subarctic water intrusion events and the "Blob" and El Niño events in 2015-2016. Productivity time-series were in agreement with the seasonal variability of the north Pacific Gyre Oscillation index. Given that phytoplankton is the first level of the marine food web, this study contributes to the understanding of regional variations in higher trophic levels at the seasonal and interannual scales.