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Habitat characterization provides predictive information about the distribution of species and is useful for as­sessing habitat quality and population stability. Larval abundance of six frequent and abundant demersal species and the relationship of each with the environment were analysed through generalized additive models to determine their preferential distribution and predictive response to the environmental variables in the southern part of the California Current (25-31°N) between two periods of data collection: 1997-2000 and 2006-2010. Essentially, the main associated variables governing the distribution patterns were related to common and oceanographic characteristics of the water column (temperature and salinity at 50 m depth, dynamic height and degree of water column stratification); however, the set of variables and their ranges are usually species-specific. Species of northern distribution, Sebastes sp. and Citharichtys stigmaeus, were recorded mainly in newly emerged, relatively unstratified waters characterized by a shallow mixed layer and low temperatures. Low dynamic height values were the most significant predictor of larval distribution for Merluccius productus. Citharichthys xanthostigma and Symphurus atricaudus were widespread, distributed across the study area mainly in autumn in unstratified or stratified waters and at a shallow mixed layer. Particularly C. Xanthostigma and S. Lucioceps were related to high dynamic height val­ues, likely influenced by a coastal flow towards the pole, as evidenced by counter-currents. La caracterización del hábitat proporciona información predictiva sobre la distribución de las especies y es útil para evaluar la calidad del hábitat y estabilidad de la población. La abundancia larval de seis especies demersales frecuentes y abundantes y de su relación con el medio ambiente se analizaron a través de modelos aditivos generalizados (GAM) para determinar su distribución preferencial y respuesta a las variables ambientales en la parte sur de la corriente de California (25-31°N) entre dos periodos de datos recolectados 1997-2000 y 2006-2010. Esencialmente, las principales variables aso­ciadas que rigen los patrones de distribución fueron en términos de las variables comunes y oceanográficas de la columna de agua (temperatura y salinidad a 50 m de profundidad, altura dinámica y grado de estratificación de la columna de agua), sin embargo, el conjunto de variables y los rangos suelen ser específicos de la especie. Especies con distribución norteña, Sebas­tes sp. y Citharichtys stigmaeus, se registraron principalmente en aguas de surgencia, identificadas por aguas relativamente no estratificadas, poca profundidad de capa mixta y menor temperatura; y menor altura dinámica, como el predictor más significativo de la distribución de larvas de Merluccius productus. Citharichthys xanthostigma y Symphurus atricaudus se distribuyeron ampliamente a lo largo del área de estudio preferentemente en otoño, en aguas no estratificadas o estratificadas y baja profundidad de la capa de mezcla, pero particularmente C. Xanthostigma y S. Lucioceps en valores altos de alturas dinámicas probablemente influenciadas por el flujo costero hacia el polo indicado por las contracorrientes.

Ocean color is determined by the different components of seawater. Satellite ocean color data are commonly used to infer the inherent optical properties (IOPs) of seawater and concentration of chlorophyll $a$ (Chl- $a$ ). Many of the algorithms that relate satellite data to the components of seawater use global data to determine their parameters. Regionalizing the algorithms is recommended to improve the retrieval of IOPs from satellite data. In this article, we use the in situ and satellite data from the southern part of the California Current System (CCS) off the Baja California Peninsula during 1999 to test the Garver and Siegel IOPs’ inversion model (GSM). The strong seasonal variability observed in the data was not reproduced by this algorithm. Thus, we propose a new regional algorithm whose order and coefficient depend on seasonal variability. This algorithm includes the linear form of the GSM model but allows changes in two parameters according to the season. These two parameters are the magnitude and spectral shape of the relationship of the remote sensing reflectance with the ratio of the backscattering coefficient and the sum of backscattering and absorption coefficients. In this area, both parameters increase gradually from January to October. The new algorithm improves the retrieval of the IOPs’ ratio from an ${r}^{2}$ below 0.5 with the GSM model to an ${r}^{2}$ that ranges from 0.87 in April and October to 0.93 and 0.94 in January and August, respectively. Furthermore, Chl- $a$ data were used as a proxy to evaluate the new algorithm. Absorption data retrieved from remotely sensed data for 1999, 2008, and 2011 relate well to the in situ Chl- $a$ data.

Anomalies occurring in the California Current System during 2013–2016 were examined using remote sensing data and in-situ measurements. Positive anomalies in sea surface temperature (SST, up to 4 °C) and absolute dynamic topography (ADT, up to 20 cm), as well as negative anomalies in satellite chlorophyll concentration (CHL, up to -3.0 mg m -3 ) were recorded. In-situ temperature anomalies in August 2014 increased equatorward, from 2°C along the northernmost line (CalCOFI hydrographic line 76.7) to 10 °C (below ~80 m depth) at the southernmost hydrographic line (off Baja California). In-situ negative Chlorophyll- a (Chl- a ) surface anomalies were similar in most of the lines examined (~ -1.5 mg m -3 ), but for the CalCOFI lines, larger anomalies (~ -3.5 mg m -3 ) were recorded. As a result of increased stratification, mirrored in the increase in mean monthly ADT and the upper water-column temperature, the 2003–2016 CHL time series showed a declining trend in phytoplankton production and biomass, which was particularly pronounced during the last four years in the central and southern zones of the California Current System. The mechanisms responsible for this trend seem to be related to a climate shift from cold to warm in the northeastern Pacific Ocean, as evidenced by large correlations between the CHL anomalies and the Pacific Decadal Oscillation, Multivariate ENSO Index, and Oceanic El Nino indices. Generalized additive models were used to explore the relationship between stratification and the decline in phytoplankton production. Two ADT ranges—characteristic of either highly dynamic or stratified environments—were defined, both of which led to a drop in primary production. The effects of these environments have been associated with the photo acclimation of phytoplankton to irradiance and nutrient availability regimes, by which primary production and biomass decrease due to the limitation of either of these factors. This study reveals some of the effects of the warm anomalies occurring from 2013 to 2016 in the California Current ecosystem, which will help to understand changes in higher trophic levels in this region.

Coastal pollution levels in Todos Santos Bay (TSB) recreational beaches have increased in recent years due to the uncontrolled disposal of wastewater and pollutants to the coast by human activities (urbanization and tourism). In this work, the concentration of water quality parameters along the coast of TSB was evaluated from February 2012 to January 2013. Sampling was carried out at monthly intervals on 29 beach locations. Results showed that the maximum values of all parameters were always found close to the treated wastewater discharge area at Arroyo El Gallo station. Temporally, both nutrients and biochemical oxygen demand reached notably high levels in winter-spring and close to wastewater discharges. During summer, maximum counts of total coliforms and parasite eggs were detected close to wastewater discharges. Overall, our study provides a diagnostic approach on the spatiotemporal variability of water quality parameters for future studies along the coastal waters of TSB.

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 Nino 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. El oceano frente a las costas de la peninsula de Baja California ha sido afectado por diferentes procesos interanuales. Algunos de estos procesos han generado cambios en la circulacion oceanica y en la atmosfera que se han reflejado en la estratificacion de la columna de agua. La estratificacion, definida como la cantidad de energia necesaria para mezclar una columna de agua, determina la disponibilidad de nutrientes necesarios para el crecimiento del fitoplancton. El objetivo de este articulo es describir y relacionar las variaciones interanuales de la biomasa y produccion del fitoplancton con la estructura de la columna de agua. Para esto, se analizaron las series de tiempo (1997–2016) de clorofila a y produccion primaria integradas, profundidad de la picnoclina y de la capa de mezcla y los indices de estratificacion entre la superficie y los 100 y 200 m en la Linea 100 del programa Investigaciones Mexicanas de la Corriente de California (IMECOCAL). Los resultados mostraron que los periodos de mayor estratificacion en la columna de agua fueron durante la intrusion de agua subartica 2002–2007 y El Nino 2015–2016, los cuales trajeron como consecuencia el mayor declive en la biomasa del fitoplancton (en ambos periodos) y de produccion primaria (durante El Nino 2015–2016) en la zona norte frente a Baja California. Finalmente, se relacionaron la tasa fotosintetica maxima y el coeficiente de utilizacion maxima de la luz, con el indice de estratificacion por medio de modelos aditivos generalizados. Estas relaciones explicaron las variaciones interanuales en la produccion primaria en correspondencia con la estratificacion de la columna de agua. Las series de tiempo y el analisis presentado aqui para la linea 100 del IMECOCAL podran ser extrapoladas a otras zonas frente a la peninsula para entender la relacion entre los procesos fisicos con la biomasa y produccion primaria del fitoplancton. Palabras clave: fitoplancton, estratificacion, produccion primaria, Baja California, MECOCAL.

Threshold is defined as the point where small changes in an environmental driver produce large responses in the ecosystem. Generalized additive models (GAMs) were used to estimate the thresholds and contribution of key dynamic physical variables in terms of phytoplankton production and variations in biomass in the tropical-subtropical Pacific Ocean off Mexico. The statistical approach used here showed that thresholds were shallower for primary production than for phytoplankton biomass (pycnocline 0 cm d-1 vs. ADT 4 cm d-1). The relatively high productivity on seasonal (spring) and interannual (La Nina 2008) scales were linked to low ADT (45-60 cm), and shallow pycnocline depth (9-68 m), and mixed layer (8-40 m). Statistical estimations from satellite data indicated that the contribution of ocean circulation to phytoplankton variability was 18% (for phytoplankton biomass), and 46% (for phytoplankton production). Although the statistical contribution of models constructed with in-situ integrated chlorophyll-a and primary production data was lower than the one obtained with satellite data (11%), the fits were better for the former, based on the residual distribution. The results reported here suggest that estimated thresholds may reliably explain the spatial-temporal variations of phytoplankton in the tropical-subtropical Pacific Ocean off the coast of Mexico.

The southern region of the California Current (CC) off Baja California represents a transitional environment, with the influence of low temperature and less saline CC water during spring and summer, and warm and salty tropical and subtropical conditions through the end of summer and autumn. From 2002 to 2006, an anomalous subarctic water (SAW) intrusion generated changes in the epipelagic ecosystem dynamics, affecting phytoplankton biomass and primary production. The goal of the present work is to show the effects of the SAW intrusion off Baja California in the phytoplankton production during the two contrasting years 2002 and 2005. Our results show that the minimum water salinity was associated with density levels of 24.6–25.5 kg m −3 in 2002 and 24.3–25.2 kg m −3 in 2005, indicating that the anomalous SAW intrusion was more pronounced in 2005. In 2005, the mean chlorophyll concentration was low ( −3 ) and associated with negative salinity anomalies ( −3 in 2002 and 2005, although in the coastal zone they were >1.0 mg m −3 in some months. CHL values were significantly different between the north and south zone and among months ( p B ) and maximum photosynthesis rate (P B m )) were one order of magnitude higher in 2005 compared to 2002 ( p −2 d −1 respectively), but similar in 2005 (750 and 1006 mgC m −2 d −1 respectively). The differences between models may be due to the diverse chlorophyll data used in the singular models ( in situ vs. satellite-derived), and to the weight of the phytoplankton photosynthetic parameters in each algorithm. We conclude that for the present data set the Herman and Platt model is more suitable. To assess the relative importance of physical variables, as well as bio-optical and physiological parameters in primary production, we conducted a principal component analysis (PCA). There was an apparent separation between the two years, while each year experienced a special structuring due to different physical variables (mainly salinity, but also temperature and K PAR in 2002, and temperature and water stability in 2005). No clear structuring is discernible in 2005, suggesting that the anomalous SAW intrusion homogenized the pelagic ecosystem. The decrease in primary production suggests a change in phytoplankton biomass as a result of a phytoplankton physiological acclimatization.

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 (PBopt) and Chla concentration. In situ PP estimations using the 14C 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 PBopt 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 PBopt 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 Nino/La Nina. Under both cool-warm hydrographic conditions, the phytoplanktonic community showed large PBopt 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. Se analizo la respuesta de los productores primarios a la variabilidad estacional e interanual de las condiciones hidrograficas en la region sur del Sistema de la Corriente de California (SCC) entre 1997 y 2012. El analisis se basa en la tasa optima de productividad primaria (PP) normalizada por unidad de clorofila (Chla) en la columna de agua (PBopt) y en la concentracion de Chla. Como parte del monitoreo que realiza el programa de Investigaciones Mexicanas de la Corriente de California, se obtuvieron para cada estacion del ano datos de PP in situ con la tecnica de 14C. La informacion se complemento con datos de la temperatura superficial del mar (TSM) medida por el sensor AVHRR de 1985 a 2009. El analisis de los datos de TSM demostro que, en el promedio de largo periodo, la isoterma de 19 oC se ubico en las inmediaciones de punta Eugenia y que su variabilidad espacial permite seguir la alternancia del cambio entre las condiciones frias y calidas. En la escala estacional, esta isoterma presento un marcado desplazamiento latitudinal (de 24oN a 32oN), y se extiendio aun mas durante eventos interanuales asociados a El Nino/La Nina. El valor promedio del PBopt fue de 5.1 ± 3.3 mg C·(mg Chla)–1·h–1 y vario de 0.5 a 17.5 mg C· (mg Chla)–1·h–1. La relacion entre el PBopt y la TSM sugiere un cambio en la comunidad del fitoplancton a los 19 oC, lo que se considero como una respuesta al caracter transicional del SCC. La comunidad fitoplanctonica mantuvo altas tasas promedio de PBopt (~6 mg C·(mg Chla)–1·h–1) en ambas condiciones hidrograficas (frio/calido). Las variaciones en la escala estacional e interanual del PBopt estuvieron asociados a cambios en la composicion y abundancia del nano-microfitoplancton. Los datos sugieren que las altas tasas PP en periodos calidos pueden atribuirse a la contribucion del picoplancton.

Fetch-limited wave grow th was analyzed using high spatial and temporal resolution measurements obt ained with high-frequency (HF) radars. To calculate the wave spectrum, the second-order echo ( S 2 N ) was extracted from the Doppler spectrum and mapped to the wave frequency domain. The conversion of S 2 N to the wave frequency spectrum was carried out us ing a linear parametric model dependent on wind speed. Wave growth, represented by the dime nsionless energy and peak frequency as a f unction of dimensionles s fetch, was determ ined from the spectra calculated for 25 cells (~400 km 2 ) in the vicinity of a moored AirSea Interacti on Spar buoy. The buoy data were used as reference and to provide the wind informa tion required for the wave growth analysis. The simultaneous data from the buoy and HF radars sh owed a suitable agreement with the wave growth curves. The analysis of the 25 cells showed an adequate agreement and certain dispersio n around the growth curves. Possible causes of this disp ersion are related to errors in the est imation of the frequency spectrum and fetch, and the assumption of homogeneous wind conditions. Fr om the limited data set used, it was not possible to prove any impact of swell on wave growth ; however, it is possible that analysis over a wider range of swell heights may provide this evidence. Neverthe less, the results suggest that the linear parametric model is able to re produce fetch-limited wave growth. This work represents th e first effort focu sed on fetch-limited wave growth using HF radars.

We conducted a study from January 2002 to February 2008 on silicoflagellate fluxes in Alfonso Basin at the entrance to the Gulf of California. Thirteen taxa were identified in sediment trap samples, with Octactis pulchra as the dominant species. Total flux climatology reached a maximum value of 5×106 skeletons m-2 day-1 in December and then sharply decreased to a minimum value in February (2.3×103 skeletons m-2 day-1) concurrently with the climatological sea surface temperature (SST) minimum. Subsequently, there was a positive trend with a second relative maximum of 1.6×106 skeletons m-2 day-1 in September coincident with a maximum in climatological SST. During this period, there was a similar increase to 1.4×106 skeletons m-2 day-1 in May. Factor analysis identified three patterns of variation: “subtropical oceanic,” “subarctic,” and “equatorial El Niño.” Factors had reasonable correlations with the Pacific decadal oscillation (PDO), North Pacific Gyre oscillation (NPGO), and El Niño Modoki indices (r=0.53, 0.67, and 0.63, respectively). The first and second modes were apparently linked to decadal climatic conditions correlated to PDO and NPGO, as suggested by the silicoflagellate species Dictyocha messanensis forma messanensis and the assemblage of D. epiodon and Distephanus speculum, respectively; the third mode was related to the presence of warm equatorial-oceanic waters identified by D. messanensis forma spinosa, which defines El Niño influence. These results demonstrate the importance of the region where there is a confluence of the low-frequency, high-latitude PDO, NPGO, and high-frequency El Niño signals.

The temporal variability of the physical and chemical conditions of coastal waters off Ensenada, Baja California (Mexico) was characterized. A historical analysis was made based on 11 years (1998–2008) of temperature and salinity data records measured quarterly by IMECOCAL, along a transect perpendicular to the coast (CalCOFI line 100). Moreover, the physical and chemical conditions at a coastal monitoring observatory called station ENSENADA were described using a 2-year data series (October 2006–November 2008) obtained with improved temporal resolution. The historical analysis of line 100 showed marked seasonal variability in the thermohaline conditions associated with fluctuations in the flow of the equatorward California Current and the poleward California Undercurrent, as well as with coastal upwelling events whose magnitude and frequency increase towards spring–summer. Interannual variability was also observed, related to warm and/or cold ENSO phases that modify the characteristics of the water column in this coastal region. The most striking characteristics of the interannual variability at station ENSENADA were La Nina conditions recorded from summer 2007 to mid 2008. During this cold ENSO phase, temperature, salinity, dissolved oxygen, density, and dissolved inorganic carbon data revealed the anomalous presence of subsurface water at the surface layers in spring 2008. Results suggest that the coastal observatory is sensitive to the temporal variability of hydrographic conditions on shelf coastal waters (

Oceanographic conditions in the Pacific waters off Baja California are described for the period 2002–2003. Anomalies in the temperature-salinity relationships were observed from October 2002 to April 2003, with a clear contribution of low salinity and low temperature subarctic water in the upper 100 m of the water column. Below 100 m, physical data suggested weak El Niño conditions. Weakened or poleward winds were not observed. The pelagic ecosystem during the intrusion of subarctic waters showed strong seasonal changes, with localized centers of high chlorophyll and zooplankton in July 2002, followed by a strong decrease in the following autumn and winter seasons. Both chlorophyll and zooplankton rebounded in April 2003, but zooplankton showed a stronger onshore-offshore gradient. There was no strong biological signal. The zooplankton taxa that showed an increase during El Niño 2002–2003 were salps and chaetognaths. The increase of salps did not appear to be related to this event, due to their seasonal occurrence limited to the northern region. In contrast the increase of chaetognaths presented a similar pattern to that observed in El Niño 1997–1998.

Sea surface current measurements and wind stress and sea surface temperature satellite data were used to study the effect of northerly wind events (Tehuanos) on coastal dynamics in the Gulf of Tehuantepec, Mexico. The winter 2005 observations show a significant change in the intensity and direction of surface currents during wind events, which is reflected in an increase in kinetic energy and negative relative vorticity. The analysis revealed that kinetic energy of the coastal current decreases (increases) in periods when there is absence (presence) of Tehuano wind events, and that the relative vorticity has a tendency to positive values under low wind conditions and a tendency to negative values during high wind events. An asymmetric ocean response was observed due to wind stress forcing and the interaction between a persistent coastal current and offshore wind stress. Con base en mediciones de corrientes superficiales del océano e información satelital de vientos y temperatura superficial del océano, se estudió el efecto de los eventos de viento del norte (tehuanos) sobre la dinámica costera en el golfo de Tehuantepec, México. Las observaciones realizadas durante el invierno de 2005 mostraron un cambio significativo en la intensidad y dirección de las corrientes superficiales durante los eventos de viento, que se vio reflejado en un aumento de la energía cinética y de la vorticidad relativa negativa. El análisis mostró que la energía cinética de la corriente costera decrece (incrementa) en los periodos cuando hay ausencia (presencia) de eventos de viento tehuano, y que la vorticidad relativa presenta una tendencia a valores positivos bajo condiciones de viento débil y una notoria tendencia a valores negativos durante los eventos de viento intenso. Se observó una asimetría en la respuesta del océano por el forzamiento del esfuerzo del viento y la interacción entre una corriente costera persistente y el viento normal a la costa.

The freshwater discharge of the Colorado River into the Gulf of California has been reduced to negligible quantities since the construction of the Hoover Dam in 1935. These radical anthropogenic changes in the hydrography of the Colorado River Delta had striking repercussions on both physical and biological processes. Using historical river discharge data, the changes in the flow dynamics and hydrographic patterns before and after the drastic freshwater reduction are studied numerically, using a three-dimensional nonlinear shelf model. The results are applied to assess the environmental impact of the reduction of river discharge on the area. Satellite imagery is also used to compare our results with observed fronts.

BACKGROUND: Highly productive hotspots in the ocean often occur where complex physical forcing mechanisms lead to aggregation of primary and secondary producers. Understanding how hotspots persist, however, requires combining knowledge of the spatio-temporal linkages between geomorphology, physical forcing, and biological responses with the physiological requirements and movement of top predators. METHODOLOGY/PRINCIPAL FINDINGS: Here we integrate remotely sensed oceanography, ship surveys, and satellite telemetry to show how local geomorphology interacts with physical forcing to create a region with locally enhanced upwelling and an adjacent upwelling shadow that promotes retentive circulation, enhanced year-round primary production, and prey aggregation. These conditions provide an area within the upwelling shadow where physiologically optimal water temperatures can be found adjacent to a region of enhanced prey availability, resulting in a foraging hotspot for loggerhead sea turtles (Caretta caretta) off the Baja California peninsula, Mexico. SIGNIFICANCE/CONCLUSIONS: We have identified the set of conditions that lead to a persistent top predator hotspot, which increases our understanding of how highly migratory species exploit productive regions of the ocean. These results will aid in the development of spatially and environmentally explicit management strategies for marine species of conservation concern.