Abstract. The population structure of Centropages furcatus associated with hydrographic structures in late spring 2004 was analyzed. The distribution of the different copepodite stages of C. furcatus was analyzed from zooplankton samples obtained with a bongo net. The hydrography and geostrophic velocity in Bay of La Paz relative to the bottom depth revealed the presence of a cyclonic gyre in the Alfonso basin area and a thermohaline front near Boca Grande. The distribution of vertically integrated chlorophyll a concentration showed maximum values at the center of the gyre and in the region of the front, making evident that both hydrographic structures stimulated biological productivity because of the flux of nutrients into the euphotic layer in the gyre and the nutrient accumulation in the thermohaline front. The results showed that the spatial variation of C. furcatus was influenced by both hydrographic structures. The differential distribution of the copepodite stages was noticeable in the cyclonic gyre, with the highest density for the first copepodite stages at the center of the gyre because of the high chlorophyll a concentration due to the nutrient enrichment in the euphotic layer, as a result of Ekman pumping. Copepod density was higher in the thermohaline front than inside the cyclonic gyre because the front serves as a reproductive spot for the species, maintaining a stable adult population density inside the bay and in the Gulf of California.

Resumen. Se analizó la estructura poblacional de Centropages furcatus asociada a estructuras hidrográficas a finales de la primavera de 2004. La distribución de los diferentes estadios de copepoditos de C. furcatus fue analizada a partir de las muestras de zooplancton obtenidas con una red bongo. En la bahía de La Paz, la hidrografía y la velocidad geostrófica relativa al fondo revelaron la presencia de un giro ciclónico en la cuenca Alfonso y un frente termohalino cerca de Boca Grande. La distribución de la concentración de clorofila a integrada verticalmente mostró valores máximos en el centro del giro y en la región del frente, lo que evidenció que ambas estructuras hidrográficas favorecen la productividad biológica debido al flujo de nutrientes hacia la capa eufótica en el giro y a la acumulación de nutrientes en el frente termohalino. Los resultados mostraron que la variación espacial de C. furcatus estuvo influenciada por ambas estructuras hidrográficas. En el giro ciclónico se observó una distribución diferencial por etapa de desarrollo, con mayor densidad poblacional de los primeros estadios de copepoditos en el centro del giro, como consecuencia de la alta concentración de clorofila a por el enriquecimiento de nutrientes en la capa eufótica, debido al bombeo de Ekman. La densidad poblacional de copépodos fue mayor en el frente termohalino que en el interior del giro ciclónico, debido a que el frente actúa como una zona reproductiva de la especie que mantiene una densidad poblacional estable para los adultos de la bahía y del golfo de California.

ABSTRACT Biomass is a valuable indicator of biological production in any ecosystem and represents a proxy of secondary production in the case of zooplankton. This short communication aims to report zooplankton biomass values in the waters of the Campeche Canyon, southern Gulf of Mexico, during the “Nortes” storm season of 2011 and to explore their relationship with the hydrography and the circulation pattern. The results showed the presence of cyclonic and anticyclonic eddies associated with high and low water density at the base of the pycnocline. The highest values of zooplankton biomass (>40 g 100 m-3) were observed in regions that presented higher water density values (~26.1 kg m-3). In comparison, the lowest zooplankton biomass values (<5 g 100 m-3) were associated with low water densities (<25.6 kg m-3). The results presented here contribute to elucidating the role that physical forcing plays on the zooplankton biomass of the region, particularly during a season in which the passage of extreme storms is widespread.

Resumen. Los copépodos, como uno de los principales grupos que componen el zooplancton marino, juegan un papel importante por su posición en la red trófica. Se evaluó la biomasa de copépodos en un vórtice ciclónico durante 2 estaciones climáticas contrastantes en la bahía de La Paz, al sur del golfo de California, la cual se caracteriza por una alta productividad biológica. Durante 2 campañas oceanográficas en invierno de 2006 y verano de 2009, se determinó la estructura física de la columna de agua mediante un CTD y se recolectaron muestras de zooplancton mediante arrastres oblicuos. Se utilizaron datos de satélite para visualizar los patrones de distribución de clorofila a (Cla). Los resultados mostraron un vórtice ciclónico en ambas estaciones, con un diámetro de ~25 km y velocidades geostróficas >50 cm·s-1 en su periferia, con elevada Cla (~3 mg·m-3 en invierno). La máxima biomasa de calanoides ocurrió en invierno, con hasta 6.6 mg·100 m-3 en el oeste de la bahía, cerca de la costa; además, su distribución coincidió con el patrón de Cla y circulación, ya que formó un anillo siguiendo la periferia del vórtice, con un segundo pico cerca de la conexión con el golfo. Los valores medios de biomasa de copépodos mostraron un patrón de alternancia calanoides-ciclopoides entre invierno y verano dentro del vórtice ciclónico, con más biomasa de calanoides que ciclopoides en invierno y lo contrario en verano. Los resultados resaltan el impacto del vórtice en el ecosistema planctónico a través de su influencia sobre las condiciones hidrográficas en la columna de agua. Otros factores, como las interacciones ecológicas, la dinámica poblacional y los hábitos alimenticios, también pueden jugar un papel importante. El comportamiento alimentario es afectado por altas concentraciones de Cla, que representan una fuente de alimento para copépodos observados alrededor del vórtice.

Abstract. As one of the main groups comprising marine zooplankton, copepods play an important role due to their position in the trophic web. We assessed the copepod biomass in a cyclonic eddy during 2 contrasting seasons in the Bay of La Paz, southern Gulf of California, which is characterized by high biological productivity. Two oceanographic expeditions took place in the winter of 2006 and the summer of 2009; a CTD probe was used to determine the physical structure of the water column, and oblique zooplankton hauls collected zooplankton samples. Satellite data were used to visualize the chlorophyll a (Chla) distribution patterns. The results showed a well-defined cyclonic eddy in both seasons, with a diameter of ~25 km and geostrophic velocities >50 cm·s-1 in its periphery. At the edges of the eddy, Chla was high, reaching ~3 mg·m-3 in winter. The maximum calanoid copepod biomass occurred in winter, reaching 6.6 mg·100 m-3 in the western bay close to the coast; moreover, their distribution corresponded well with the Chla and circulation patterns, forming a belt shape following the periphery of the eddy, with a second peak close to the connection with the gulf. The mean values of copepod biomass exhibited a pattern with alternating calanoids-cyclopoids between winter and summer within the cyclonic eddy, with calanoid biomass higher than cyclopoid biomass in winter, which was the opposite of summer. The results highlight the impacts of the eddy on the planktonic ecosystem through its influence on the hydrographic conditions in the water column. Other factors, such as ecological interactions, population dynamics, and feeding habits, may also play a role. Feeding behavior is affected by the high concentrations of Chla, which represent a source of food for copepods observed around the eddy.

ABSTRACT In 2014, an unexpected and unusual warm patch of ocean water was discovered in the northeast Pacific Ocean (PO) that moved south, reaching the Mexican coasts; this patch, returning in 2019, was nicknamed “the Blob”. This paper aimed to assess the impacts of this phenomenon on the sea surface temperature (SST) and chlorophyll-a (CHLA) levels in the Gulf of California (GC), a high-productivity region. Daily satellite images of SST and CHLA with a spatial resolution of 1 km/pixel were obtained for 2014, 2017, and 2019 from the Moderate Resolution Imaging Spectroradiometer (MODIS). Two disc-shaped areas of around 25 km in diameter were selected in the southern portion of the GC to assess the variability of both parameters quantitatively. An additional site was selected in the PO for comparison and, thus, to better characterize and have a complete vision of these events. The results showed that in the PO, during the periods in which the Blob occurred, the SST values were higher concerning the neutral year (2017), and the levels of CHLA were very low (barely 0.15 mg m−3). Within the GC, the results showed the presence of a strong seasonal variability, with maximum values of SST (>30°C) and the lowest concentrations of CHLA (<2 mg m−3) during the summer, with maximum concentrations of CHLA (∼10 mg m−3) observed during the winter months. Contrary to expectations, no dramatic changes in SST and CHLA were observed during the years impacted by the Blob. This apparent absence of negative impacts could be related to different mechanisms in the gulf that “protect” to avoid climate disruptions. The presence of complex geomorphology and hydrodynamic processes at different scales induce mixing and fertilizing of the euphotic layer. Could these factors protect the southern gulf from the negative impacts of the Blob?

ABSTRACT Phytoplankton is a sentinel group of organisms of climate change due to their capacity to respond to multiple stressors, so studies documenting the optimal optical conditions within the water column affecting their growth and production are imperative. As a contribution to this topic, this study report selected optical properties in deep-waters of the Gulf of Mexico by in situ measurements during summertime. A multidisciplinary research cruise was carried during August/September of 2018. A CTD instrument configured with underwater quantum and fluorescence sensors were used to acquire data of temperature, conductivity, depth, photosynthetically active radiation (PAR), and fluorescence of chlorophyll-a, which were used to determine selected optical coefficients, including the light extinction (k), the compensation light intensity (Ec), the compensation depth (Zc), the critical depth (Zcr), and the incident irradiance (E0). The Brunt-Väisälä frequency calculated from CTD data was used as a magnitude indicator of the water column stratification. The results showed a pycnocline located between 23 and 68 m depth, and favorable conditions for phytoplankton production with high values of E0 reaching 1523.4 μmol m−2 s−1, Ec values ranging from 3 to 8 μmol m−2 s−1, values of Zcr greater than Zc and maximum records of k values of 0.06. Based on multivariate statistical techniques, two zones were clearly defined. These results represent the first observational report on the optical properties in the deep region of the Gulf of Mexico. Studies on the ideal optical conditions for carrying out phytoplankton photosynthesis and their possible seasonal and interannual variability are essential to understand the processes that support the phytoplankton production, especially in regions that are characterized by their high biodiversity.

ABSTRACT Marine zooplankton play key roles in the transfer of energy to higher trophic levels and the removal of CO2 from the atmosphere through the sedimentation of inorganic and organic carbon compounds included in their fecal pellets. Therefore, differences in the zooplankton groups driven by climate variations could influence the biogeochemical cycles at large oceanic scales. As a contribution to this topic, we analyzed the zooplankton groups in the Bay of La Paz, Gulf of California, Mexico, a highly dynamic basin characterized by its high biological productivity. We used information gathered during multidisciplinary research cruises in the summers of 2008 and 2009. The results showed differences in the hydrographic parameters between both summers, with a higher temperature recorded in 2009. The zooplankton groups showed that the calanoid copepods were the most abundant; however, there were important differences in the relative abundance of the rest of the analyzed groups as an effect of the temperature distribution along the study area, which was confirmed by multivariate statistical methods. These temperature changes were associated with increased gelatinous zooplankton (Cnidaria, Chaetognatha, Appendicularia, and Ctenophora) in 2009 in a region where the temperature was higher, possibly as a result of changes in food (phytoplankton) availability.

Abstract: Information on selected bio-optical properties and primary production values of the waters of the Bay of La Paz, southern Gulf of California, is reported during June 2004, a region characterized to have very rich biodiversity, including endemic and endangered species, with high ecological relevance. In-situ measurements of natural fluorescence and photosynthetically available radiation (PAR) enabled the subsequent calculation of the incident irradiance (E 0 ), the light extinction coefficient (k), compensation depth (Z c ) and critical depth (Z cr ). The results suggest the presence of light propitious conditions for phytoplankton community growth and net primary production, which are highly significant for the potential development of models of light penetration, ocean color, primary productivity, and analyses of organic carbon energy flow.

ABSTRACT The optical properties of the water column have a significant influence on phytoplankton growth. In this work, we report selected optical property values of the waters of two regions in the southern Gulf of Mexico. Measurements of natural fluorescence and photosynthetically available radiation (PAR) were made during a multidisciplinary research cruise, enabling the subsequent calculation of the light extinction coefficient (k), compensation depth (Zc), critical depth (Zcr), and compensation light intensity (Ec). The results revealed an interesting contrast between the two areas but also indicated the presence of optimal conditions for phytoplankton community growth and net primary production. These data, as reported here, could set the stage for the development of bio-optical models of light penetration, ocean color and primary productivity in the region, as well as for future analyses of organic carbon energy flow. However, many more studies are required to establish the possible seasonal variations in these parameters, which could be linked to the wide variability of the region.

The ocean is characterized by a circulation dominated by vortex of different sizes; the vortex play a very important role in the oceanic climate as they transport energy, mass and organisms. Their study is therefore of first importance to understand the different processes that occurring in the seas at different time-space scales. The Bay of Campeche, in the southern Gulf of Mexico, is characterized by a cyclonic circulation. With the aim of identifying the origin and the formation of the cyclonic vortex, data of currents registered in an oceanographic survey and data of sea altimetry obtained with remote sensors were analyzed. From the results, the formation of the cyclonic vortex of the Bay of Campeche depends mainly on the conservation of the potential vorticity.

El océano se caracteriza por una circulación dominada por giros de diferentes tamaños; los giros juegan un papel muy importante en el clima oceánico ya que transportan energía, masa y diversos organismos. Su estudio es por tanto de primera importancia para entender los diferentes procesos que ocurren en los mares a diferentes escalas espacio -temporales. La Bahía de Campeche, en el sur del Golfo de México se caracteriza por tener una circulación de tipo ciclónica. Con la finalidad de identificar el origen y la formación del giro ciclónico se analizaron datos de corrientes registradas en una campaña oceanográfica y datos de altimetría del mar obtenidos con sensores remotos. De los resultados obtenidos se deduce que la formación de los giros ciclónicos de la Bahía de Campeche depende principalmente de la conservación de la vorticidad potencial.

Abstract: There exist previous studies on phytoplankton, its taxonomic groups and species, its biomass and primary productivity, mainly in winter and spring, but the structure of the phytoplankton from the Gulf of Tehuantepec in summer is poorly known. The composition and distribution of the phytoplankton photosynthetic pigments in summer conditions are provided in this paper. Hydrographic data from nine stations, during an oceanographic cruise in June, 20013, and analysis of five major phytoplanktonic pigments, Fucoxanthin, Prasinoxanthin, Violaxanthin, Zeaxanthin (marker of Synechococcus, picoplanktonic prokaryote) and Divinyl-chlorophyll a (diagnostic of Prochlorococcus, another picoplanktonic prokaryote) are given. Column water was well-stratified: surface layers had a thickness between 20 and 35 m, with well-defined thermoclines at those depths. Values of all pigments were low, but they showed similar vertical distribution patterns, with subsurface maxima peaks (between 30 and 40 m), especially Divinyl-chlorophyll a in most stations, except 3 and 4, where Fucoxanthin was the most important pigment. These peaks did not always coincide with the depths of the main thermocline at each station, buy usually they were found below the thermocline. This scenery shows the picoplankton as a very important size-fraction group in summer (at least in June), strongly contrasting with the winter-spring conditions, of intense turbulent mix and upwellings, where microplankton and diatoms appear to predominate.

Resumen: Existen estudios previos sobre fitoplancton y sus grupos taxonómicos y especies, así como de su biomasa y productividad primaria, principalmente en invierno y primavera, pero se conoce poco la estructura del fitoplancton del Golfo de Tehuantepec en verano. Aquí se dan a conocer la composición y distribución de pigmentos fotosintéticos fitoplanctónicos en condiciones de verano. Se obtuvieron datos hidrográficos en nueve estaciones durante un crucero oceanográfico en junio, 2003, y se analizaron cinco pigmentos, Fucoxantina, Prasinoxantina, Violaxantina, Zeaxantina (indicador de Synechococcus, procarionte del picoplancton) y Divinil-clorofila a (diagnóstico de Prochlorococcus, otro procarionte del picoplancton). La columna de agua se encontró estratificada: la capa superficial, definida por la profundidad del tope de la termoclina, varió entre 20 y 35 m de espesor. Los valores de todos los pigmentos fueron bajos, pero mostraron patrones similares de distribución vertical, con un pico de concentración subsuperficial (entre 30 y 40 m), destacando Divinil-clorofila a en la mayoría de las estaciones, excepto en la 3 y 4, donde la Fucoxantina fue el principal pigmento. Estos picos no siempre coincidieron con la profundidad de la termoclina en cada estación, generalmente éstos se encontraron por debajo de ella. Este escenario muestra al picoplancton como una fracción importante en verano (al menos en junio), contrastando notablemente con la condición de invierno-primavera, de intensa mezcla turbulenta y surgencias, donde el microplancton y las diatomeas predominan.

Este estudo analisou o papel das forçantes barotrópica e baroclínicadas marés na agregação e dispersão do ictioplâncton no sul do Golfo do México. A amostragem do ictioplâncton e o cálculo dos parâmetros hidrográficos foram realizados durante Setembro de 1992 num ponto fixo de 180 m de profundidade, perto da quebra de plataforma (19º32'N - 92º38.5'W). Uma amostragem de tipo yoyo com CTD foi realizada durante 24 h e amostras biológicas foram tomadas a cada 2 h. Estas medidas foram combinadas com dados de densidade da água e velocidade obtidas de simulações do modelo do Sistema Regional de Modelo dos Oceanos (ROMS). Uma termoclina e duas haloclinas foram detectadas. O número de Froude aumentou com uma defasagem de 2 h com relação à maré barotrópica, sugerindo a existência de uma maré baroclínica. A agregação e a dispersão do ictioplancton mostraram variações verticais tanto em abundância quanto no número de taxa e larvas, com defasagem de 5 h em relação à máxima maré barotrópica e esteve em fase com a oscilação da termoclina. A oscilação vertical foi atribuída a um controle hidráulico forçado pela maré interna.

The role of vertical barotropic and baroclinic tidal forcing in the aggregation and dispersion of ichthyoplankton in the Southern Gulf of Mexico was analyzed in this study. Samplings of ichthyoplankton and the determination of hydrographic parameters were performed during September 1992 at a single point of 180 m depth, near the shelf break (19º32'N - 92º38.5'W). A 24 h CTD yo-yoing casting and biological samples were taken every 2 h and these measurements were combined with water velocity and density simulations from the Regional Ocean Model System (ROMS). One thermocline and two haloclines were depicted. The Froude number increased with a 2 h lag with respect to the maximal barotropic tide, suggesting the existence of a baroclinic tide. Aggregation and dispersion of the ichthyoplankton showed vertical oscillations in the abundance and the numbers of taxa and larvae with a 5 h lag with respect to the maximal barotropic tide and were in phase with the thermocline oscillation. The vertical oscillation was attributed to a hydraulic control forced by the internal tide.

Abundância e distribuição do picofitoplâncton autotrófico total (PFP), temperatura, salinidade, PAR e clorofila-a, foram determinados em dois ambientes presumivelmente diferentes: (1) duas áreas costeiras (perto da foz de três rios) e (2) uma área oceânica (Campeche Canyon), ambas situadas ao sul do Golfo do México, durante a "estação seca" (Junho-Julho, 2004). Os picoprocariontes Prochlorococcus e Synechococcus foram identificados por TEM, e as populações de Synechococcus e de picoeucariontes também foram reconhecidas por citometria de fluxo. A maior abundância de PFP (1,67 × 105 células ml-1) foi encontrada em águas rasas (~ 10 m de profundidade) em torno dos rios Grijalva Usumacinta, seguida de uma estação perto do Rio Coatzacoalcos (1,19 × 105 células ml-1). As abundâncias de PFP em Campeche Canyon foram geralmente menores (máximo 1,53 × 104 células ml-1). A maior variabilidade em abundâncias de PFP foi encontrada em estações costeiras quando comparado às águas oceânicas, e quase não houve correlação entre os padrões de clorofila-a e abundância de PFP. Picos de PFP foram detectados nas áreas costeiras e oceânicas, mas em Campeche Canyon localizaram-se em maior profundidade (60 m), relativamente mais perto do local onde se registrou o máximo de clorofila (cerca de 75 m). Os resultados sugerem que as populações de PFP englobam um componente fotossintético substancial em ambas as águas costeiras e oceânicas do sul do Golfo do México.

The abundance and distribution of total autotrophic picophytoplankton (PFP), temperature, salinity, PAR, and chlorophyll a were determined in two presumably contrasting environments: (1) two coastal areas (close to the mouths of three rivers), and (2) one oceanic area (Campeche Canyon), of the southern Gulf of Mexico, during the "dry season" (June-July, 2004). The picoprokaryotes Prochlorococcus and Synechococcus were identified by TEM, whereas Synechococcus and picoeukaryotes populations were also recognized by flow cytometry. The highest PFP abundance (1.67×105 cells ml-1) was found in shallow waters (~10 m depth) around the Grijalva-Usumacinta river mouth, followed by that found at a station close to the Coatzacoalcos River (1.19×105 cells ml-1); PFP abundances in the Campeche Canyon were usually lower (maximum 1.53×104 cells ml-1). Greater variability in PFP abundances was found in coastal stations than in oceanic waters, and weak relationships appeared between the patterns of chlorophyll a and PFP abundance. Peaks of PFP were detected in both coastal and more oceanic areas, but in the Campeche Canyon they were located deeper (60 m), relatively closer to the deep maximum of chlorophyll (located at about 75 m). Results suggest that PFP populations include a substantial photosynthetic component in both coastal and oceanic waters of the southern Gulf of Mexico.

Se discute la importancia de los vórtices en el transporte de energía interna (calor), sales, nutrientes y sedimentos en los ecosistemas marinos y continentales. Se presentan los efectos de afloramientos de la termoclina y nutriclina ocasionados por la formación de remolinos ciclónicos, los cuales se resumen en un incremento de nutrientes hacia la zona eufótica, lo que conlleva al aumento en producción biológica. También se discuten los efectos de los remolinos anticiclónicos en el transporte de clorofilas y sedimentos a grandes distancias comparadas con sus diámetros. El corolario principal es la necesidad de un trabajo conjunto de las diferentes disciplinas, para un completo entendimiento de los fenómenos que coadyuve a predecir y obtener una razonable explotación de los recursos marinos.

The importance of vortices as one of the principal actors in transporting the internal energy (heat), salts, nutrients and sediments in marine and continental ecosystems is discussed. The thermocline and pycnocline uplift effects caused by the formation of cyclonic vortices, which bring about an increase in nutrients in the euphotic zone, are presented. Also, the effects of anticyclonic vortices in the transport of chlorophyll and sediments over large distances compared to their diameters, are described. The end result is the need of joining efforts by different disciplines to achieve a complete understanding of the phenomena, which could help to predict and reasonably exploit marine resources.

Neste ensaio fala-se da importância dinâmica dos remoinhos como um dos principais atores na transportação de energia interna (calor), sales, nutrientes e sedimentos nos ecosistemas marinhos e continentais. Apresentam-se tambem alguns de seus efeitos no oceano como as urgências causadas pela formação de remoinhos ciclônicos, que têm como consequência um incremento de nutrientes à zona eufôtica. Por outro lado, fala-se tambem sobre os efeitos dos remoinhos anticiclônicos na transportação de clorofilas e sedimentos à grandes distâncias comparadas com os seus diâmetros. O corolario principal é a necessidade de um trabalho conjunto das diferentes disciplinas, para um completo entendimento dos fenômenos que ajude a predizer e a obter uma razoável explotação dos recursos marinhos.