The Northern Current and its interaction with the Blanes submarine canyon (NW Mediterranean Sea)

A high-resolution (~1.2km) 3D circulation model nested in one-way to a coarse-resolution (~4km) 3D regional model was used to examine the interaction between the Northern Current and the Blanes submarine canyon (~41°00’-41°46’N; ~02°24’-03°24’E); paying particular attention to upwelling/downwelling events and cross-shelf break water exchange. A Lagrangian particle-tracking algorithm coupled to the high-resolution 3D circulation model was also used to examine the role of the Northern Current (NC) and its seasonal variability on the dispersion of passive particles and residence time within Blanes Canyon (BC). Although it refers to a climatological simulation (i.e. no interannual variability), at this resolution, the Rossby radius of deformation for the Mediterranean Sea (5-12 km) is resolved. Therefore the numerical modeling system properly suites our purpose, since it adequately reproduces the NC mesoscale variability and its seasonality. Satisfactory validation of model results with remote sensing and in-situ observations supports the present findings. The simulated NC tends to be fast and deep in winter, and slow and shallow in summer. NC meanders and eddies are recurrent in the BC area and produce highly fluctuating three-dimensional circulation patterns within the canyon. NC meanders and anticyclonic eddies propagating along the current pathway tend to be deep and, consequently, their effects extend down to the deeper part of BC. The meandering of the NC plays a key role in enhancing vertical motions within the canyon. NC meanders produce an oscillation of the vertical flow characterized by net upwelling when the meander is located over the upstream side of the canyon followed by net downwelling as the meander moves downstream. Associated with NC meanders passing over BC, upwelling and downwelling events occur on timescales of 4 to 20 days and they are more frequent in winter. These findings provide further evidence that continuous downwelling favourable (right-bounded) flows can produce net upwelling inside submarine canyons. Concerning cross-shelf break water exchange, one significant finding from this study is that the amount of water moved across the shelf break at the upstream upper canyon wall is approximately two times larger than the amount of water moved downstream. This preferential zone for cross-shelf break exchange is related to the asymmetry of the shelf break geometry that is characterized by a sharp curvature upstream. Results also show that cross-shelf break water exchange is higher (~30%) in winter than in summer. On the other hand, particle-tracking experiments show that passive particles released from the mid-shelf to the upper-slope drift along the shelf edge with a net downward movement within the upper canyon. They also show that particle dispersion is higher in winterthan in summer and that particles travelling below the canyon rim (i.e. below 100 m depth) have longer residence times within the canyon.Un modelo de circulación 3D con resolución de ~1.2km anidado en una vía a un modelo regional 3D con resolución de ~4km, fue empleado para estudiar la interacción entre la Corriente del Norte y el cañón submarino Blanes (~41°00’-41°46’N; ~02°24’-03°24’E). Se hace especial énfasis en los eventos de elevación y hundimiento de agua, así como en el intercambio de agua a través del borde de la plataforma continental. También se uso un algoritmo Lagrangiano alimentado con los campos de velocidad del modelo de alta resolución para estudiar el papel de la Corriente del Norte (NC, por sus siglas en inglés) y su estacionalidad en la dispersión de partículas pasivas y tiempos de residencia dentro del Cañón Blanes (BC, por sus siglas en inglés). Aunque se trata de una simulación climatológica (i.e. sin variabilidad interanual), el radio de deformación de Rossby para el Mar Mediterráneo (5-12km) es resuelto. Por lo tanto, el sistema de modelado es de una resolución apropiada para nuestros objetivos ya que reproduce adecuadamente la NC y su estacionalidad. Los resultados comparan satisfactoriamente con información de imágenes de satélite y observaciones in-situ. Los resultados indican que la NC tiende a ser rápida y profunda en invierno, y lenta y somera en verano. El paso de meandros en la NC y remolinos es un rasgo frecuente en el cañón Blanes. En particular, meandros y remolinos anticiclónicos que se propagan siguiendo la trayectoria de la NC tienden a ser profundos y, consecuentemente, sus efectos se extienden hacia la parte profunda del cañón. Nuestros resultados también indican que los meandros en la NC juegan un papel importante en el aumento del movimiento vertical dentro del cañón. Estos meandros producen una oscilación del flujo vertical caracterizado por una elevación neta de agua conforme el meandro pasa sobre el lado Este del cañón seguido por un hundimiento neto conforme el meandro se mueve hacia el lado Oeste. Eventos de elevación y hundimiento de agua en escalas temporales de 4 a 20 días están asociados al paso de meandros, siendo estos eventos más frecuentes en invierno. Estos resultados aportan más evidencia de que flujos continuos con la costa a la derecha (i.e. favorables para el hundimiento de agua) pueden producir elevación neta de agua dentro de cañones submarinos. Con relación al intercambio de agua a través del borde de la plataforma continental, un resultado importante del presente estudio es que la cantidad de agua que pasa a través del borde de la pared Este del cañón es aproximadamente el doble de la cantidad de agua que pasa a través del borde de la pared Oeste. Esta zona preferencial para el intercambio de agua está relacionada con la curvatura del borde de la plataforma continental, la cual es más pronunciada sobre la pared Este del cañón. Los resultados también indican que el intercambio de agua es mayor (~30%) en invierno que en verano. Por otro lado, partículas pasivas liberadas sobre la plataforma y la pendiente continental derivan a lo largo del borde de la plataforma con un movimiento neto hacia abajo dentro del cañón. Los resultados también muestran que la dispersión de partículas es mayor en invierno que en verano. Finalmente, los resultados indican que el tiempo de residencia tiende a incrementarse con la profundidad, así las partículas que se mueven por debajo de la profundidad del anillo del cañón (i.e. por debajo de 100 m de profundidad) presentan un tiempo de residencia mayor dentro del cañó

Estructura poblacional y biología reproductiva del tiburón martillo Sphyrna lewini (Carcharhiniformes: Sphyrnidae) capturado en la pesca artesanal de Oaxaca, México.

Background: Sphyrna lewini, is a semi-oceanic and cosmopolitan species globally distributed throughout tropical and warm temperate seas. In the northeastern tropical Pacific, this specie represents an important contribution to the biomass of artisanal and small-scale fisheries. Goals: In this study the aim was to obtain information about length frequency distribution and reproductive aspects of S. lewini, in Oaxaca, Mexico. Methods: Samples were taken from August 2001 to December 2007 in four landing sites of the artisanal fleet on the coast of Oaxaca. Results: Samples were collected 388 females and 434 males. Total length ranged from 44-308 cm for males and from 44-332 cm for females. The catches were made up of neonates (24.3%, 44-74 cm), juveniles (42.2%, 75-170 cm) and adults (33.5%, > 170 cm). The sex ratio shows differences by size, and season. The greatest catches were recorded in the rainy season (85.5%), with a predominance of juveniles and adults, and a higher proportion of males. In the dry season (15.5%) were recorded with a predominance of larger sizes >100 cm in both sexes. The females reached sexual maturity (TL50) at 198.8 cm and the males at 181 cm, based on characteristics and measurements of reproductive organs. A total of 37 gravid females with sizes between 175 and 281 cm were registered, from April to August. Gravid females had between 15-42 embryos, varying from 44-54 cm. Conclusion: S. lewini was present year round in the study area with the greatest catch from April to September, the season when pregnant females were present. Antecedentes: Sphyrna lewini, es una especie semi-oceánica y cosmopolita distribuida en aguas tropicales y templadas cálidas. En el océano Pacífico tropical noreste representa una contribución importante a la biomasa de la pesca artesanal y de pequeña escala. Objetivos: El objetivo de este estudio fue obtener información sobre la distribución de tallas y aspectos reproductivos de S. lewini en la costa de Oaxaca, México. Métodos: Entre agosto 2001 y diciembre 2007 se recolectaron muestras en cuatro sitios de desembarco de la flota artesanal de la costa de Oaxaca. Se colectaron 388 hembras y 434 machos. Resultados: La longitud total fue de 44-308 cm para machos y 44-332 cm en hembras. Las capturas estuvieron conformadas por neonatos (24.3%, 44-74 cm), juveniles (42.2%, 75-170 cm) y adultos (33.5%, >170 cm). La proporción sexual presentó diferencias por tallas y temporada. Las mayores capturas se registraron en lluvias (85.5%), con predominancia de juveniles y adultos y una mayor proporción de machos; en temporada de secas (15.5%) predominaron tallas >100 cm de ambos sexos. Las hembras alcanzan la talla de primera madurez (LT50) a los 199 cm y los machos a los 181 cm. Se registraron 37 hembras grávidas con tallas de 175 a 281 cm, entre los meses de abril a agosto. La fecundidad osciló de 15 a 42 embriones, con tallas entre 44 y 54 cm. Conclusiones: S. lewini estuvo presente casi todo el año, con las mayores capturas entre abril y septiembre, temporada en la cual las hembras preñadas estuvieron presentes

Ciclo reproductivo del molusco Atrina maura (Pterioidea: Pinnidae) en un sistema lagunar costero, al sur del Pacífico tropical mexicano

De febrero de 1997 a febrero de 1998, se recolectaron mensualmente muestras aleatorias del molusco Atrina maura en el sistema lagunar Corralero-Alotengo, Oaxaca, México. Se extrajeron las partes blandas para lavarlas in situ y fijarlas en solución Davison. En el laboratorio se pesaron para obtener los índices gonadosomático (IGS) y de rendimiento muscular (IRM), y mediante cortes histológico de las gónadas se caracterizó el ciclo reproductivo. Esta población se reproduce casi todo el año, con dos periodos reproductivos importantes: uno de abril a julio y otro de octubre a noviembre, y una sola época de reposo, en agosto y septiembre. El ciclo reproductivo tiene una relación directa con el IGS e inversa con el IRM. Hay evidencias de una relación estrecha de las época de desove y postdesove con la temperatura del agua (R = 0.991, p <IMG SRC="/img/revistas/rbt/v55n3-4/mayorigual.jpg" WIDTH=28 HEIGHT=24> 0.002). Las hembras predominaron casi todo el año, aunque esta proporción solo tuvo diferencias estadísticamente significativas en noviembre (X²: p= 0.05)<br>Reproductive cycle of the mollusk Atrina maura (Pterioidea: Pinnidae) in a coastal lagoon system of the Mexican South Pacific. From February 1997 to February 1998, random samples of the mollusk Atrina maura were collected on a monthly basis from the Corralero-Alotengo lagoon system, Oaxaca, Mexico. The soft parts were separated from the valve, washed in situ, and placed in a Davison solution. The gonadosomatic index (GSI) and the muscle yield index (MYI) were measured, and the reproductive cycle was characterized by histological cuts. A. maura has two important reproductive periods, one from April to July and another from October to November; there is a resting period from August to September. The reproductive cycle has a direct relationship with the GSI and a reverse relationship with the MYI. There was evidence of a close relationship of the spawning and post-spawning periods with the water temperature (R = 0.991, p = 0.002). Females dominate numerically throughout the year, but the difference is significant (X²: p= 0.05) only in November. Rev. Biol. Trop. 55 (3-4): 839-852. Epub 2007 December, 28

Abundancia, estructura poblacional y crecimiento de Atrina maura (Bivalvia: Pinnidae) en una laguna costera tropical del Pacífico mexicano

Mensualmente, de febrero a septiembre de 1997, mediante muestreo aleatorio simple con dos repeticiones, se estudió la abundancia, estructura poblacional y crecimiento del molusco bivalvo Atrina maura en diez estaciones distribuidas de manera uniforme, en un banco natural localizado dentro del sistema lagunar Corralero-Alotengo, Oaxaca, México. El análisis de la abundancia reveló diferencias estadísticas, altamente significativas entre las estaciones y entre los meses de muestreo (Kruskal-Wallis, p< 0.001). De acuerdo con el arreglo espacial de abundancia, se diferencian dos grandes grupos, uno de la boca a la región media del banco de A. maura y otro, de la mitad del banco hacia el interior del sistema lagunar. Temporalmente, se reconocieron tres períodos de abundancia; febrero-abril-mayo, julio-agosto, y marzo-junio-septiembre. La distribución de tallas, indica que A. maura se recluta al bentos de febrero a julio. Asimismo, aún cuando se encontró un amplio intervalo de tallas, dominan los organismos con longitud valvar mayor o igual a 15 cm (77.69%). Se estimó un crecimiento en talla de 3.7 cm/mes durante el periodo de secas (febrero a mayo) y de 3.5 cm/mes durante la temporada de lluvias (junio a septiembre). De febrero a mayo la proporción sexual fue 1:1, la dominancia de machos fue evidente en el período de junio a septiembre, y se detectó madurez gonadal a partir de 10 cm de longitud valvar.<br>The abundance, population structure, and growth of the Pen-shell Atrina maura in the Corralero-Alotengo tropical lagoon system in Oaxaca, Mexico, were studied from February to September of 1997. An abundance analysis showed significant temporal and spatial differences (Kruskal-Wallis, p< 0.001). Two spatial groups of abundance were found in the area, one from the mouth of the lagoon system to the middle of the Penshell bank, and the other between the middle of the Pen-shell bank and the head of the system. Three temporal periods of abundance were found (February-April-May; July-August; March-June-September). The distribution of population size showed that benthic recruitment of A. maura occurred from February to July. Length frequency of A. maura is commonly wide-ranging; nevertheless, in this study Pen-shell organisms with a valve length of 15 cm were frequently found. The growth rate length was 3.7 cm/month during the dry season (February to May), and 3.5 cm/month during the rainy season (June to September). Sex ratio was maintained at 1: 1 from February to May, but males were dominant from June to August, and the minimum length for reproduction was registered at 10 cm valve length

Coral connectivity between equatorial eastern Pacific marine protected areas: A biophysical modeling approach.

There are many marine protected areas (MPAs) containing coral reef aggregations in the eastern Pacific region. However, the connectivity of corals between MPAs is still poorly known, especially in the Marine Conservation Corridor of the Eastern Tropical Pacific (MCCETP). Here, we assess the potential connectivity of corals across equatorial eastern Pacific MPAs through a Lagrangian particle-tracking algorithm coupled offline with an ocean-circulation numerical model. Connectivity metrics and graph theory were used to analyze the networks and highlight those MPAs that are critical for maintaining the connectivity of corals across the region. Our results show that the equatorial eastern Pacific MPAs form a relatively well-connected network, at least 40% of coral larvae released per year end up within the boundaries of an MPA. MPAs like Malpelo and Gorgona islands included in the MCCETP were found to be critical for connectivity of corals because of their high betweenness centrality and potential role as stepping-stones between coastal MPAs and offshore MPAs such as the Galapagos Islands. Two pelagic larval duration (PLD) scenarios (40 and 130 days) indicate a quasi-unidirectional larval flow from coastal MPAs toward oceanic MPAs, where the only resilient MPAs (Coiba and Malpelo islands) depend mostly on subsidiary recruitment from MPAs located along the coast of Costa Rica, Panama and Colombia. In the two PLD scenarios, Cocos Island maintains a very low resilience potential. Our results indicate the imperative need to include coastal MPAs in the MCCETP network initiative, since connectivity and resilience of coral reefs in the equatorial eastern Pacific region rely heavily on coastal MPAs

The New Pelagic Operational Observatory of the Catalan Sea (OOCS) for the multisensor coordinated measurement of atmospheric and oceanographic conditions

The new pelagic Operational Observatory of the Catalan Sea (OOCS) for the coordinated multisensor measurement of atmospheric and oceanographic conditions has been recently installed (2009) in the Catalan Sea (41°39'N, 2°54'E; Western Mediterranean) and continuously operated (with minor maintenance gaps) until today. This multiparametric platform is moored at 192 m depth, 9.3 km off Blanes harbour (Girona, Spain). It is composed of a buoy holding atmospheric sensors and a set of oceanographic sensors measuring the water conditions over the upper 100 m depth. The station is located close to the head of the Blanes submarine canyon where an important multispecies pelagic and demersal fishery gives the station ecological and economic relevance. The OOCS provides important records on atmospheric and oceanographic conditions, the latter through the measurement of hydrological and biogeochemical parameters, at depths with a time resolution never attained before for this area of the Mediterranean. Twenty four moored sensors and probes operating in a coordinated fashion provide important data on Essential Ocean Variables (EOVs; UNESCO) such as temperature, salinity, pressure, dissolved oxygen, chlorophyll fluorescence, and turbidity. In comparison with other pelagic observatories presently operating in other world areas, OOCS also measures photosynthetic available radiation (PAR) from above the sea surface and at different depths in the upper 50 m. Data are recorded each 30 min and transmitted in real-time to a ground station via GPRS. This time series is published and automatically updated at the frequency of data collection on the official OOCS website (http://www.ceab.csic.es/~oceans). Under development are embedded automated routines for the in situ data treatment and assimilation into numerical models, in order to provide a reliable local marine processing forecast. In this work, our goal is to detail the OOCS multisensor architecture in relation to the coordinated capability for the remote, continuous and prolonged monitoring of atmospheric and oceanographic conditions, including data communication and storage. Accordingly, time series of measurements for a number of biological parameters will be presented for the summer months of 2011. Marine hindcast outputs from the numerical models implemented for simulating the conditions over the study area are shown. The strong changes of atmospheric conditions recorded in the last years over the area have altered the marine conditions of living organisms, but the dimension of the impact remains unclear. The OOCS multisensor coordinated monitoring has been specifically designed to address this issue, thus contributing to better understand the present environmental fluctuations and to provide a sound basis for a more accurate marine forecast system