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Abstract: Samples obtained in the entrance of the Sea of Cortés were used to study the distribution of euphausiids. This area has a complex hydrography with mixing of the California Current water from the north with Gulf of California and tropical waters arriving from the south probably from the warm pool in southern México, as shown by satellite images and hydrography. The origin of the different water masses is also reflected in their species composition. Three sectors can be recognized according to hydrographic evidence: North, South, and East, with each showing differences in species composition. The dominant species was the neritic low- oxygen-affinity species Euphausia lamelligera, followed by Euphausia eximia, Euphausia tenera, and Euphausia distinguenda. Significant differences exist in postlarval abundance between the three sectors. Early larval stages were found everywhere, but frontal areas of the southern open-ocean sector showed higher abundances, implying greater reproductive activity. E. lamelligera was dominant near the coast in the east sector, and E. eximia, E. distinguenda and E. tenera were dominant in the northern and southern open-ocean sectors. E. tenera was the most abundant species in the western open-ocean transect, but was found mixed with other non-neritic species. Higher diversity indices were found in the northern and southern (open-ocean) sectors; however, diversity indexes were higher at night. This mixing of species was presumably caused by horizontal mixing induced from a large eddy that covers both sectors as shown by the geostrophic currents derived from altimeter data. Complex summer species distributions reflect the complex hydrographic conditions of the area, with water masses mixing, and, consequently, mixing of species with different water mass affinities. [Copyright &y& Elsevier]

Abstract: The mechanisms governing dispersion processes in the northern Yucatan coast are investigated using a barotropic numerical model of coastal circulation, which includes wind-generated and large scale currents (i.e. Yucatan Current). This work provides the foundations for studying the dispersion of harmful algal blooms (HABs) in the area. Modelling experiments include effects of climatic wind (from long term monthly mean NCEP reanalysis), short term wind events (from in situ point measurements), and Yucatan Current (YC) characteristics. Its magnitude was approximated from published reports, and its trajectory from geostrophic current fields derived from altimeter data. These provided a range of real and climatic conditions to study the routes in which phytoplankton blooms may travel. The 2-D model results show that a synthetic and conservative bloom seeded in the Cabo Catoche (CC) region (where it usually grows), moves along the coast to the west up to San Felipe (SF), where it can either move offshore, or carry on travelling westwards. The transport to the west up to SF is greatly influenced by the trajectory, intensity and proximity of the YC jet to the peninsula, which enhances the westward circulation in the Yucatan Shelf. Numerical experiments show that patch dispersion is consistently to the west even under the influence of northerly winds. When the YC flows westward towards the Campeche Bank, momentum transfer caused by the YC jet dominates the dispersion processes over wind stress. On the other hand, when it flows closer to Cuba, the local processes (i.e. wind and bathymetry) become dominant. Coastal orientation and the Coriolis force may be responsible for driving the patch offshore at SF if external forcing decreases. [Copyright &y& Elsevier]

Abstract: Temperature and salinity anomalies derived from observations obtained in the period 1997–2008 are used to study the changes in physical properties off the Baja California west coast (24–31N). Near surface anomalies were used to characterize four periods of distinctive variability: (1) a warm and saline phase of El Niño 1997–1998, (2) a saline period from 1999 to 2002, (3) fresh subarctic water in 2002–2006, and (4) a saline-fresh (El Niño-La Niña) phase in late 2006 to early 2008. Subsurface (200m) salinity anomalies depicted a trend towards saltier conditions (ΔS∼0.1) from 2001 onwards, and did not show the four periods discernible near surface. EOF analysis of sea surface wind stress and wind stress curl suggested that after the intense westerly winds in late 2001, freshening during late 2002–2006 was due to the weakening (strengthening) of the North Pacific Current (Aleutian Low), and to a decrease of wind stress curl produced upwelling. Data also showed differences in the timing and magnitude of anomalies observed between the north (poleward of 28N) and the south (equatorward of 28N). Subsurface geostrophic currents demonstrated the existence of two large scale cyclonic gyres, one associated with a subarctic domain in the northern region, and another having tropical characteristics. The likely role of subsurface cyclonic pairs in the definition of a provincial boundary, and the importance in influencing the CCS ecosystem, are discussed. [Copyright &y& Elsevier]

The distribution and transport of paralarvae of the complex Sthenoteuthis oualaniensis - Dosidicus gigas (SD complex, Cephalopoda: Ommastrephidae) in the tropical-subtropical convergence off Mexico were analyzed under contrasting interannual environmental conditions. Two El Niño years were sampled (2010 and 2016), in which the SST were up to 3 °C above the average throughout the study area, while during La Niña year (2012) the SST anomalies were up to 2 °C below the average. During El Niño years, a relative shallow thermocline (<60 m depth) was detected around Cabo Corrientes, where the paralarvae were found with mean abundance of 2 org 1000 m−3. During La Niña condition, a shallower thermocline was detected in the entrance of the Gulf of California (~20 m depth) and the paralarvae abundance rose to 84 org 1000 m−3 with high frequency of occurrence. In both El Niño and La Niña conditions the paralarvae were mainly found in the strongly stratified waters (>80 cycles h−1). In addition, a simple dispersion Lagrangian model based on observed satellite geostrophic currents, suggested association of the SD complex paralarvae with mesoscale structures, in which the eggs and hatched paralarvae had an appropriate habitat for a nursery, retaining the paralarvae until their recruitment in a ~100 km radius. But during warm extreme events, with less mesoscale activity, the paralarvae could be transported as far as 500 km southeast of the spawning zone. Even though the interannual ENSO conditions modulate the magnitude of the paralarvae abundance, the shallow and well developed thermocline could help paralarvae to increase their survival chances, while mesoscale activity retains them near the productive coastal waters. • ENSO phases modulate Sthenoteuthis-Dosidicus complex paralarval abundance. • Mesoscale eddies retain paralarvae near coastal waters. • Lack of mesoscale eddy circulation leads to high paralarval dispersion rate. [ABSTRACT FROM AUTHOR]