Resumen del producto

Ocean fronts are dynamic structures that affect marine ecosystems. In the Gulf of California, the intense mixing by tide favors the formation of fronts in the archipelago of the Great Islands. The objective of this study is to identify thermal fronts and determine their effect on the spatial distribution of pelagic fish larvae. The CTD data and the zooplankton samples come from two oceanographic cruises carried out in summer (June 2006) and winter (February 2007) during live tides. The zooplankton samples were obtained by opening-closing networks (505 µm) at three depth levels (0-50 m, 50-100 m and 100-150 m). The surface temperature gradient of the sea during the cruise days was calculated from satellite images of AVHRR, using the contextual median filter method. The results show that the most intense thermal front (> 0.6) in the region was located south of Isla de la Guarda in both seasons, but with seasonal variability associated with the intense tidal mixing of the archipelago region and the circulation of the gulf. In summer, the front position was longitudinal to the main axis of the gulf, where the greatest abundance of fish larvae was concentrated. However, the position of the front could have allowed the dispersion of organisms towards the north influenced by the cyclonic circulation of summer. In winter, the position of the front was transversal to the main axis of the gulf, in which the greater abundance of fish larvae was also concentrated. The position of the front may have limited the larval dispersion between the south and north of the gulf. It is concluded that the influence of the thermal front located south of Isla de La Guarda affects the distribution of organisms with planktonic stages; and possibly contributes to the endemism of the northern region of the Gulf of California.

Palabras clave: Thermal front; Fish larvae; Gulf of California

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