Relationship Between Zooplankton Distribution and Hydrography in Deep Waters of the Southern Gulf of México. A Seasonal Study.

Samples obtained during three different seasons (XIXIMI 1, November 2010; XIXIMI 2, July 2011; and XIXIMI 3 February-March, 2013) were utilized to study zooplankton distribution and hydrography. We observe the same distributional pattern for the three seasons. In the south, in the Gulf of Campeche, where a quasi-permanent gyre was present, we found the most productive area, with high zooplankton bio volumes. During autumn and winter, coastal currents in the same area induced by wind forcing is apparently producing an upwelling, which, by Ekman pumping, is transporting, nutrients to the open ocean, increasing primary productivity. The depth of the isopycnes, showed, during the three cruises, a domed structure in the Gulf of Campeche (South of the area in front of Campeche and Veracruz states), around cyclonic and anticyclonic eddies; this in coincidence with high CDT fluorescence values and high bio volumes of zooplankton. The main zooplankton groups showed small seasonal variability, in their proportions, but a great seasonal variability in their abundances and bio volumes. For the three seasons sampled, a significant difference was found for the bio volumes. During summer 2011, after a strong rain event, great concentrations of salps were found in the Gulf of Campeche, and within the before mentioned eddies. Bio volumes during summer were 9 times higher than during autumn. Even excluding the salps volumes, during summer we did find significant differences among the bio volumes of the three cruises, with mean values (six for autumn, and two times higher for winter), than the other two seasons sampled. These results demonstrate that the Gulf of Campeche is a permanently higher productivity area, but with considerable seasonal differences.