Phytoplankton Assemblage in the Campeche Canyon (Southern Gulf of Mexico) and Its Relationship with Hydrography During a “Nortes” Storm Season

The Gulf of Mexico is a marginal sea recognized as one of the world’s Large Marine Ecosystems. It is characterized by significant climate variability that influences phytoplankton communities. In this paper we investigated the phytoplankton assemblages in the Campeche Canyon, located in the Southern Gulf of Mexico, during a “Nortes” storm season. Additionally, we assessed the role of hydrographic conditions and circulation patterns in species distribution. The assessment was based on in situ observations collected during a multidisciplinary research cruise conducted in February 2011. High-resolution hydrographic data were gathered using a CTD sonde, and water samples were collected at various depths for phytoplankton cell analysis. The findings revealed a deep thermocline at a depth of 90 m, with a deep chlorophyll-a maximum (DCM) occurring below 75 m. The circulation pattern in the area was dominated by a dipole eddy, consisting of both cyclonic and anticyclonic movements, which created strong currents at the edges. The species composition varied by depth; a total of 77 species were identified in the surface waters, while the DCM exhibited a richness of 81 species. In the surface waters, dinoflagellates were the most abundant group, comprising 41 species, whereas diatoms were more prevalent in the DCM, with 44 species identified. In terms of abundance, dinoflagellates were more prevalent at both depths, with concentrations reaching up to 12,000 cells L−1. The most abundant species identified included the ciliate Mesodinium rubrum, the cyanobacteria Trichodesmium hildebrandtii, the diatoms Asteromphalus cleveanus and Pseudo-nitzschia multistriata, the dinoflagellates Lingulaulax polyedra and Blepharocysta denticulata, and the silicoflagellate Dictyocha fibula. Analysis of the horizontal distribution patterns of phytoplankton species revealed that species tend to aggregate in areas with strong currents. These findings enhance our understanding of phytoplankton dynamics in the Campeche Canyon, particularly during climatic seasons when in situ observations are limited due to challenging navigation conditions caused by “Nortes” storms.