Comparison of pteropod assemblages and their relationship with environmental variables in the southern Gulf of Mexico

A comparison of pteropod assemblages and their relationship with environmental factors in the southern coastal and oceanic zones of the Gulf of Mexico (GM) was performed during the springs (May-June) of 2006 and 2010. Zooplankton samples came from catches of 136 oblique tows with a Bongo net (0.61m in mouth diameter; mesh 505 mu m) and included 20 species of Euthecosomata, six of Pseudothecosomata, and three species and three genera of Gymnosomata. Four new records were found for the area (Diacavolinia strangulata, Cymbulia sibogae, Paraclione longicaudata and Thliptodon diaphanus). The most abundant species were Creseis conica, Limacina trochiformis and Creseis acicula, followed by Heliconoides inflatus. Pteropod abundance was higher in the neritic zone, particularly in the area of the epicontinental water discharge at the coastal front of the Veracruz-Tabasco zone, while higher diversity was observed in the oceanic zone. The cluster analyses and canonical correspondence analyses showed two assemblages (station groups) in each period: Oceanic and Coastal. The Oceanic assemblage was composed of species of oceanic origin with two indicator species (H. inflatus and Limacina lesueurii). This assemblage was correlated with increased sea surface temperature, at least during 2006, probably modulated by the influence of the Loop Current. The Coastal assemblage included both oceanic and neritic species and was subdivided into three, geographically distinct, station zones: (1) Veracruz-Tabasco zone characterized by Desmopterus papilio and L. trochiformis, their abundances inversely correlated with salinity and increased CO2, and influenced by river discharges and the narrow continental shelf; (2) Yucatan zone characterized by C. conica as an indicator species (2006); and (3) Confluence zone characterized by C. acicula (Laguna de Terminos). Yucatan and Confluence zones were characterized by elevated pH, and reduced turbidity and temperature, at least during 2010.