Cross-shelf and vertical structure of pelagic amphipods (Crustacea) related to hydro-meteorological conditions in the neritic zone, southern Gulf of Mexico

The environmental drivers that effect the pelagic amphipod communities in the neritic province have received little attention worldwide. This study analyzed the influence of fluvial discharges and wind regime on the pelagic amphipods in neritic waters of the southern Gulf of Mexico during two contrasting seasons: May (dry, lower discharges and wind speeds) and November (nortes, higher discharges and wind speeds). Zooplankton samples were collected at five depth levels of the water column (0–6, 6–12, 12–18, 45–55, and 95–105 m) using a stratified opening-closing net system. Environmental gradients were assessed by defining three horizontal assemblages (‘coastal’, ‘neritic’, ‘slope’) and two vertical assemblages (‘surface’: 0–18 m; ‘deep’: 45–105 m). Seasonally, the greater volume of nutrient-rich discharges during nortes resulted in a higher amphipod density. Spatially, low salinity waters off river mouths corresponded to the lowest amphipod density and diversity. The horizontal and vertical assemblages showed significant differences during the dry (ANOSIM test, p