Composition and abundance of macro zooplankton in the coastal waters off the El Mogote Sandbar

Background. Bahía de la Paz, Mexico have seasonal blooms of planktonic prey that support a range of marine species including whale sharks (Rhincodon typus). Goals. This study includes the first sampling cycle that covers all climatic seasons, to know changes in the abundance and composition of zooplankton in the coastal waters off the El Mogote Sandbar, in Bahía de La Paz, BCS, Mexico. Methods. A total of 96 plankton samples were collected at predetermined field stations, spanning the entire length of the El Mogote from June 2016 to May 2017. Results. Total biomass was significantly different between seasons (Kruskal-Wallis chi-squared = 29.993, p = 0.000001385), with the lowest biomass recorded in spring (176.28 ml 100 m^-3, 10.1%); and highest observed for winter (703.04 ml 100 m^-3, 40.4%). Zooplankton composition was largely comprised of two main taxonomic groups: Copepoda (396,234 organisms100 m^-3, 43.1%) and Chaetognatha (196,986 organisms100 m^-3, 21.4%). The total number of individuals (sum of all taxonomic groups) per season showed significant differences (Kruskal-Wallis chi-squared = 29.78, p = 0.000001533) with the highest concentrations recorded in winter (292,429 organisms100 m^-3, 31.8%) and lowest in spring (162,995 organisms100 m^-3; 17.7%). Conclusions. This information provides the first work focused solely in the El Mogote area as a main foraging site for whale sharks, with clear changes in plankton communities with respect to shifting climatic seasons, and the importance of certain taxonomic groups to the diet of whale sharks.