Liu, H.; Zhang, X.; Yang, Q.; Zuo, T., and Quigg, A., 2017. Mesozooplankton dynamics in relation to environmental factors and juvenile fish in a subtropical estuary of the Gulf of Mexico.Estuaries are physically dynamic and biologically productive but are also vulnerable to human activities and natural stressors. Zooplankton are sensitive to environmental changes and play a pivotal role in the transfer of the energy from primary producers to fish in marine ecosystems. Focusing on a subtropical estuary of Galveston Bay (Texas) in the northern Gulf of Mexico, the seasonal variations of species composition, abundance, and diversity of mesozooplankton in relation to environmental factors were examined, and the trophic interactions between zooplankton and juvenile fish were explored for the period of 2008 and 2009. The results showed that copepod nauplii, Acartia tonsa, Paracalanus spp., and Oithona spp. were the numerically dominant taxa in the bay. Zooplankton abundance was significantly and positively correlated to seawater temperature, whereas zooplankton diversity was positively related to salinity. When focusing on copepods only, their abundance was significantly and positively related to temperature, and the abundance and species diversity of copepods were positively and significantly related to salinity, implying that tidal advection of coastal ocean water likely carries diverse copepod species into the estuary. The relative abundance of the young of year (YOY) forage fish of Bay anchovy (Anchoa mitchilli) and Gulf menhaden (Brevoortia patronus) exhibited synchronous (no lag) significant associations with the abundance of zooplankton and the abundance and diversity of copepods. YOY of Atlantic croaker (Micropogonias undulatus), with a lag of 3 months, was significantly correlated with the abundance of zooplankton. Given the limited relevant research in the Gulf estuaries, the role of mesozooplankton in relation to environmental factors and the implications for juvenile fish in subtrophical estuaries need to be more fully assessed.