Zooplankton assemblages in De ghi lagoon, Binh Dinh province

Abstract

This paper presents the results of zooplankton surveys in De Gi lagoon 2009, 2010, and 2020. Change of zooplankton communities was analyzed based on species richness, diversity, abundance, and species composition over the three sampling time points. In De Gi lagoon, the copepod group (subclass Hexanauplia) dominated with 61 in 85 zooplankton identified species, followed by Hydrozoa and Malacostraca with seven and five species, respectively. The remaining groups (Polychaeta, Branchiopoda, Ostracoda, Sagittoidea, Appendicularia, Thaliacea, Tentaculata, and Gastropoda) had low species richness, varied from 1 to 2 species. The Copepod assemblages compose mainly small species and have good adaptation in high salinity variabilities, such as Paracalanus and Acartia. In the lagoon, species richness and diversity increased from the upper lagoon to the lagoon's mouth over the years, but most pronounced in 2020. The average zooplankton density this year was low, 9.136 inds.m-3, much lower than in 2009 with 54.022 inds.m-3. Cluster analysis demonstrated the complexity of the zooplankton structure in the lagoon when the similarity in species composition between seasons and years is ca. 27%. Seasonal changes in zooplankton assemblages presented 58-73% dissimilarity, with the dry season having higher diversity, biomass, and calanoid copepodites and larvae. After ten years, since 2010, the zooplankton assemblages differed by 60-72% with higher diversity and lower abundance but remained similar ratios between dominant Calanoida and other orders in the copepod assemblages. Invertebrate larval abundance in De Gi lagoon should be considered as an important resource for their dominance and variation between seasons and distribution. This research provides basic scientific data on the zooplankton communities of De Gi lagoon, which has not been published before, contributing the baseline to any further studies the South-Central Viet Nam.