Zooplankton community changes across the Coringa mangrove and adjacent waters of east coast of India: insights into habitat-specific interactions with environmental changes.

Zooplankton in the mangrove and coastal waters play an important role in higher trophic levels. This study examines the zooplankton abundance and community changes across the Coringa mangrove creeks, Kakinada Bay, and the coastal waters of the Bay of Bengal. It focuses on their interactions with key environmental factors such as temperature, salinity, dissolved oxygen, nutrients, and chlorophyll-a. By analysing three distinct regions: (1) the mangrove ecosystem, including upstream and downstream creeks, (2) the adjacent bay, and (3) the connected coastal waters, providing insights into zooplankton variations in response to environmental changes across interconnected habitats. The results indicate significant variation in environmental variables, with salinity showing a prominent decreasing gradient (p < 0.0001; n = 29), markedly toward the upstream mangrove regions. A total of 67 zooplankton taxa were recorded, with copepods emerging as the dominant group and exhibiting marked spatial variation across the study area. Holoplanktonic organisms such as the freshwater cladoceran Daphnia sp. and euryhaline copepods Acartia clausi and Oithona brevicornis, along with meroplanktonic forms including fish eggs, fish larvae, and molluscan larvae, were particularly prominent in the mangrove creek habitats. Salinity influences zooplankton variation, highlighting its role in shaping the community structure. The diversity index and the meroplankton to holoplankton ratio revealed distinct variation between the coastal and mangrove-influenced environments. Cluster analysis identified distinct assemblages of zooplankton taxa, reflecting habitat-specific environmental conditions. The RDA analysis underscores the relationships between environmental factors and dominant zooplankton taxa, providing valuable insights for zooplankton assemblages in different habitat conditions.