Response of the abundance and size of Acartia (Acartiura) hongi (Copepoda: Calanoida) copepodites to environmental variables in Laizhou Bay, Bohai Sea

Acartia hongi is an endemic brackish and coastal copepod species in the Yellow and Bohai Seas. To investigate the population structure and distribution, we examined samples of A. hongi copepodites from May 2011 to April 2012, excluding the ice season. A generalized additive model (GAM) was used to explore the response of the abundance and prosome length (PL) of A. hongi to a range of environmental variables, including temperature, salinity, chlorophyll a (Chl a) content, Yellow River runoff, pelagic fish, and phytoplankton. A. hongi occurred throughout the survey season continuously and area widely in Laizhou Bay. It was a dominant species in the copepod community and showed a maximum abundance during April and May. The CI-CIII copepodites were the primary contributors to the total population of A. hongi during the blooming months. Population densities (>10,000 ind.m(-3)) occurred in nearshore waters with temperatures between 10 degrees C and 15degree celsius and salinities between 25 and 27. Mean PLs across all copepodite stages were shortest in August or September and longest in March. The best-fitting GAMs for copepodite abundance and PL included the variables of temperature, salinity, Chl a content, and runoff. The abundance of A. hongi copepodites decreased with increasing temperature, particularly for CI and CII copepodites, when the temperature exceeded 10-15degree celsius. Salinity and runoff showed more negative correlations with A. hongi copepodites of younger stages. The PLs across the copepodite stages demonstrated significant inverse correlations with temperature. Furthermore, the Chl a content significantly influenced the PLs of CVs and adults through interactions with temperature. Overall, this study highlights temperature as a critical factor for the abundance and size distribution of the A. hongi population. Copepodites at earlier stages are more sensitive to temperature and salinity fluctuations. These findings provide valuable insights into the environmental effects on the A. hongi population dynamics in Laizhou Bay.